Horned Grebe (Podiceps auritus): COSEWIC assessment and status report 2023

Official title: COSEWIC assessment and status report on the Horned Grebe (Podiceps auritus) in Canada

Special Concern

2023

COSEWIC assessment summary

Assessment Summary - December 2023

Common name

Horned Grebe

Scientific name

Podiceps auritus

Status

Special Concern

Reason for designation

Approximately 92% of the North American breeding range of this waterbird occurs in Canada, primarily in prairie and boreal wetlands of western and central Canada. A very small, disjunct group breeds on Quebec’s Magdalen Islands. Although Magdalen Islands birds were previously assessed separately, the species is now assessed as one population because the lack of evidence for unique adaptations no longer justifies separate assessment. Available data on population trends are mixed. However, the species is threatened by loss and degradation of wetland habitat, drought, collisions with power lines and other structures, and the potential for oil spills and fisheries bycatch on the wintering grounds. The overall impact of current and future threats may lead to declines of up to 30 percent over the species’ next three generations.

Occurrence

British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, Yukon, Northwest Territories, Nunavut, Pacific Ocean, Atlantic Ocean

Status history

In December 2023, the Magdalen Islands population and the Western population were considered as a single unit across the Canadian range, which was designated Special Concern.

COSEWIC executive summary

Horned Grebe

Podiceps auritus

Wildlife species description and significance

The Horned Grebe (Podiceps auritus) is a small waterbird with a long neck and short bill. It is named after the patch of erectable, buff-coloured feathers on its head, which extend from its eyes to the back of its nape. In breeding plumage, the Horned Grebe has a black face and back, with a chestnut foreneck and flanks. Two subspecies are recognized globally: P. a. auritus, which breeds in Eurasia, and P. a. cornutus, which breeds in North America.

Aboriginal (Indigenous) Knowledge

All species are significant and are interconnected and interrelated. There is no species-specific ATK in the report.

Distribution

The Horned Grebe is found in North America, Europe and Asia. Approximately 92% of the North American breeding range is in Canada, extending from Yukon and British Columbia to Quebec. However, most birds breed in the Prairies and the Northwest Territories. The North American population winters primarily in the United States, with the highest numbers along the Pacific and Atlantic coasts.

Habitat

The Horned Grebe breeds primarily in the Prairie and Boreal ecological areas, where it occupies small to moderately sized freshwater wetlands, and occasionally brackish or alkaline water bodies. Suitable breeding ponds have a mixture of emergent vegetation for nesting and open water for foraging. Pairs may occasionally occupy constructed wetlands, including borrow-pit ponds. The species primarily winters at inshore saltwater sites, but also uses medium to large freshwater lakes and ponds.

Biology

The generation length for Horned Grebe is estimated to be 4.4 years, with sexual maturity reached at one year. Nesting begins upon arrival on the breeding grounds, with egg-laying typically occurring between mid-May and mid-June; clutches contain between five and seven eggs on average. Incubation lasts 22 to 25 days, and the hatched young are fed by the parents for 14 days, and reach independence after 19 to 21 days. The species’ diet consists primarily of aquatic invertebrates in summer, and fish and crustaceans in winter.

Population sizes and trends

The Canadian population of the Horned Grebe is estimated to comprise 200,000 to 500,000 mature individuals. The Breeding Bird Survey (BBS) primarily samples the southern portion of the species’ Canadian breeding range and may not accurately reflect overall population trends. It indicates a long-term (1970 to 2019) Canadian trend of -1.71% per year (95% credible Interval [CI] = - 4.56, 0.67), amounting to an estimated -57.0% over 49 years (95% CI = - 89.9, 38.7). During the most recent three-generation period (2006 to 2019), the average trend was -1.11% per year (95% CI = -6.05, 4.54), or -13.5% for the entire period (95% CI = -55.5, 78.0). Christmas Bird Count (CBC) results at the continental scale likely better reflect the overall Canadian population, given that most birds winter in the United States. The long-term trend of 0.38% per year since 1970 (95% CI = -0.54, 1.59) amounts to an estimated increase of 21.3% over 51 years (95% CI = -24.1%, 123.6%). Over the most recent three-generation period (2008 to 2021), the average annual trend was estimated at 1.23% (95% CI = -3.22, 5.88), equivalent to 17.2% for the entire period (95% CI = -34.7, 110.2). However, these BBS and CBC trends are non-significant. In contrast, recently released trends derived from eBird data show significant three-generation (2007 to 2020) declines per count cell, primarily at median rates of decline greater than 30%, across the continental wintering range of the species, although a range-wide estimate is not yet available.

Threats

Permanent losses of wetlands resulting from activities associated with agriculture and aquaculture and energy production and mining threaten the Horned Grebe. Up to 70% of wetlands in the Prairie region have disappeared since European settlement, with some losses ongoing. Ecosystem modification due to invasive aquatic plants that reduce areas of open water and the eutrophication and degradation of nesting ponds due to agricultural activities also pose a threat to the Horned Grebe. Climate change is also affecting this species: the temporary drying of wetlands from precipitation changes can displace individuals or render habitat unsuitable. The Horned Grebe is also at risk of mortality from collisions with utility and service lines (power lines) and renewable energy infrastructure (wind turbines). On the wintering grounds, pollution from oil spills and bycatch of the species in fisheries can also negatively impact the population. The overall threat impact for the Horned Grebe over the next three generations (13 years) is estimated to be Medium.

Protection, status and recovery activities

In Canada, the Horned Grebe and its nest and eggs are afforded protection under the Migratory Birds Convention Act, 1994. The previous status report recognized two designatable units (Dus) for the Western and Magdalen Island populations, respectively. According to COSEWIC’s current DU guidelines, however, there is only one DU for this species in Canada. As of December 2023, COSEWIC combined the Magdalen Islands and Western populations in a single DU spanning the species’ entire Canadian range, and designated it as Special Concern.

However, the Western population is still listed as Special Concern, and the Magdalen Islands population, as Endangered, under the Species at Risk Act. In Quebec, this species is designated Threatened under the province’s Act Respecting Threatened or Vulnerable Species, and is protected under the Act Respecting the Conservation and Development of Wildlife. The species is also protected under the Migratory Bird Treaty Act in the United States. The International Union for the Conservation of Nature (IUCN) considers the Horned Grebe Globally Secure (G5) but Vulnerable. In Canada, it is ranked Secure (N5B, N4N5N). At the provincial and territorial levels, the Horned Grebe is considered S1B, S3N, S4M (Critically Imperiled as a breeding population) in Ontario, and S3 (Vulnerable) in Alberta, Manitoba and the Northwest Territories, with the other subnational ranks more secure. NatureServe still considers the species to have two subpopulations, ranking the Western subpopulation S3M and the Magdalen Islands population, S1B (Critically Imperiled).

Technical summary

Podiceps auritus

Horned Grebe

Grèbe esclavon

Range of occurrence in Canada: British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, Yukon, Northwest Territories, Nunavut, Pacific Ocean, Atlantic Ocean

Demographic information

Generation time (usually average age of parents in the population)

4.4 years

Bird et al. (2020).

Is there an [observed, inferred, or projected] continuing decline in number of mature individuals?

Unknown

Christmas Bird Count (CBC) data, which cover the wintering range of the Canadian population, indicate that the number of mature individuals is likely stable or increasing (non-significant trends). However, eBird trends maps provide similar coverage and show significant range-wide declines on the wintering grounds. Breeding Bird Survey (BBS) data (which have Low reliability for this species) show a non-significant decline.

[Observed, estimated, or projected] percent of continuing decline in total number of mature individuals within 3 years [or 1 generation; whichever is longer up to a maximum of 100 years]

Unknown

Unknown

Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations, whichever is longer up to a maximum of 100 years]

Unknown

CBC data suggest that the number of mature individuals has likely been stable or increasing over the last two generations. However, eBird trends maps show significant three-generation declines on the wintering grounds. BBS data (the reliability of which is low for this species) show a non-significant decline during this period.

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 years, or 3 generations, whichever is longer up to a maximum of 100 years].

Trend estimates from three survey methods vary from non-significant increase to significant decrease over past 3 generations

Estimated increase of 17.2% (95% CI -34.7, 110.2) over three generations (CBC); estimated decrease of

13.5% (-55.5, 78.0) over three generations (BBS).

Mapped eBird winter trends (28 December to 8 February; three generations) show significant declines per count cell, primarily at median rates of decline greater than 30%.

[Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations, whichever is longer up to a maximum of 100 years].

Unknown

BBS and eBird trends suggest non-significant and significant declines, respectively, while recent CBC trends indicate a non-significant increase. The projection is unknown because of (a) opposing trends; and (b) potential for threats (currently assessed as a Medium impact overall) to increase, for example, more severe drought due to climate change.

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over any period of [10 years, or 3 generations, whichever is longer up to a maximum of 100 years], including both the past and the future.

Unknown

Continental monitoring programs provide conflicting indications of trends, and climate-related and other threats may increase in future.

Are the causes of the decline clearly reversible?

No

Are the causes of the decline clearly understood?

No

Wetland loss is likely to be partially responsible for regional declines, particularly in the southern portion of the breeding range.

Have the causes of the decline ceased?

No

Loss of prairie wetlands to agricultural and commercial development is ongoing.

Are there extreme fluctuations in number of mature individuals?

No

Extent and Occupancy information

Estimated extent of occurrence (EOO)

5,003,843 km²

Calculated based on a minimum convex polygon around known occurrences during the breeding season

Index of area of occupancy (IAO), reported as 2x2 km grid value.

>2,000 km²

Details of distribution are insufficiently known to calculate IAO based on a 2 km x 2 km grid, but it is certainly much more than the threshold value of 2,000 km², given the species’ extensive range and large population.

Is the population “severely fragmented” that is, is >50% of its total area of occupancy in habitat patches that are (a) smaller than would be required to support a viable population, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse?

1. No
2. No

This species has a large, relatively contiguous population and geographical range, although the Magdalen Islands subpopulation is separated by > 2,000 km from the closest regular breeding sites.

Number of “locations” (use plausible range to reflect uncertainty if appropriate)

Unknown, but certainly much greater than 10

The greatest threat is agricultural land use, which is under the control of hundreds or thousands of managers.

Is there an [observed, inferred, or projected] continuing decline in extent of occurrence?

No

Geographical range is relatively unchanged for the Western subpopulation (3.9 million km² in this status report vs. 5.1 million km² in the previous report). EOO has now increased due to the addition of the Magdalen Islands subpopulation to the western one.

Is there an [observed, inferred, or projected] continuing decline in index of area of occupancy?

Unknown

Insufficient data available at a scale large enough to assess change in IAO.

Is there an [observed, inferred, or projected] continuing decline in number of subpopulations?

N/A

There were no subpopulations in the previous status report but, instead, two Dus (populations).

Is there an [observed, inferred, or projected] continuing decline in number of “locations”?

Unknown, but unlikely

Is there an [observed, inferred, or projected] continuing decline in [area, extent and/or quality of] habitat?

Unknown

The extent and quality of the habitat are projected to decline in some areas, but the overall change is difficult to predict. Shipping traffic is increasing in many portions of the wintering range (along with the related oil spill risk).

Are there extreme fluctuations in number of subpopulations?

No

See above.

Are there extreme fluctuations in number of “locations”?

Unknown, but unlikely

Are there extreme fluctuations in extent of occurrence?

No

Are there extreme fluctuations in index of area of occupancy?

No

Number of Mature individuals (in each subpopulation)

Western sub-population

200,000 to 500,000

Based on BirdLife International (2020) and Wetlands International (2020)

Magdalen Islands subpopulation

Likely < 10

Based on annual censuses (Canadian Wildlife Service, unpubl. data)

Quantitative analysis

Is the probability of extinction in the wild at least [20% within 20 years or 5 generations whichever is longer up to a maximum of 100 years, or 10% within 100 years]?

Unknown

Analysis not conducted

Threats and Limiting factors

Was a threats calculator completed for this species?

Yes (ECCC 2022; see Appendix 1)

Overall assigned threat impact: Medium (2020)

Key threats were identified as:

1. agriculture and aquaculture (IUCN 2) – low threat impact
2. energy production and mining (IUCN 3) – low threat impact
3. transportation and service corridors (IUCN 4) – low threat impact
4. biological resource use (IUCN 5) – low threat impact
5. natural system modifications (IUCN 7) – low threat impact
6. pollution (IUCN 9) – low threat impact
7. climate change (IUCN 11) – low threat impact

What limiting factors are relevant?

Prey abundance and high susceptibility to predation during the nesting period may be limiting.

Rescue effect (natural immigration from outside Canada)

Status of outside population(s) most likely to provide immigrants to Canada.

Secure

Considered secure (N5B) in the United States, although that population is very small compared to the one in Canada

Is immigration known or possible?

Yes

Unknown, but possible

Would immigrants be adapted to survive in Canada?

Yes

Habitat and climate similar to Canada

Is there sufficient habitat for immigrants in Canada?

Yes

Are conditions deteriorating in Canada?

Yes

Continuing land conversion is likely reducing habitat within the Prairie Region.

Are conditions for the source (that is, outside) population deteriorating?

Yes

Continuing land conversion likely reducing habitat in the U.S. source population

Is the Canadian population considered to be a sink?

No

Canada accounts for about 92% of breeding range.

Is rescue from outside populations likely, such that it could lead to a change in status?

No

Canada accounts for about 92% of breeding range.

Occurrence data sensitivity

Are occurrence data of this species sensitive?

No

Species is widespread and relatively abundant.

Status history

COSEWIC

In December 2023, the Magdalen Islands population and the Western population were combined in a single unit across the Canadian range, which was designated Special Concern.

Status and reasons for designation

Status:

Special Concern

Alpha-numeric codes

Not applicable

Reason for change of status

Not applicable – no change in status (former Western population)

Former Magdalen Islands population (Endangered) now considered part of a single, Canada-wide DU, based on updated DU criteria (COSEWIC 2020) – change code IVii

Reasons for designation (2023)

Approximately 92% of the North American breeding range of this waterbird occurs in Canada, primarily in prairie and boreal wetlands of western and central Canada. A very small, disjunct group breeds on Quebec’s Magdalen Islands. Although Magdalen Islands birds were previously assessed separately, the species is now assessed as one population because the lack of evidence for unique adaptations no longer justifies separate assessment. Available data on population trends are mixed. However, the species is threatened by loss and degradation of wetland habitat, drought, collisions with power lines and other structures, and the potential for oil spills and fisheries bycatch on the wintering grounds. The overall impact of current and future threats may lead to declines of up to 30 percent over the species’ next three generations.

Applicability of criteria

A: Decline in total number of mature individuals

Not applicable. Different population monitoring sources are contradictory, showing a decreasing, stable or increasing population, albeit with wide confidence intervals surrounding most point estimates.

B: Small distribution range and decline or fluctuation

Not applicable. EOO and IAO far exceed thresholds for Threatened.

C: Small and declining number of mature individuals

Not applicable. Number of mature individuals is at least 200,000, exceeding the threshold for Threatened.

D: Very small or restricted population

Not applicable. Number of mature individuals is at least 200,000, exceeding the threshold for Threatened D1, and not severely restricted and vulnerable to stochastic effects as required for D2.

E: Quantitative analysis

Not applicable. Analysis not conducted.

Special Concern (b; calculated threat level of Medium suggests that species may become threatened; and c; eBird cell-level trends suggest that species is close to qualifying for Threatened status under the A criterion)

Preface

The Horned Grebe was first assessed by COSEWIC in April 2009, and designated Special Concern (Western population) and Endangered (Magdalen Islands population). Since then, COSEWIC’s criteria for recognizing designatable units (Dus) have been refined (COSEWIC 2020), such that the group of birds breeding on the Magdalen Islands no longer qualifies as a separate DU. These birds now form a single DU with all Canadian conspecifics, with the western and Magdalen Islands groups considered here as two subpopulations within one DU rather than two separate populations.

Knowledge of the species’ breeding distribution has improved with the completion of the second Quebec breeding bird atlas, the publication of the first breeding bird atlases for Manitoba and British Columbia, and data collection for the first Saskatchewan breeding bird atlas. Analytical approaches used to estimate trends from the data obtained in the North American Breeding Bird Survey and Christmas Bird Count have improved (for example, Soykan et al. 2016; Meehan et al. 2020), with results available through to 2021, and trends estimates using data held in eBird are also now available (Fink et al. 2022). Recent research also includes a review of population trends in Manitoba (Hammell 2017).

Both a federal recovery strategy and an action plan have been produced for the (former) Magdalen Islands population (Environment Canada 2013, 2015), and a management plan has been formulated for the (former) Western population (ECCC 2022)

COSEWIC history

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2019)

Wildlife species

A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)

A wildlife species that no longer exists.

Extirpated (XT)

A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A wildlife species facing imminent extirpation or extinction.

Threatened (T)

A wildlife species likely to become endangered if limiting factors are not reversed.

Special concern (SC)
(Note: Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.)

A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at risk (NAR)
(Note: Formerly described as “Not In Any Category”, or “No Designation Required.”)

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data deficient (DD)
(Note: Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” [insufficient scientific information on which to base a designation] prior to 1994. Definition of the [DD] category revised in 2006.)

A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.

The Canadian Wildlife Service, Environment and Climate Change Canada, provides full administrative and financial support to the COSEWIC Secretariat.

Wildlife species description and significance

Name and classification

Current classification:

Class: Aves

Order: Podicipediformes

Family: Podicipedidae

Genus: Podiceps

Species: auritus

Subspecies in Canada:

Two subspecies of the Horned Grebe are recognized: P. a. auritus (Slavonian Grebe) which breeds in northern Eurasia, and P. a. cornutus (Horned Grebe), which breeds in North America (del Hoyo et al. 1992). Only P. a. cornutus has been documented in Canada.

Common names:

English: Horned Grebe, Slavonian Grebe, Hell-diver

French: Grèbe esclavon, Grèbe cornu

Synonyms and notes:

The Horned Grebe is a member of the family Podicipedidae, which contains 22 species in six genera. The genus Podiceps comprises eight extant species, including three that breed in Canada: Red-necked Grebe (Podiceps grisegena), Eared Grebe (P. nigricollis), and Horned Grebe (P. auritus) (Winkler et al. 2020).

Description of wildlife species

The Horned Grebe is a small diving waterbird (length: 31 to 38 cm; weight: 300 to 570 g; see cover photo), with a relatively long neck and a short, pointed bill (Stedman 2020). In alternate (breeding) plumage, the Horned Grebe has a patch of erectable, bright buff feathers (“horns”) that extend from its vibrant red eyes to the back of its nape. The crown, cheeks and back are black and the belly is white, while the foreneck, lores, flanks and upper breast are chestnut. Males and females are similar in appearance, with females slightly smaller and lighter in size and duller in coloration (Sibley 2014; Stedman 2020). The basic (winter) plumage of Horned Grebe is much more subdued, consisting of mostly grey and white (Sibley 2014; Stedman 2020). Juveniles are very similar to adults in basic plumage (Stedman 2020).

Designatable units

Using three types of genetic markers—mitochondrial DNA (mtDNA) sequence, nuclear intron sequence, and 25 amplified fragment length polymorphism loci (AFLPs)— Boulet et al. (2005) found moderate but significant differences between the two Horned Grebe subspecies (that is, North America versus Iceland), but only subtle structural differences between the two subpopulations of P. a. cornutus in North America (western Canada and the Magdalen Islands in Quebec; Figure 1). Although Boulet et al. (2005) detected significant allele frequency differences in the mitochondrial DNA sequence and AFLP markers of the two subpopulations, the subpopulations were not phylogeographically distinct (that is, there was no evidence of reciprocal monophyly among regional groups), and there was some evidence of gene flow (even if limited) between subpopulations. Based on the significant allele frequency differences in mtDNA and AFLP markers, Boulet et al. (2005) suggested that these two subpopulations constitute different management units (MUs). MUs are demographically independent populations identified to assist in the short-term management of larger entities (Moritz 1994). MUs are different from designatable units (Dus) or evolutionarily significant units, which are defined based on historical population structures, mtDNA phylogeny and long-term conservation needs (Moritz 1994).

COSEWIC (2020) recognizes Dus (units below the level of taxonomic species) on the basis of attributes indicating both discreteness and evolutionary significance. Populations are considered to be discrete if there is very little transmission of heritable information from other populations, and to be evolutionarily significant if they have distinct adaptive traits or an evolutionary history not found elsewhere in Canada.

Discreteness can be recognized on the basis of heritable traits or markers (“for example, evidence from genetic markers or heritable morphology, behaviour, life history, phenology, migration routes, vocal dialects”) that clearly distinguish the DU (D1 criterion), or on the basis of “natural disjunction…such that transmission of information…has been severely limited for an extended time” (D2) (COSEWIC 2020).

Figure 1. Breeding and wintering range of the Horned Grebe (Podiceps auritus) in North America. Adapted from COSEWIC (2009), Fink et al. (2020) and Stedman (2020).

With regard to the D1 criterion, no morphological or biological differences between the Western and Magdalen Islands subpopulations are known, and the only documented behavioural difference involves migration routes. It is not known where the Magdalen Islands subpopulation overwinters, but its wintering areas are presumably along the U.S. Atlantic coast and may overlap to some degree with those used by individuals from western North America that also overwinter along that coast. Overall, considering that Boulet et al. (2005) concluded that the Magdalen Islands subpopulation was not phylogeographically distinct, there is some evidence in support of D1. For criterion D2, there is a natural disjunction of more than 2,000 km between the two subpopulations’ closest regular breeding sites (that is, northwestern Ontario and Île du Cap aux Meules in the Magdalen Islands; Cadman et al. 2007; Robert et al. 2019). However, genetic information supports the conclusion that the subpopulation is not “naturally disjunct” (D2), as the F_st values for the AFLP data are low (0.04), indicating considerable gene flow, and the minimum spanning-network for mitochondrial ND2 data is star-shaped, indicating a lack of genetic population structure (Boulet et al. 2005; Taylor pers. comm. 2022).

If either discreteness criterion is met, evolutionary significance can be considered. Evolutionary significance is based on evidence or strong inference that the Dus have been on independent evolutionary trajectories over a significant period, often reflecting origins in separate Pleistocene refugia (S1; COSEWIC 2020), or evidence or strong inference that they possess adaptive, heritable traits that cannot be practically reconstituted if lost (S2). Although it is unknown how long the Horned Grebe has been established on the Magdalen Islands—in 1887, “Colymbus auritus” was recorded as an uncommon breeder in one of the earliest known surveys of the islands (Bishop 1889)—the moderate but not phylogeographically significant levels of divergence in mtDNA (Boulet et al. 2005) indicate that S1 does not apply. The lack of genetic structure found by Boulet et al. (2005; that is, the minimum spanning-network they found [their Fig. 1] exhibited a typical star-like shape, without clear regional subgroups), the limited power of population assignment, and the “non-exclusion of all Quebec birds from British Columbia and the west central populations” (Boulet et al. 2005;. 547) suggest that there is possibly immigration from the Western subpopulation (or relatively recent colonization), and so negates the applicability of S2.

On the basis of these lines of evidence, Boulet et al. (2005) suggested that the Magdalen Islands subpopulation could be considered a distinct management unit. Although this subpopulation may meet COSEWIC’s definition of discreteness due to its different migratory route, the available evidence indicates that it falls short of COSEWIC’s thresholds for evolutionary significance. The Horned Grebe is therefore treated in this report as a single DU within Canada.

Special significance

Canada has special responsibility for Horned Grebe, since approximately 92% of the breeding range of the North American subspecies (P. a. cornutus) occurs in the country (COSEWIC 2009).

Aboriginal (Indigenous) knowledge

Aboriginal Traditional Knowledge (ATK) is relationship-based. It involves information on ecological relationships between humans and their environment, including characteristics of species, habitats and locations. Laws and protocols for human relationships with the environment are passed on through teachings and stories, and Indigenous languages, and can be based on long-term observations. Place names provide information about harvesting areas, ecological processes, spiritual significance or the products of harvest. ATK can identify life history characteristics of a species or distinct differences between similar species.

Cultural significance to Indigenous peoples

There is no species-specific ATK in the report. However, Horned Grebe is important to Indigenous Peoples who recognize the interrelationships of all species within the ecosystem.

Distribution

Global range

The Horned Grebe is widespread in the Holarctic region (Fjeldså 1973a). The species is a broadly distributed but uncommon breeder in Eurasia, primarily between latitudes 50º N and 63º N (Balmer et al. 2013; Stedman 2020). It winters along seacoasts south to the Mediterranean Sea, with large concentrations in the Northeast Atlantic (Stedman 2020). In eastern Asia, it is present along the Pacific coast from Japan south to the Korean Peninsula (AOU 1998).

In North America, the Horned Grebe breeds across much of the northwestern portion of the continent, predominantly in Canada, with its core breeding range in the Prairie provinces and Northwest Territories. In the United States, it breeds in central and southern Alaska and, to a lesser extent, in several states bordering, or close to, western Canada, including Washington, Oregon (irregularly), Idaho, Montana, North Dakota, South Dakota (irregularly) and Minnesota (irregularly) (Stedman 2020). The species’ primary wintering grounds are the Pacific coast from British Columbia to northern Mexico (Baja California), the Atlantic coast from southern Nova Scotia and New Brunswick to Florida, and the Gulf Coastal Plain (Fink et al. 2020). A small number of birds overwinter in the Great Lakes region, mainly during mild winters, as well as in disjunct wintering areas in the central and southern United States (Figure 1; Fink et al. 2020). Most individuals winter on the Pacific (48%) and Atlantic (35%) coasts, with a low number (12%) in the Gulf Coastal Plain region and only 5% in the interior (Fink et al. 2020; ECCC 2022).

Canadian range

Approximately 92% of the North American breeding range of the Horned Grebe is in Canada. Breeding densities are highest in the Prairie Ecological Area, but the species is also found in the Boreal, Northern Mountain, Southern Mountain and Atlantic ecological areas (Figure 2) (COSEWIC 2009; Fink et al. 2020).

The Horned Grebe is common throughout southern Yukon, and is regularly found north to Old Crow Flats, but abundance decreases north of the Boreal Cordillera Ecozone (Sinclair et al. 2003). In the Northwest Territories, it is present throughout the boreal and subarctic regions, with the highest densities in the south (Stedman 2020). The species has also been observed in southern Nunavut, south of Arviat (Fink et al. 2020), although it is not clear whether the scarcity of observations is indicative of a lack of observers or low abundance. Recent extralimital nesting records from Charlton and Danby islands, in James Bay, Nunavut (Fink et al. 2020), indicate that nesting occurs periodically in this region.

In British Columbia, the Horned Grebe breeds in widely scattered locations east of the Coastal Mountains, with notable concentrations primarily limited to the Peace River Lowlands, and the Cariboo and Thompson-Nicola plateaus (Figure 2; Howie 2015).

The Horned Grebe is found in every natural region of Alberta, although it is most abundant in the grassland and parkland regions (Semenchuk 2007). It is widely distributed in Saskatchewan, especially in the Prairie Potholes and Boreal Taiga Plains bird conservation regions (BCRs), but is found in the highest densities in the south-central portion of the province (Figure 2; Birds Canada and Environment and Climate Change Canada 2020). The Horned Grebe occurs in all BCRs in Manitoba, but is heavily concentrated in the Prairie Potholes BCR in the southwest corner of the province (Figure 2; Mitchell 2018).

Figure 2. Horned Grebe (Podiceps auritus) breeding distribution and relative abundance during the breeding season (7 June to 27 July), based on eBird data from 2005 to 2020 (Fink et al. 2020). The darker red shading indicates higher population density.

In Ontario, the Horned Grebe is considered a rare, irregular breeder, occurring primarily in the extreme northwestern portion of the province (Hoar 2007). Historical observations in the Fort Severn region, on Hudson Bay, indicate that the species may nest irregularly in the Hudson Bay and James Bay regions.

In Quebec, the Horned Grebe nests annually in very low numbers on the Magdalen Islands, where breeding birds have been present since at least 1900 (COSEWIC 2009), and possibly much longer. It is most common in the northeastern portion of the archipelago, especially at Pointe de l’Est, Brion Island and Île du Cap aux Meules. Elsewhere in Quebec, the Horned Grebe is an irregular and extremely rare breeder. A recent breeding record in Saint-Bruno-de-Guigues from 2016 (Robert et al. 2019) indicates that the species may nest infrequently in portions of mainland Quebec, although this record was the first for mainland Quebec in “several decades” (Aubrey pers. comm. 2023). Several historical nesting occurrences have also been documented, and include 1919 on Anticosti Island (Lewis 1924), 1959 on Lake Saint-Anne (Ouellet and Ouellet 1963) and 1960 and 1964 on Lake Perceval at Valcartier (Larivée 2006). These records are thought to involve individuals from the Western subpopulation rather than the Magdalen Islands subpopulation (Shaffer 2019).

Low numbers of Horned Grebes remain in southern Canada in winter, primarily in southern British Columbia, southern Ontario and the Maritimes, but the majority overwinter along the Pacific and Atlantic coasts of the United States (Figure 1; Fink et al. 2020).

Population structure

See Designatable units, above.

Extent of occurrence and area of occupancy

The species’ extent of occurrence (EOO) was calculated as 5,003,843 km², obtained by drawing a minimum convex polygon around its full distribution in Canada. This differs from the EOO calculated in the previous status report (5,100,000 km² for the western DU; COSEWIC 2009), due to the difference in the number of Dus, with the Canadian population now comprising a single DU across the country rather than the two separate Dus mapped in the 2009 status report (COSEWIC 2009; see Designatable units, above). The geographic range of the Western subpopulation is currently estimated at 3.9 million km²; this differs from the 5.1 million km² calculated for the previous western DU (COSEWIC 2009), reflecting changes in methodology rather than changes in range. Details of distribution are insufficiently known to calculate the index of area of occupancy (IAO), but it is certainly far above COSEWIC’s minimum threshold of 2,000 km² for Threatened.

Biology and habitat use

The Birds of the World (formerly Birds of North America) account (Stedman 2020) provides the most comprehensive overview of Horned Grebe biology; only elements relevant to determining status are provided in the subsections below.

Life cycle and reproduction

The average lifespan of the Horned Grebe is not known; however, the oldest individual banded in North America was 5 years and 11 months old at recapture (Lutmerding and Love 2017). The species reaches sexual maturity at one year of age, but approximately 10% of all sexually mature individuals do not breed in a given year; non-breeding individuals primarily consist of second-year birds (Fjeldså 1973b). The generation length for the Horned Grebe has been estimated at 4.4 years, using modelled values of age‑of‑first‑breeding, maximum longevity and annual adult survival (Bird et al. 2020).

Horned Grebes nest on ponds, marshes and the bays of lakes. Small wetlands may support only one pair; occupancy of larger sites by multiple pairs is dependent on prey abundance and the availability of suitable nest sites (Fjeldså 1973c). Both members of the pair build the nest in a patch of emergent vegetation, using plants and flotsam gathered from the vicinity of the nest site (Ferguson 1977). Nests are most frequently attached to stalks of emergent vegetation and are floating, but may also be built on a solid base in shallow water. Less frequently, nests are located on rocks emerging from the water or on dry shorelines (Fjeldså 1973c; Ulfvens 1988; Stedman 2020). Over the course of the breeding season, additional vegetation may be added to the nest, particularly in response to increased water levels or wave action (Ulfvens 1988). Nests from the previous year are not known to be reused (Stedman 2020).

In North America, pair formation often begins in mid- to late winter and continues through spring migration until the pair arrives at the breeding site (Storer 1969). Pairs engage in elaborate bonding rituals that likely strengthen the pair bond (Storer 1969; Fjeldså 1973d; Stedman 2020). Construction of the nest begins shortly after birds arrive on the breeding grounds (Stedman 2020). There is generally one brood per year, but re-nesting is common if the first nest fails (Fjeldså 1973b). In Canada, the clutch of 5 to 7 eggs is generally laid between mid-may and mid-June (Ferguson and Sealy 1983; Arnold 1990). Eggs are incubated for 22 to 25 days, and hatch between mid-June and early August in Canada (Ferguson and Sealy 1983). Hatched young are semi-precocial, and able to swim and dive immediately after emergence from the egg; they are rarely brooded on the nest and are instead carried on the parents’ backs. Brooding lasts approximately 9 days and parents continue to consistently feed the young for up to 14 days following hatching (Stedman 2020). The young generally become fully independent at about 19 to 21 days after hatching; those that hatch later in the season take longer (21 to 24 days) to become independent. The first flights usually occur 41 to 50 days after hatching (Stedman 2020).

In Manitoba, the success rate of hatched eggs was 30.3%, with 72% of hatched young surviving to 10 days and pairs producing an average of 2.75 young annually (Ferguson and Sealy 1983). In Iceland and Norway, the success rate of hatched eggs was estimated at 63% and, in Finland, annual productivity ranged from 1.53 to 1.91 young per pair (Fjeldså 1973b; Ulfvens 1988, 1989). On the Magdalen Islands, the average clutch size is 4.4 eggs, with a hatching success rate of 54%; minimum annual productivity for this subpopulation is estimated at 0.6 young per pair based on observations of breeding pairs. Fall counts at the Étang de l’Est [East Pond] in the Magdalen Islands suggest productivity of approximately two young per pair, although this assumes that all immature birds observed in this pond are from the local breeding group (Shaffer and Laporte 2003).

Habitat requirements

Breeding habitat

In Canada, the Horned Grebe favours shallow freshwater ponds, marshes and the bays of lakes, small to medium in size (0.05 to 10 ha), with a mixture of emergent vegetation and open water. In some areas, alkaline or brackish water bodies are used (Stedman 2020). The species requires permanent water bodies, as they are used for both nesting and brood rearing (Sugden 1977; Ferguson and Sealy 1983). In Manitoba and Saskatchewan, ponds used by nesting Horned Grebes had a mean size of 1.2 ha ± 1.3 SD (Sugden 1977; Ferguson and Sealy 1983). The Horned Grebe requires a minimum water depth of 20 cm for breeding; the average depth of occupied ponds in Manitoba was 39.2 cm ± 11.7 SD, although deeper ponds were preferred in Saskatchewan (Ferguson and Sealy 1983). Emergent vegetation commonly associated with Horned Grebe nesting sites includes sedges (Carex spp.), rushes (Juncus spp.) and cattails (Typha spp.), which provide secure, concealed nest sites (Stedman 2020). Eutrophic wetlands are preferred but, when scarce, oligotrophic ponds are used (Ulfvens 1988). On the Magdalen Islands, Horned Grebes occupy similar wetland habitat, although ponds tend to be smaller (average 0.7 ha; n = 24) and deeper (89 cm; n = 26). The majority of occupied ponds are freshwater, but brackish sites are also sometimes selected (Shaffer and Laporte 2003).

On the Canadian prairies, breeding by the Horned Grebe has been well documented in constructed wetlands and borrow-pit ponds (Kuczynski and Paszkowski 2012). An Alberta survey of 330 borrow-pit ponds found that 36% were occupied by Horned Grebes (Kuczynski et al. 2012).

Migration habitat

During migration, Horned Grebes use coastal waters, lakes, rivers and marshes as stopover habitat (Stedman 2020). Spring and fall staging areas may be used annually, but the characteristics of these key sites are not well understood.

Wintering habitat

In North America, Horned Grebe wintering habitat has not been well studied, but is thought to consist primarily of inshore saltwater habitats, with medium to large freshwater water bodies used to a lesser extent (Stedman 2020). In Europe, large concentrations sometimes overwinter on the open sea, making these birds difficult to detect with regular survey methods (Stedman 2020).

Movement, migration, and dispersal

The Horned Grebe is a medium-distance migrant that primarily travels at night (Stedman 2020). Nocturnal migratory flights are likely completed in flocks, while diurnal migration is undertaken by individual birds or small loose groups swimming or flying over water (Palmer 1962; Potter 1974; Ulfvens 1988; Sibley 1997). The species’ migration routes are poorly understood, with most individuals moving over a broad front through the interior of North America and along the east and west coasts (Stedman 2020). Stopover and staging sites are not well known, but may be learned and used annually (Stedman 2020).

Spring migration takes place between mid-March and early may, depending on the overwintering location and the availability of open water (Small 1994; Stevenson and Anderson 1994; Peterjohn 2001). Initiation of fall migration is often weather-dependent and may be accelerated by the freezing of waterbodies (Stedman 2020). In fall, Horned Grebes begin to arrive on the northern Atlantic wintering grounds between mid- and late October and on the coast of Florida by mid-November (Stevenson and Anderson 1994). On the Pacific Coast, migrants arrive in coastal California between October and November (Small 1994). The Horned Grebe leaves the Magdalen Islands between late September and early October (Fradette 1992; Shaffer and Laporte 2003; Richard 2005). During nocturnal migration, inclement weather—particularly ice storms—has resulted in grounding and mortality events in the species (Hodgson 1979; Bell 1980; Eaton 1983).

Dispersal and site fidelity in adult and fledgling Horned Grebes is poorly understood, as studies of marked individuals have been limited. Young Horned Grebes typically leave their hatching sites once they are able to fly, approximately 41 to 50 days after hatching. Adults sometimes depart before the young are fully independent (Stedman 2020). Adults of both sexes demonstrate territorial fidelity, which may be correlated with reproductive success. Fidelity to nesting sites that were successful in previous years can result in the same pair reforming and a renewal of pair bonds (Ferguson 1981; Stedman 2020).

Interspecific interactions

Diet

Diet varies seasonally, and primarily includes aquatic insects, crustaceans and fish, with amphibians and other arthropods also taken (COSEWIC 2009). During the breeding season, aquatic invertebrates and some aerial insects comprise the majority of the diet (Stedman 2020). In winter, crustaceans (amphipods and crayfish in North America) and fish, consisting mostly of benthic species, dominate (Madsen 1957; Ainley and Sanger 1979). At all times of the year, locally abundant or superabundant prey are opportunistically exploited (Fjeldså 1973b).

Predators and competitors

The Horned Grebe is vulnerable to predation at all life stages, although particularly as an egg, hatchling, or incubating adult in the nest; predation is generally the primary cause of nest failure or loss (Ferguson and Sealy 1983; Fournier and Hines 1999; Stedman 2020). The American Mink (Neovison vison) has been recorded as a frequent predator of adults, particularly during incubation or brooding (Eberhardt and Sargeant 1977; Arnold and Fritzell 1990); other predators of adults include the Great Blue Heron (Ardea herodias), Domestic Cat (Felis catus), Gyrfalcon (Falco rusticolus), Northern Harrier (Circus hudsonius) and Red Fox (Vulpes vulpes) (Fjeldså 1973c; Bayer 1979; Hukee 2016; Stedman 2020). Other nest predators in North America include the Common Raccoon (Procyon lotor), American Crow (Corvus brachyrhynchos), Common Raven (Corvus corax), Black-billed Magpie (Pica hudsonia), American Coot (Fulica americana) and various gull species (Family Laridae; Ferguson and Sealy 1983; Stedman 2020). The predation of Horned Grebe eggs by Common Raccoons has been described as severe in southwestern Manitoba, where raccoons have become more abundant over the past 75 years (Hammell 2017). After leaving the nest, the young are also preyed on by gulls and Northern Pike (Esox lucius).

Horned Grebe pairs are highly territorial and aggressively defend their nesting and brooding habitat. Other grebe species are frequent targets, including the Pied-billed Grebe (Podilymbus podiceps), Red-necked Grebe and Eared Grebe, which breed sympatrically with the Horned Grebe in Canada. On the Magdalen Islands, Pied-billed Grebes have been observed to exclude Horned Grebes from the most suitable nesting habitats, since they arrive earlier in spring; at four ponds where both species were present early in the breeding season, only the Pied-billed Grebe was observed to have successfully nested (Shaffer and Laporte 2003; Environment Canada 2013). Larger grebe species have also been observed to exclude Horned Grebes from their preferred nesting habitat (Stedman 2020). Horned Grebes aggressively chase off waterfowl, Red-winged Blackbirds (Agelaius phoeniceus), Black Terns (Chlidonias niger) and even Muskrats (Ondatra zibethicus). In winter, Horned Grebes often associate with scoters (Melanitta spp.) and Common Loons (Gavia immer; Pearse 1950; Paulson 1969). The Horned Grebe competes for aquatic invertebrate prey with a variety of fish species, and may preferentially select fishless water bodies for nesting. The decline of breeding by Horned Grebes in agricultural areas in Scandinavia is thought to be closely linked to competition for food resources with an increasing cyprinid fish population (Douhan 1998).

Physiological, behavioural, and other adaptations

The Horned Grebe is an almost entirely aquatic species, able to move only short distances on land, and awkwardly at that (Fjeldså 1973c). Individuals fly primarily during migration, but also sometimes during the breeding season to seek mates, engage in territorial interactions with other Horned Grebes, and travel from wetland to wetland in the evening (Storer 1969). The Horned Grebe is highly territorial and engages in threat displays, as well as physical confrontations, with rival individuals (Fjeldså 1973d; Cramp and Simmons 1977).

The Horned Grebe has demonstrated some adaptability in its use of nesting habitat, readily using artificial wetlands, including borrow-pit ponds along road and highway corridors (Kuczynski et al. 2012; Kuczynski and Paskowski 2012). This may be a detriment in some situations, as the species has been observed in settling ponds containing contaminants that may negatively impact the species, such as detergents (see Threats - Pollution) (Nero 1963). The Horned Grebe does not adapt well to water-level fluctuations in its breeding ponds, and flooding, drought or alterations to hydrology may result in nest failure.

Limiting factors

The Horned Grebe’s high susceptibility to predation during nesting, particularly from other avian species and mammals, is a limiting factor (Stedman 2020).

As the Horned Grebe relies on aquatic invertebrates during the breeding season (Stedman 2020), prey abundance may also be limiting. Significant and pervasive declines have been observed in aquatic invertebrate populations in the Northern Hemisphere (Corcoran et al. 2009; Arzel et al. 2020).

Population sizes and trends

Data sources, methods, and uncertainties

Christmas Bird Count (CBC)

The Christmas Bird Count (CBC), established in 1900, documents winter bird populations annually in fixed 24-km-diameter count circles (Birds Canada 2020). The program provides population and abundance estimates for most wintering birds in Canada and the U.S., including the Horned Grebe. In each count circle, CBC volunteers record all bird species and individual birds observed on a single day between 14 December and 5 January of a given year.

CBC coverage of the Horned Grebe’s non-breeding range (Canada and the U.S.) was relatively limited until 1970. Trend analyses using data since 1970 were performed using an adjusted observation value for effort (birds per party hour). Given that few Horned Grebes overwinter in Canada, trends derived from CBC data in Canada may largely reflect fluctuations at the northern edge of the wintering range and CBC trends at the North American scale should be more reflective of the Canadian population, given that Canada accounts for about 92% of the continental breeding range.

North American Breeding Bird Survey (BBS)

The Breeding Bird Survey (BBS) is designed to detect breeding bird species through standardized roadside surveys conducted primarily by volunteers. In Canada, it is coordinated by the Canadian Wildlife Service. The program began in 1966 and is the primary source of data for assessing long-term, large-scale population changes in over 400 breeding bird species in Canada and the United States. Surveys are run along 39.2-km routes comprising 50 stops spaced 0.8 km apart. Data on breeding birds are recorded at each of the 50 stops, with observers noting the total number of individuals of all bird species heard from any distance or visually observed within 0.4 km of each stop during a three-minute observation period (Government of Canada 2019).

In Canada, BBS data provide extensive, long-term survey information on the Horned Grebe, although coverage is heavily skewed toward the Prairie portion of the breeding range, with relatively few routes in the more northern part. The resulting trends may therefore reflect a regional bias. The primary advantage of the BBS is that data are gathered annually following a standardized survey protocol. However, as the Horned Grebe is not particularly vocal, detectability is likely to be limited primarily to stops with a good roadside view of breeding wetlands.

Breeding bird atlases

Several provincial breeding bird atlas projects have been completed since 2009, in British Columbia (2008 to 2012), Saskatchewan (2017 to 2022), Manitoba (2010 to 2014) and Quebec (2010 to 2014), providing important regional contributions to the provincial population estimates for the Horned Grebe. The second Quebec atlas has proven particularly useful, in that the results can be compared to those from the first Quebec atlas, undertaken in 1984 to 1989.

Abundance

The Canadian population of the Horned Grebe is estimated to number from 200,000 to 500,000 individuals (BirdLife International 2020; Wetlands International 2020). The previous estimate was 100,000 to 1,000,000 individuals (COSEWIC 2009); the new range reflects a refinement of calculation methods (BirdLife International 2020; Wetlands International 2020).

The highest breeding densities occur in the Parkland zone of the Prairie provinces (Fink et al. 2020), with an estimated 1.5 to 3.3 pairs per km² (Sugden 1977). Similarly high densities are also estimated to occur in portions of the species’ boreal range, with an average of 2.2 pairs per km² observed in the area surrounding Yellowknife, although this may be related to the presence of human-made ponds in these areas, since densities were lower in natural ponds east of Yellowknife (average of 0.5 pairs per km²) (Fournier and Hines 1999). While no large-scale studies or estimates have been completed in the northern portion of the Canadian breeding range, the existing data tend to suggest that Horned Grebe breeding densities are generally lower there (Howie 2015; Mitchell 2018; Birds Canada and Environment and Climate Change Canada 2020; ECCC 2022). According to Stedman (2020), the highest densities in the Northwest Territories occur in the southern portion.

Fluctuations and trends

Christmas Bird Count (CBC)

At a North American scale, point estimates using CBC data indicate a long-term increase of 0.38% per year (95% credible interval [CI] = -0.54, 1.59) from 1970 to 2021, amounting to an estimated overall increase of 21.3%, although the credible intervals are very wide (95% CI = -24.1, 123.6). Higher estimates were obtained for the most recent three-generation period (2008 to 2021; 1.23% per year, 95% CI = -3.22, 5.88), equivalent to 17.2% over that time period, although these estimates are also highly imprecise (95% CI = -34.7, 110.2; Figure 3; Meehan pers. comm. 2022). The CBC data point to a steady increase in wintering numbers along much of the Pacific coast since the 1970s, but a long-term decline on the Atlantic coast; however, numbers in the latter have increased since around 2005 relative to levels in the 1980s (Roy unpubl. data 2019; ECCC 2022). Trends in the northwest, where the species is most abundant, are positive (and drive the positive continental trend), as they are in the Great Lakes, Ozarks and Mid-Atlantic regions, while they are negative elsewhere in the wintering range (Figure 3; Meehan pers. comm. 2022).

Figure 3. Christmas Bird Count three-generation (2008 to 2021) grid-level results for the (A) annual change in abundance and (B) relative abundance of the Horned Grebe (Podiceps auritus) (T. Meehan unpubl. data 2022).

North American Breeding Bird Survey (BBS)

BBS data indicate long- and short-term declines in the Horned Grebe population in Canada (Smith unpubl. data 2020; Figure 4; Table 1). During the 1970 to 2019 period, the average annual trend was -1.71% (95% CI = -4.56, 0.67), amounting to a cumulative trend of -57.0% (95% CI = -89.9, 38.7). Over the most recent three generations (2006 to 2019), the national rate of change is estimated at -1.11% per year (95% CI = -6.05, 4.54), equivalent to -13.5% cumulatively (95% CI = -55.5, 78.0). At a regional scale, cumulative three-generation trend estimates are particularly negative in British Columbia (cumulative change of -46.8%; 95% CI = -98.1, 44.5) and Manitoba (-34.2%; 95% CI = -76.3, 41.6), and were positive only in Yukon (0.2%; 95% CI = -57.0, 173.6) and Alberta (29.1%; 95% CI = -29.2, 160.0) (Figure 5; Table 1). However, the reliability of all short-term trends is deemed low (Table 1). Wetter conditions in the Prairies in recent years may have been favourable for the Horned Grebe, as there appears to be a strong correlation between the number of breeding ponds present in these areas in may and the number of Horned Grebes recorded during BBS surveys (ECCC 2022). It is also possible that, in drier years, Horned Grebes may overfly these areas to find suitable ponds elsewhere, presumably farther north (ECCC 2022). Given the bias in BBS coverage towards the southern portion of the Canadian breeding range, this variability may affect the proportion of the population sampled from year to year.

Figure 4. Annual index of abundance for the Western subpopulation of the Horned Grebe (Podiceps auritus) in Canada, based on Breeding Bird Survey data from 1970 to 2019 (n = 910 routes), with the blue dots indicating observed means. The GAM (generalized additive model) trend in orange represents the best curvilinear fit of data, whereas the slope trend in blue incorporates effects of annual variations. Orange (appearing grey in areas of overlap) and blue shading show 95% credible intervals for the GAM and slope trends, respectively. Green bars indicate the number of survey routes in Canada with Horned Grebe detections (A. Smith unpubl. data 2020).

Figure 5. Annual rates of Horned Grebe (Podiceps auritus) population change estimated over three generations (2006 to 2019) from Breeding Bird Survey trends at the scale of Bird Conservation Regions within provinces, territories, and states (A. Smith unpubl. data 2020).

The national rolling trend shows an ongoing decline spanning several decades, but with minimal changes over the past three generations (Figure 6). However, it is apparent that there is broad uncertainty surrounding the annual indices, and short-term changes may be more substantial in either direction.

Figure 6. Rolling 13-year (three-generation) trends in changes in the Horned Grebe (Podiceps auratus) population in Canada, based on Breeding Bird Survey data from 1970 to 2019 for the Western subpopulation (A. Smith unpubl. data 2020). The vertical axis represents the average annual percent change in population size over a three-generation period. The horizontal axis represents the last year of the 13-year rolling trend (for example, 2019 is the trend for 2006 to 2019). The orange and red horizontal lines depict the 30% and 50% cumulative short-term decline rates, which represent the COSEWIC thresholds for listing a species as Threatened and Endangered, respectively. The vertical bars represent the 50% (broad, dark blue) and 95% (narrow, light blue) credible intervals.

Other information sources

The British Columbia Coastal Waterbird Survey (Birds Canada 2023), a citizen science project aimed at providing data from early December to early February on coastal waterbird trends, documented a statistically significant decrease in the species in the Salish Sea of -2.60% per year (1999 to 2011; Crewe et al. 2012); however, over a longer period (1999 to 2019), it showed stabilizing numbers or possibly an increase in numbers in the Salish Sea and outer Pacific Coast (annual trends: 1.51; 95% CI = -2.18, 4.92; and 6.40; 95% CI = -2.57, 15.26, respectively; Ethier et al. 2020). The inter-regional movement of birds could not be ruled out as the cause of these trends (Ethier et al. 2020)

In contrast, the eBird trend map for the Horned Grebe released in November 2022 shows consistent and significant declines in excess of 30% across the wintering range over the last three generations (28 December to 8 February, 2007 to 2020; Fink et al. 2022; Figure 7). Trends are estimated for 27 km x 27 km cells and, like the CBC, the breadth of the Canadian population is sampled. In addition, no cells with significant trends show positive values. However, range-wide estimates are not yet available for these analyses.

A study in southwestern Manitoba documented a decline in breeding Horned Grebe population density at two sites, from 1.0 to 1.3 birds/km² in the 1970s to 0 to 0.6 pairs/km² in most years in the 2000s (Hammell 2017).

Although breeding bird atlas data are available for several provinces, only Ontario and Alberta have two atlases that would allow for comparison of trends, and the latest observations for these atlases date back to 2001– 2005, which does not provide an insight into recent trends.

Figure 7. Horned Grebe (Podiceps auritus) trends in the non-breeding season (28 December–8 February), 2007 to 2020. The cumulative change in estimated relative abundance in 27 km x 27 km cells is depicted; the cell sizes on the map are scaled by the estimated relative abundance in the middle year of the range (2014). The red circles show declines and the blue circles show increases (there are no circles with increasing trends for this species), with darker colours representing stronger trends. Source: Fink et al. 2022.

Summary

The most extensive data on Horned Grebe population trends are those from the BBS and CBC. Although BBS data provide direct information on breeding population trends in Canada, the national trend estimate is driven primarily by observations from the Prairies, where most routes that detect the species occur. However, these trends provide little insight into more northern breeders. However, continental CBC trends should largely reflect the Canadian population as a whole, given that 92% of the range of the North American population occurs in Canada, and most individuals that breed in Canada winter in the United States.

The contrast in trends (the increase inferred from the North American CBC versus the decline inferred from the Canadian BBS) suggests that the Prairie-breeding portion of the population, which is exposed to a greater variety of threats, may be declining, but at a rate that appears to be offset by an increase in breeding numbers in more northern areas. However, limited BBS data from Yukon and the Northwest Territories suggest stable to declining trends, so at least some parts of the northern range are showing decreasing numbers (Table 1; Figure 5), an interpretation supported by the recent trend estimates derived from eBird data (Fink et al. 2022).

Severe fragmentation

The Magdalen Islands subpopulation is disjunct, occurring > 2,000 km from the nearest regularly occurring part of the Western subpopulation, in northwestern Ontario (Figure 1). This is not equivalent to “severely fragmented”; see definition in Technical Summary, Box 11.

Rescue effect

The immigration of Horned Grebes breeding in the United States to Canada is undocumented, but considered possible. The breeding habitat in Canada is very similar to that used by birds in the U.S. and there are no substantial climate differences. Despite the potential for immigration, Canada accounts for about 92% of the range of the North American population. Therefore, the potential for rescue from the U.S. population is considered to be unlikely.

Threats

Historical, long-term, and continuing habitat trend

Water-level fluctuations, increased temperatures and agricultural land conversion are the three main drivers affecting the breeding habitat of the Horned Grebe. Changes in water levels due to drought are believed to have negatively impacted the population in the late 1990s and early 2000s (ECCC 2022). However, the increase in precipitation from 2005 to 2022 is postulated to have benefitted the species, accounting for the apparent recent population increases (ECCC 2022). Agricultural conversion is accompanied by the draining of wetlands (Sugden and Beyersbergen 1984; COSEWIC 2009). In some areas, up to 70% of wetlands have disappeared since European settlement (Watmough et al. 2017; Benalcazar et al. 2019; DUC 2021). It is estimated that 75% of Prairie pothole wetlands have been drained or converted to agricultural use (Benalcazar et al. 2019). In the Prairie region, more than 90% of wetlands show signs of alteration, and the number of remaining unaltered wetlands in the landscape is decreasing (Environment Canada 2013).

Current and projected future threats

The Horned Grebe is vulnerable to the cumulative effects of various threats throughout its life cycle. These are categorized below and in Appendix 1, following the IUCN-CMP (International Union for the Conservation of Nature – Conservation Measures Partnership) unified threats classification system (based on Salafsky et al. 2008).

The evaluation assesses impacts for each of 11 main categories of threats and their subcategories, based on the scope (proportion of population exposed to the threat over the next 10-year period), severity (predicted population decline among those exposed to the threat, during the next 13 years = 3 generations) and timing of each threat. Scores and supporting information have been adapted from the proposed management plan for the Western population (ECCC 2022) and the recovery strategy for the Magdalen Islands population (EC 2013).

The overall threat impact is calculated by taking into account the separate impacts of all threat categories (Master et al. 2012). For the Horned Grebe, the overall threat impact is assessed as Medium, meaning that declines of 3% to 30% are anticipated over the species’ next three generations.

IUCN 2, agriculture and aquaculture (low threat impact)

IUCN 2.1, annual and perennial non-timber crops

Historically, the draining of natural wetlands in the Canadian Prairies for conversion to agriculture has significantly reduced the availability of suitable breeding habitat for the Horned Grebe. In Canada, an estimated 70% of historical wetlands have been lost or degraded since European settlement, while nearly 75% of Prairie pothole wetlands have been converted to agriculture (Sugden and Beyersbergen 1984; Bartzen et al. 2010; Benalcazar et al. 2019; DUC 2021). Of the remaining wetlands in the Prairie region, over 90% have been altered or degraded (Environment Canada 2013). The Horned Grebe prefers breeding in wetlands between 0.1 ha and 1.25 ha in size. However, many of the remaining natural wetlands in the Prairies are too large to be suitable, as optimal pothole‑type wetlands have largely been lost in more developed areas (Kuczynski et al. 2012). According to estimates by Ducks Unlimited Canada, between 6 ha and 8 ha of wetland habitat continue to be lost daily in Manitoba and Saskatchewan alone (Benalcazar et al. 2019; DUC 2021).

IUCN 3, energy production and mining (low threat impact)

IUCN 3.1, oil and gas drilling

Development and expansion of oil and gas extraction and processing facilities is prevalent in portions of the western boreal forest and the Prairies, often overlapping with areas used by the Horned Grebe during the breeding season. A considerable amount of infrastructure is required for these industries, including roads, pipelines and tailing ponds, all of which can lead to the alteration and removal of wetlands (PHJV 2014). However, wetlands in these areas are afforded some level of protection by industry best-management practices, and provincial and federal policies that protect wetlands from removal for development or mitigate the impacts of development. Despite these practices, some loss of wetland extent and function occurs. The small, shallow, fishless water bodies and pothole wetlands that breeding Horned Grebes prefer may be overlooked during the environmental studies undertaken for these developments, due to the large scale of the projects and the perceived lesser significance of small wetlands when compared to larger wetland complexes and water bodies (ECCC 2022).

IUCN 3.3, renewable energy

Collisions between Horned Grebes and wind turbines have been recorded in Canada (Environment Canada 2013). Grebes in general are considered to be particularly susceptible to collisions with wind turbines, because they are nocturnal migrants, fly at low altitudes, and have limited manoeuvrability (Furness et al. 2013; Stedman 2020). Solar farms can also pose a threat to Horned Grebes and other waterbird species. Birds may mistake the reflective solar panels for water bodies and land on them; because grebes have difficulty taking off from land, they may become stranded and die from starvation or predation (Kagan et al. 2014). Individuals from both subpopulations are most likely to encounter these threats during migration.

In addition, similarly to what was described under IUCN 3.1, the continued construction of wind turbine and solar farms in the Prairie region may result in the removal of wetlands used by nesting Horned Grebes.

IUCN 4, transportation and service corridors (low threat impact)

IUCN 4.2, utility and service lines

Grebes are particularly vulnerable to collisions with power lines, due to their low flight altitude, limited manoeuvrability and nocturnal migratory behaviour (APLIC 2012; Environment Canada 2013; Rioux et al. 2013; Stedman 2020). Although most grebes encounter power lines at some point in their life, only a small minority of them experience collisions. However, considering the documented vulnerability of grebes to power line collisions and the likelihood that mortality is somewhat underestimated given that not all carcasses are detected or identified, the severity of the threat at the population scale may be as great as Slight (1 to 10%). No estimated rates of collision specific to the Horned Grebe are available.

IUCN 5, biological resource use (low threat impact)

IUCN 5.1, hunting and collecting terrestrial animals

Hunting bycatch of the species may occur, given that a large part of the population likely migrates through areas where waterfowl hunting occurs. The Magdalen Islands subpopulation is vulnerable to hunting bycatch and indiscriminate shooting and hunting, as waterfowl hunting occurs in late autumn at Étang de l’Est, where the majority of Magdalen Islands Horned Grebes moult (Shaffer and Laporte 2003). Additionally, at least one female was shot in June 2014 while on a nest, and another individual was found dead along a road in 2011, also believed to have been shot (Shaffer pers. comm. 2020). However, there is little evidence (anecdotal or otherwise) overall to suggest that this is a widespread concern for the species during any part of its annual cycle, and the overall severity is rated Negligible.

IUCN 5.4, fishing and harvesting aquatic resources

During migration and on the wintering grounds, the Horned Grebe feeds primarily on a variety of fish species, which, in some areas, puts individuals at risk of accidentally being caught in fishing nets and drowning (Riske 1976; Piersma 1988; Ulfvens 1989; Harrison and Robins 1992). Accidental bycatch of grebes and other diving waterbirds has been reported on the Great Lakes during migration (COSEWIC 2009), as well as on Lake Winnipegosis, Manitoba, where an estimated 3,000 grebes and loons were reported to be netted annually in the southern part of the lake (Bartonek 1965). Little evidence of accidental take of Horned Grebes has been reported on the Atlantic and Pacific coasts in Canada; however, gill-net fishing for salmon on the Pacific Coast was estimated to be responsible for the death of 12,085 (range 1,129 to 24,002) seabirds every year (Smith and Morgan 2005). Although not well reported, it is likely that at least some Horned Grebe mortality also occurs due to coastal fisheries. Other species of grebe have been reported in low numbers as bycatch in salmon gill-net fisheries on Canada’s Pacific coast (Bertram et al. 2021), while in the Baltic and North Seas of Europe, the Slavonian Grebe has been reported as incidental bycatch (Žydelis et al. 2009). The overall mortality from, and the severity of, this threat are likely toward the lower end of Slight.

IUCN 7, natural system modifications (low threat impact)

IUCN 7.1, fire and fire suppression

Fire has a significant impact on the ecology of the boreal forest, contributing to habitat loss and regeneration, the alteration of vegetation composition, increased sedimentation, and changes in the nutrient cycle and hydrology. The effects of climate change are expected to result in an increase in the fire season length, as well as in the annual area burned and the number of large forest fires (Amiro et al. 2003; Natural Resources Canada 2020). No information is available on the direct impacts of forest fires on the Horned Grebe, but potential effects include the loss of suitable nesting habitat, contamination of wetlands and a decrease in reproductive success (Environment Canada 2013). Additional research is necessary to understand the impact of forest fires on waterbirds and the wetland habitats they occupy during the breeding season.

IUCN 7.3, other ecosystem modifications

The Horned Grebe is vulnerable to changes in water quality and depth, as it relies on aquatic habitats for nearly all of its life functions. These changes have the greatest impact on the small, shallow wetlands that Horned Grebes use during the breeding season. Water quality and depth can be affected by a wide range of human activities, including agriculture, ranching and livestock farming, oil and gas extraction, mining and quarrying, logging, and infrastructure-related construction. These types of activities are common throughout the species’ breeding range and can increase nutrient loading and sedimentation in wetlands (Bayley et al. 2013). These effects can alter water flows, nutrient dynamics and aquatic and riparian vegetation.

Horned Grebes prefer eutrophic wetlands for breeding in the short term, as nutrient loading can increase the abundance of macroinvertebrate prey (ECCC 2022). However, long-term eutrophication decreases water quality, increases emergent and submerged aquatic vegetation growth, and causes greater turbidity (Scheffer et al. 2001; Bayley et al. 2013). These factors may make foraging more difficult for the Horned Grebe, and decrease the availability of open water, potentially rendering small wetlands unsuitable for breeding. Similarly, sedimentation resulting from human activities can increase water turbidity and decrease wetland depth; given that Horned Grebes prefer small, shallow water bodies, this may decrease depth to the point of wetlands being unsuitable or lost entirely (Bayley et al. 2013). Invasive plants such as European Common Reed (Phragmites australis ssp. australis) and Purple Loosestrife (Lythrum salicaria) that form dense stands may also reduce the suitability of wetlands for nesting Horned Grebes (Catling and Mitrow 2011; MNRF 2018).

Agricultural herbicides and pesticides are likely to contaminate some wetlands through surface runoff, leaching, spray drift and wind erosion. Atrazine and glyphosate are among the herbicides that have been documented in Prairie pothole wetlands (Environment Canada 2013). Glyphosate has been shown to pose a risk to freshwater algae and plants, as well as to marine and estuarine invertebrates (Pest Management Regulatory Agency 2017). The loss of freshwater plants in wetlands occupied by breeding Horned Grebes may make these wetlands less suitable for the species. Neonicotinoids, such as imidacloprid and fipronil, are now also widely used on the Prairies (Environment Canada 2013; Main et al. 2014; Douglas and Tooker 2015). Neonicotinoids can remain in soils for years and are highly soluble, resulting in a propensity to be washed into aquatic habitats (Main et al. 2014). These pesticides are known to have negative impacts on aquatic invertebrates (Van Dijk et al. 2013; Douglas and Tooker 2015). Macroinvertebrate abundance, particularly that of emergent aquatic insects, has been shown to consistently decline along a gradient of increasing imidacloprid concentrations (Van Dijk et al. 2013; Morrissey et al. 2015; Maloney et al. 2018).

IUCN 9, pollution (low threat impact)

IUCN 9.2, industrial and military effluents

The Horned Grebe is potentially vulnerable to contaminant spills. Tailings ponds associated with mining and oil extraction operations have been identified as posing a significant mortality risk to birds (Timoney and Ronconi 2010). The Oil Sands Bird Contact Monitoring Program was established in 2011 to estimate the number of birds landing on the tailings ponds of oil sands mines in Alberta (St. Clair 2014). The Horned Grebe was reported to land on tailings ponds with variable frequency between 2011 and 2018: on average 145 individuals per year (range 1 to 236; Canadian Natural Resources Limited et al. 2019). Despite the number of these incidents, relatively few Horned Grebes were oiled and died (Canadian Natural Resources Limited et al. 2019). Data are scarce on the non-lethal effects on surviving birds, although minor amounts of feather oiling can be lethal to waterbirds or cause sublethal health effects (Morandin and O’Hara 2016).

Oil spills are a threat to Horned Grebes on their wintering grounds, and may affect the long-term suitability of these areas as habitat. A 1976 oil spill in Chesapeake Bay resulted in the deaths of over 4,000 Horned Grebes (Roland et al. 1977). Data from eight oil spills in the southern U.S. indicate that Horned Grebes comprised 12.3% of 34,717 oiled birds killed (del Hoyo et al. 1992). Horned Grebes wintering along the Pacific coast are also threatened by oil spills; the Exxon Valdez oil spill in 1989 in Alaska resulted in declines in wintering numbers, which did not rebound to expected densities even years after the spill (Day et al. 1997; McKnight et al. 2008). However, the species’ broad winter distribution provides a buffer to some extent against the effects of localized oil spills (Stedman 2020).

The Horned Grebe is also vulnerable to the bioaccumulation of contaminants. DDE (dichlorodiphenyldichloroethylene) and PCBs (polychlorinated biphenyls) have been reported in Horned Grebe eggshells in Manitoba (Forsyth et al. 1994), and high levels of dioxins and furans were detected in the livers of Horned Grebes sampled downstream of a pulp and paper plant in British Columbia (Vermeer et al. 1993). The presence of contaminants (type and quantity) is expected to vary depending on where individual Horned Grebes overwinter.

A case of poisoning from lead shot was noted in a Horned Grebe on the Magdalen Islands in 1995 (Shaffer and Laporte 2003). However, it is difficult to know, based on only one case, whether this occurs more frequently. Since 1997, enforcement of the regulation banning the use of lead shot within 200 m of any watercourse during the waterfowl hunt has likely contributed to reducing this risk (Environment Canada 2013).

IUCN 9.3, agricultural and forestry effluents

The impact of the agricultural use of fertilizers on habitat and invertebrate prey is addressed under threat 7.3 (Other Ecosystem Modifications). The potential for toxicity through ingestion of pesticides is discussed here. The direct impacts of pesticides on the Horned Grebe have not been documented, but a potential sublethal effect occurs through a decrease in reproductive output (Environment Canada 2013; Van Dijk et al. 2013; Douglas and Tooker 2015).

IUCN 11, climate change (low threat impact)

IUCN 11.4, changes in precipitation and hydrological regimes

The impact of climate change on the Horned Grebe is poorly understood, with considerable uncertainty on how the species’ habitat and biology will be impacted by a warming climate and altered precipitation patterns and timing. Some predictions can be made based on the current understanding of the Horned Grebe’s requirements and life processes and the projected effects of climate change, as well as impacts that have already been observed and studied.

Bird species that breed in freshwater wetlands are particularly vulnerable to climate change impacts, as an increased deficit in precipitation relative to evapotranspiration is projected (Steen et al. 2014). In the Prairie pothole region, where much of the Horned Grebe population breeds, the relatively shallow, permanent wetlands preferred by birds are expected to be particularly vulnerable to these changes (Steen et al. 2014). How climate change will impact wetland habitats across Canada is still a subject of considerable uncertainty; however, some cumulative impacts are foreseeable (ECCC 2022). It is anticipated that a warmer climate with altered precipitation patterns will result in an increase in the number and severity of forest fire events. It is also expected that warmer temperatures will result in the melting of permafrost and the drying out of wetlands (Cheskey et al. 2011). In the short term, the melting of permafrost may increase the availability of open surface water for the Horned Grebe, but these benefits are expected to be short-lived and are speculative.

IUCN 11.5, severe / extreme weather events

Heavy rain and high waves combined with strong winds can contribute to the submerging of Horned Grebe nests (Shaffer and Laporte 2003). Conversely, long dry spells can reduce water levels and make ponds shallow and unsuitable for nesting. Later in the season, occupied nests are also more vulnerable to predation by land mammals during dry spells (Shaffer and Laporte 2003). During migration, storms or thunderstorms can cause the death of individual Horned Grebes (Hodgson 1979; Bell 1980; Eaton 1983). Given the small size of the Magdalen Islands subpopulation, Horned Grebes there are particularly vulnerable to extreme weather events.

Horned Grebes on the coastal wintering grounds may be affected by increases in the intensity of the El Niño-Southern Oscillation (ENSO), as well as changes to ocean temperatures and currents. These climate variations have the potential to affect the availability of the species’ food resources on its wintering grounds (Butler and Taylor 2005). During ENSO years, some seabirds have higher mortality than during non-ENSO years (Butler and Taylor 2005). Little is known about whether ENSO intensity affects the survival of wintering Horned Grebes.

Number of threat locations

The Horned Grebe is widely distributed in Canada, with most birds breeding in agricultural areas of the Prairies, where the greatest threats stem from agricultural land use and water management practices. As these are under the control of many individual land managers, there are likely hundreds or thousands of threat-based locations in Canada.

Protection, status, and recovery activities

Legal protection and status

In Canada, the Horned Grebe and its nest and eggs are afforded protection under the Migratory Birds Convention Act, 1994 (Government of Canada 2017). The Horned Grebe is listed as Endangered (Magdalen Islands population) and Special Concern (Western population) under Schedule 1 of the Species at Risk Act. In Quebec, this species has been listed as Threatened since 2000 under the Act Respecting Threatened or Vulnerable Species (CQLR, c E-12.01), and is afforded protection under the Act Respecting the Conservation and Development of Wildlife (CQLR c C-61.1), which also protects its Magdalen Island habitats.

In December 2023, COSEWIC combined the Magdalen Islands population and the Western population in a single unit across the Canadian range, and designated it as Special Concern.

The species is not protected under the Endangered Species Act in the United States (USFWS 2020), but is protected under the Migratory Bird Treaty Act (USC 1918).

Non-legal status and ranks

The Horned Grebe is considered globally Secure (G5; Table 2; NatureServe 2020). IUCN considers it to be Vulnerable (BirdLife International 2020). In Canada, the Horned Grebe is ranked Secure (N5B, N4N5N; NatureServe 2020) and Apparently Secure (S4B) in much of its Canadian breeding range (Y.T., B.C., Alta.), Secure (S5B) in Saskatchewan, Vulnerable (S3B) in N.W.T. and Manitoba, and Critically Imperiled in Ontario. Non-breeding birds are listed as Apparently Secure (S4B) Non-breeding in the Pacific and Atlantic oceans, and Vulnerable Non-breeding (S3N) in Ontario, Nova Scotia, and New Brunswick. In Quebec, the Horned Grebe is ranked as Vulnerable on migration (S3M), while the Magdalen Islands subpopulation has the rank of S1B (Critically Imperiled Breeding; CESCC 2020; NatureServe 2020; Table 2).

In the United States, the Horned Grebe is considered Secure (N5B; NatureServe 2020; see Table 2 for state-specific ranks).

Three Important Bird Areas (IBAs) are known to support important concentrations of the Horned Grebe: the Île de l’Est and Île Brion IBAs for the Magdalen Islands subpopulation, and the Prince Edward County South Shore IBA for the Western subpopulation.

Land tenure and ownership

The Horned Grebe breeds extensively on both privately owned and public lands. Parks Canada considers the species to be present at 29 sites (national parks, national park reserves, national historic sites and national marine parks). It is also likely present at many provincial parks, conservation areas, nature reserves and other public lands across Canada.

Recovery activities

Both a recovery strategy (Environment Canada 2013) and an action plan (Environment Canada 2015) have been produced for the Magdalen Islands population (now subpopulation), outlining the strategies in place and those to be implemented. A proposed management plan for the Western population (now subpopulation) of Horned Grebe has also been developed (ECCC 2022). The outlined or proposed actions have either not been realized or it is too soon to discern an impact.

Information sources

Ainley, D.G., and G.A. Sanger. 1979. Trophic relationships of seabirds in the northeastern Pacific Ocean and Bering Sea. Pp. 95-122, in J.C. Bartonek and D.N. Nettleship (eds.). Conservation of Marine Birds of Northern North America, U.S. Fish and Wildlife Service, Wildlife Research Reports 11.

Amiro, B.D., M.D. Flannigan, B.J. Stocks, J.B Todd, and B.M. Wotton. 2003. Boreal forest fires: an increasing issue in a changing climate. Paper submitted to the XII World Forestry Congress, 2003. Website: http://www.fao.org/3/XII/0207-B3.htm [accessed August 2021].

AOU (American Ornithologists’ Union). 1998. Checklist of North American Birds, 7th edition. American Ornithologists’ Union, Washington, D.C.

APLIC (Avian Power Line Interaction Committee). 2012. Reducing avian collisions with power lines: The state of the art in 2012. Edison Electric Institute and APLIC, Washington, D.C.

Arnold, T.W. 1990. Determinacy of clutch size in Horned and Pied-billed grebes. Wilson Bulletin 102:336-338.

Arnold, T.W., and E.K. Fritzell. 1990. Habitat use by male mink in relation to wetland characteristics and avian prey abundance. Canadian Journal of Zoology 68:2205‑2208.

Arzel, C., P. Nummi, L. Arvola, H. Pöysä, A. Davranche, M. Rask, M. Olin, S. Holopainen, R. Viitala, E. Einola, and S. Manninen-Johansen. 2020. Invertebrates are declining in boreal aquatic habitat: The effect of brownification? Science of the Total Environment 724:1-6.

Aubry, Y., pers. comm. 2023. Email correspondence to L. Blight. November 2023.

Balmer, D.E., S. Gillings, B. Caffrey, R.L. Swann, I.S. Downie, and R.J. Fuller. 2013. Bird Atlas 2007 to 11: The Breeding and Wintering Birds of Britain and Ireland. British Trust for Ornithology, Thetford, United Kingdom.

Bartonek, J.C. 1965. Mortality of diving ducks on Lake Winnipegosis through commercial fishing. Canadian Field-Naturalist 79:15-20.

Bartzen, B.A., K.W. Dufour, R.G. Clark, and F.D. Caswell. 2010. Trends in agricultural impact and recovery of wetlands in prairie Canada. Ecological Applications 20:525‑538.

Bayer, R.D. 1979. Great Blue Heron attacks Horned Grebe. Bird-Banding 50:264-265.

Bayley, S.E., A.S. Wong, and J.E. Thompson. 2013. Effects of agricultural encroachment and drought on wetlands and shallow lakes in the Boreal Transition Zone of Canada. Wetlands 33:17-28.

Bell, R.K. 1980. Horned Grebes forced down by ice storm. Redstart 47:142-144.

Benalcazar, P., V. Kokulan, A. Lillo, and J.-P. Matteau. 2019. The contribution of wetlands towards a sustainable agriculture in Canada. The Canadian Agri-Food Policy Institute, Ottawa, Ontario.

Bertram, D.F., L. Wilson, K. Charleton, A. Hedd, G.J. Robertson, J.L. Smith, K.H. Morgan, and X.J. Song. 2021. Modelling entanglement rates to estimate mortality of marine birds in British Columbia commercial salmon gillnet fisheries. Marine Environmental Research 166:105268.

Bird, J.P., R. Martin, H.R. Akçakaya, J. Gilroy, I.J. Burfield, S. Garnett, A. Symes, J. Taylor, C.H. Şekercioğlu, and S.H.M. Butchart. 2020. Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology 34:1252-1261.

BirdLife International. 2020. Species factsheet: Podiceps auritus. Website: http://www.birdlife.org [accessed January 2021].

Birds Canada. 2020. Christmas Bird Count. Website: s Bird Count. https://www.birdscanada.org/bird-science/christmas-bird-count/ [accessed January 2021].

Birds Canada. 2023. BC Coastal Waterbirds Survey. Website: https://www.birdscanada.org/bird-science/british-columbia-coastal-waterbird-survey [accessed 7 February 2023].

Birds Canada and Environment and Climate Change Canada. 2020. Saskatchewan Breeding Bird Atlas: 2017-2021. Website: https://sk.birdatlas.ca/about-the-atlas/ [accessed January 2021].

Bishop, L.B. 1889. Notes on the birds of the Magdalen Islands. The Auk 6:144-150.

Boulet, M., C. Potvin, F. Schaffer, A. Breault, and L. Bernatchez. 2005. Conservation genetics of the threatened horned grebe (Podiceps auritus L.) population of the Magdalen Islands, Quebec. Conservation Genetics 6:539-550.

Butler, R.W., and W. Taylor. 2005. A Review of Climate Change Impacts on Birds. USDA Forest Service General Technical Reports. PSW-GTR-191:1107-1109.

Cadman, M.D., D.A. Sutherland, G.G. Beck, D. Lepage, and A.R. Couturier (eds.). 2007. Atlas of the Breeding Birds of Ontario, 2001-2005. Bird Studies Canada, Environment Canada, Ontario Field Ornithologists, Ontario Ministry of Natural Resources, and Ontario Nature, Toronto, Ontario. xxii + 706 pp.

Canadian Natural Resources Limited, Canadian Natural Albion Sands, Fort Hills Energy Corporation, Imperial Oil Canada Ltd., Suncor Energy Inc., and Syncrude Canada Ltd. 2019. Oil sands bird contact monitoring program. 2018 Annual report. Submitted to the Alberta Energy Regulator. 241 pp.

Catling, P., and G. Mitrow. 2011. The recent spread and potential distribution of Phragmites australis subsp. australis in Canada. Canadian Field-Naturalist 125:95‑104.

CESCC (Canadian Endangered Species Conservation Council). 2020. Wild Species 2020: The General Status of Species in Canada. National General Status Working Group. 128 pp.

Cheskey, E., J. Wells, and S. Casey-Lefkowitz. 2011. Birds at risk: the importance of Canada’s boreal wetlands and waterways. Natural Resources Defense Council, Boreal Songbird Initiative and Nature Canada, Ottawa, Ontario. 32 pp.

Corcoran, R.M., J.R. Lovvorn, and P.J. Heglund. 2009. Long-term change in limnology and invertebrates in Alaskan boreal wetlands. Hydrobiologia 620:77-89.

COSEWIC. 2009. COSEWIC Assessment and Status Report on the Horned Grebe Podiceps auritus, Western Population and Magdalen Islands Population, in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 42 pp.

COSEWIC. 2020. Guidelines for recognizing designatable units. Appendix F5 in COSEWIC Operations and Procedures Manual, revised November 2020. Committee on the Status of Endangered Wildlife in Canada, Environment and Climate Change Canada, Ottawa, Ontario. 7 pp.

Cramp, S., and K.E.L. Simmons. 1977. Handbook of the Birds of Europe, the Middle East, and North Africa: The Birds of the Western Palearctic, Volume 1 (Ostrich to Ducks). Oxford University Press, Oxford, United Kingdom. 722 pp.

Crewe, T., K. Barry, P. Davidson, and D. Lepage. 2012. Coastal waterbird population trends in the Strait of Georgia 1999 – 2011: results from the first 12 years of the British Columbia Coastal Waterbird Survey. British Columbia Birds 22:8-35.

Day, R.H., S.M. Murphy, J.A. Wiens, G.D. Hayward, E.J. Harner, and L.N. Smith. 1997. Effects of the Exxon Valdez oil spill on habitat use by birds in Prince William Sound, Alaska. Ecological Applications 7:593-613.

del Hoyo, J., A. Elliott, and J. Sargatal (eds). 1992. Handbook of the Birds of the World,. 1: Ostrich to Ducks. Lynx Editions, Barcelona, Spain.

Douglas, M., and J.K. Tooker. 2015. Large-scale deployment of seed treatment has driven rapid increase in use of neonicotinoid insecticides and preemptive pest management in US field crops. Environmental Science and Technology 21:5088‑5097.

Douhan, B. 1998. Svarthakedoppingen. En fagel patilbakagang i Sverige (The Horned Grebe. A bird on retreat in Sweden). Vår Fågelvärld 1/1998:7-22.

Dubois, P.J., P. Le Maréchal, G. Olioso, and P. Yésou, P. 2008. Nouvel inventaire des oiseaux de France. Delachaux et Niestlé, Paris, France. 560 pp.

DUC (Ducks Unlimited Canada). 2021. Canadian Wetland Inventory [accessed January 2021].

Eaton, S.W. 1983. Horned Grebes downed by ice storm. American Birds 37:836-837.

Eberhardt, L.E., and A.B. Sargeant. 1977. Mink predation on prairie marshes during the waterfowl breeding season. Pp. 33-43, in R. L. Philips and C. Jonkel (eds). Proceedings of the 1975 Predator Symposium, Missoula, Montana. Montana Forest and Conservation Experiment Station, University of Montana, Missoula, Montana, USA.

ECCC (Environment and Climate Change Canada). 2022. Management Plan for the Horned Grebe (Podiceps auritus), Western population, in Canada. Species at Risk Act Management Plan Series. Environment and Climate Change Canada, Ottawa, Ontario. v + 49 pp.

Environment Canada. 2013. Recovery Strategy for the Horned Grebe (Podiceps auritus), Magdalen Islands Population, in Canada. Species at Risk Act Recovery Strategy Series, Environment Canada, Ottawa, Ontario. iv + 19 pp.

Environment Canada. 2015. Action Plan for the Horned Grebe (Podiceps auritus), Magdalen Islands population, in Canada. Species at Risk Act Action Plan Series, Environment Canada, Ottawa, Ontario. iv + 13 pp.

Ethier, D., P. Davidson, G.H. Sorenson, K.L. Barry, K. Devitt, C.B. Jardine, D. Lepage, and D.W. Bradley. 2020. Twenty years of coastal waterbird trends suggest regional patterns of environmental pressure in British Columbia, Canada. Avian Conservation and Ecology 15(2):20.

Ferguson, R.S. 1977. Adaptations of the Horned Grebe for breeding in prairie pothole marshes. M.Sc. Thesis, University of Manitoba, Winnipeg, Manitoba. 114 pp.

Ferguson, R.S. 1981. Territorial attachment and mate fidelity by Horned Grebes. Wilson Bulletin 93:560-561.

Ferguson, R.S., and S.G. Sealy. 1983. Breeding ecology of the Horned Grebe, Podiceps auritus, in southwestern Manitoba. Canadian Field-Naturalist 97:401-408.

Fink, D., T. Auer, A. Johnston, M. Strimas-Mackey, O. Robinson, S. Ligocki, W. Hochachka, C. Wood, I. Davies, M. Iliff, and L. Seitz. 2020. eBird Status and Trends, Data Version: 2019; Released: 2020. Cornell Lab of Ornithology, Ithaca, New York. Website: https://science.ebird.org/en/status-and-trends/species/horgre/abundance-map?season=breeding.

Fink, D., T. Auer, A. Johnston, M. Strimas-Mackey, S. Ligocki, O. Robinson, W. Hochachka, L. Jaromczyk, A. Rodewald, C. Wood, I. Davies, and A. Spencer. 2022. eBird Status and Trends, Data Version: 2021; Released: 2022. Cornell Lab of Ornithology, Ithaca, New York. Website: https://science.ebird.org/en/status-and-trends/species/horgre/trends-map [accessed 1 February 2023].

Fjeldså, J. 1973a. Distribution and geographical variation of the Horned Grebe Podiceps auritus (Linnaeus, 1758). Ornis Scandinavica 4:55-86.

Fjeldså, J. 1973b. Territory and the regulation of population density and recruitment in the Horned Grebe Podiceps auritus arcticus Boje [sic], 1822. Videnskabelige Meddelelser fra Dansk naturhistorisk Forening 136:117-189.

Fjeldså, J. 1973c. Feeding and habitat selection of the Horned Grebe, Podiceps auritus (Aves), in the breeding season. Videnskabelige Meddelelser fra Dansk naturhistorisk Forening 136:57-95.

Fjeldså, J. 1973d. Antagonistic and heterosexual behaviour of the Horned Grebe, Podiceps auritus. Sterna 12:161-217.

Forsyth, D.J., P.A. Martin, K.D. De Smet, and M.E. Riske. 1994. Organochlorine contaminants and eggshell thinning in grebes from Prairie Canada. Environmental Pollution 85:51-58.

Fournier M.A., and J.E. Hines. 1999. Breeding ecology of the Horned Grebe Podiceps auritus in subarctic wetlands. Occasional Paper No. 99. Canadian Wildlife Service. Environment Canada, Ottawa, Ontario. 32 pp.

Fradette, P. 1992. Les oiseaux des Îles-de-la-Madeleine: populations et sites d’observation. Attention FragÎles, L'Étang-du-Nord, Quebec. 292 pp.

Furness, B., H. Wade, and E.A. Masden. 2013. Assessing the vulnerability of marine bird populations to offshore wind farms. Journal of Environmental Management 119:56-66.

Government of Canada. 2017. Birds protected under the Migratory Birds Convention Act. Website: https://www.Canada.ca/en/environment-climate-change/services/migratory-birds-legal-protection/convention-act.html [accessed December 2020].

Government of Canada. 2019. Breeding Bird Survey results. Website: https://wildlife-species.Canada.ca/breeding-bird-survey-results [accessed December 2020].

Hammell, G. 2017. Changes to the population status of Horned Grebes (Podiceps auritus) and Red-necked Grebes (Podiceps grisegena) in southwestern Manitoba, Canada. Canadian Field-Naturalist 131:317-324.

Hampton, S.T., R.G. Ford, H.R. Carter, C. Abraham, and D. Humple. 2003. Chronic oiling and seabird mortality from the sunken vessel S.S. Jacob Luckenbach in central California. Marine Ornithology 31:35-41.

Harrison, N., and M. Robins. 1992. The threat from nets to seabirds. RSPB Conservation Review 6:51-56.

Hodgson, K.Y. 1979. Operation Horned Grebe. North American Bird Bander 4:110.

Hoar, T. 2007. Horned Grebe. Pp. 144-145 in M.D. Cadman, D.A. Sutherland, G.G. Beck, D. Lepage, and A.R. Couturier (eds.). Atlas of the Breeding Birds of Ontario, 2001-2005, Bird Studies Canada, Environment Canada, Ontario Field Ornithologists, Ontario Ministry of Natural Resources, and Ontario Nature, Toronto, Ontario. xxii + 706 pp.

Howie, R. 2015. Horned Grebe. In P.J.A. Davidson, R.J. Cannings, A.R. Couturier, D. Lepage, and C.M. Di Corrado (eds.). The Atlas of the Breeding Birds of British Columbia, 2008-2012, Bird Studies Canada, Delta, British Columbia. Website: http://www.birdatlas.bc.ca/accounts/speciesaccount.jsp?sp=HOGR&lang=en [accessed December 2020].

Hukee, B.E. 2016. Great Blue Heron (Ardea herodias) captures and kills Horned Grebe (Podiceps auritus). Florida Field Naturalist 44:113-115.

Kagan, R.A., T.C. Viner, P.W. Trail, and E.O. Espinoza. 2014. Avian mortality at solar energy facilities in Southern California: a preliminary analysis. National Fish and Wildlife Forensics Laboratory, Ashland, Oregon. 28 pp.

Kuczynski, E.C., and C.A. Paszkowski. 2012. Constructed borrow-pit wetlands as habitat for aquatic birds in the Peace Parkland, Canada. International Scholarly Research Network Ecology 2012:1-13.

Kuczynski, E.C., C.A. Paszkowski, and B.A. Gingras. 2012. Horned Grebe habitat use of constructed wetlands in Alberta, Canada. Journal of Wildlife Management 76:1694-1702

Larivée, J. 2006. Étude des populations d’oiseaux du Québec (ÉPOQ). Base de données ornithologiques, Association québécoise des groupes d’ornithologues (AQGO), Rimouski, Quebec.

Lewis, H.F. 1924. List of birds recorded from the Island of Anticosti, Quebec. Canadian Field Naturalist 38:43-46.

Lutmerding, J.A., and A.S. Love. 2017. Longevity records of North American birds. Version 2017.1. Patuxent Wildlife Research Center, Bird Banding Laboratory, Laurel, Maryland.

Madsen, F.J. 1957. On the food habits of some fish-eating birds in Denmark: Divers, grebes, mergansers, and auks. Danish Review of Game Biology 3:21-83.

Main, A.R., J.V. Headley, K.M. Peru, N.L. Michel, A.J. Cessna, and C.A. Morrissey. 2014. Widespread use and frequent detection of neonicotinoid insecticides in wetlands of Canada’s Prairie Pothole Region. PloS ONE 9:1-12.

Maloney, E., K. Liber, J.H. Headley, K.M. Peru, and C.A. Morrissey. 2018. Neonicotinoid insecticide mixtures: evaluation of laboratory-based toxicity predictions under semi-controlled field conditions. Environmental Pollution 243:1727‑1739.

Master, L.L., D. Faber-Langendoen, R. Bittman, G.A. Hammerson, B. Heidel, L. Ramsay, K. Snow, A. Teucher, and A. Tomaino. 2012. NatureServe Conservation Status Assessments: Factors for Evaluating Species and Ecosystem Risk. NatureServe, Arlington, Virginia. 64 pp

McKnight, A., K.M. Sullivan, D.B. Irons, S.W. Stephensen, and S. Howlin. Prince William Sound Marine Bird Surveys, Synthesis and Restoration, Exxon Valdez Oil Spill Restoration Project Final Report. U.S. Fish and Wildlife Service, Anchorage, Alaska. 136 pp.

Meehan, T.D., pers. comm. 2022. Email correspondence to M. Gahbauer. August 2022. Lead Analyst, Christmas Bird Count, National Audubon Society.

Meehan, T.D., G.S. LeBaron, K. Dale, K. Krump, N.L. Michel, and C.B. Wilsey. 2020. Abundance trends of birds overwintering in the USA and Canada, from Audubon Christmas Bird Counts, 1966-2019, version 3.0. National Audubon Society, New York, New York.

Mitchell, L. 2018. Horned Grebe. In C. Artuso, A. R. Couturier, K. D. De Smet, R. F. Koes, D. Lepage, J. McCracken, R. D. Mooi, and P. Taylor (eds.). The Atlas of the Breeding Birds of Manitoba, 2010-2014. Bird Studies Canada, Winnipeg, Manitoba. Website: http://www.birdatlas.mb.ca/accounts/speciesaccount.jsp?sp=HOGR&lang=en [accessed December 2020].

MNRF (Ministry of Natural Resources and Forestry). 2018. Horned Grebe Government Response Statement. https://www.Ontario.ca/page/horned-grebe-government-response-statement (Accessed August, 2021)

Morandin, L.A., and P.D. O’Hara. 2016. Offshore oil and gas, and operational sheen occurrence: is there potential harm to marine birds? Environmental Reviews 24:285‑318.

Moritz, C. 1994. Defining ‘Evolutionarily Significant Units’ for conservation. Trends in Ecology and Evolution 9:373-375.

Morrissey, C.A., P. Mineau, J.H. Devries, F. Sanchez-Bayo, M. Liess, M.C. Cavallaro, and K. Liber. 2015. Neonicotinoid contamination of global surface waters and associated risk to aquatic invertebrates: a review. Environment International 74:291‑303.

Natural Resources Canada. 2020. Fire regime. Website: https://www.nrcan.gc.ca/climate-change/impacts-adaptations/climate-change-impacts-forests/forest-change-indicators/fire-regime/17780 [accessed 7 February 2023].

NatureServe. 2020. NatureServe Explorer. NatureServe, Arlington, Virginia. Website: http://explorer.natureserve.org/ [accessed December 2020].

Nero, R.W. 1963. Detergents - a new hazard for water birds. Blue Jay 21:91-93.

Ouellet, H., and R. Ouellet. 1963. Birds notes from Lake Ste-Anne, Saguenay County, Quebec. Canadian Field Naturalist 77:146-153.

Palmer, R.S. (ed.). 1962. Handbook of North American Birds. Volume 1: Loons through Flamingos. Yale University Press, New Haven, Connecticut.

Paulson, D.R. 1969. Commensal feeding in grebes. Auk 86:759.

Pearse, T. 1950. Parasitic birds. Murrelet 31:14.

Pest Management Regulatory Agency. 2017. Re-evaluation Decision RVD2017-01, Glysophate. April 2017.

Peterjohn, B.G. 2001. The Birds of Ohio with Breeding Bird Atlas Maps. Wooster Book Company, Wooster, Ohio. 688 pp.

Piersma, T. 1988. Body size, nutrient reserves and diet of Red-necked and Slavonian Grebes Podiceps grisegena and P. auritus on Lake IJsselmeer, The Netherlands. Bird Study 35:13-24.

Potter, Jr., J.M. 1974. Horned Grebes in mutual display during northward migration. Chat 38:22.

PHJV (Prairie Habitat Joint Venture). 2014. Prairie Habitat Joint-Venture Implementation Plan 2013-2020: The Western Boreal Forest. Report of the Prairie Habitat Joint-Venture. Environment Canada, Edmonton, Alberta.

Richard, A. 2005. Rapport d’inventaire du Grèbe esclavon (Podiceps auritus) à l’étang de l’Est, aux Îles de la Madeleine. Attention FragÎles, Îles-de-la-Madeleine, Quebec. 10 pp.

Rioux, S., J.-P.L. Savard, and A.A. Gerick. 2013. Avian mortalities due to transmission line collisions: a review of current estimates and field methods with an emphasis on applications to the Canadian electric network. Avian Conservation and Ecology 8:7.

Riske, M.E. 1976. Environmental impact upon grebes breeding in Alberta and British Columbia. Doctoral thesis, University of Calgary, Calgary, Alberta. 482 pp.

Robert, M., M.-H. Hachey, D. Lepage, and A.R. Couturier (eds.). 2019. Second Atlas of the Breeding Birds of Southern Québec. Regroupement QuébecOiseaux, Environment and Climate Change Canada, Bird Studies Canada. Montreal, Quebec. 720 pp.

Roland, J.V., G.E. Moore, and M.A. Bellanca. 1977. The Chesapeake Bay oil spill-February 2, 1976: A case history. International Oil Spill Conference Proceedings 1997(1):523-527.

Salafsky, N., D. Salzer, A.J. Stattersfield, C. Hilton-Taylor, R. Neugarten, S.H.M. Butchart, B. Collen, N. Cox, L.L. Master, S. O’Connor, and D. Wilkie. 2008. A standard lexicon for biodiversity conservation: unified classifications of threats and actions. Conservation Biology 22:897-911.

Scheffer, M., S. Carpenter, J.A. Foley, C. Folke, and B. Walker. 2001. Catastrophic shifts in ecosystems. Nature 413:591-596.

Semenchuk, G.P. 2007. Horned Grebe. Pp. 136-137, in The Atlas of Breeding Birds of Alberta: A Second Look. Federation of Alberta Naturalists, Edmonton, Alberta. vii + 626 pp.

Shaffer, F. 2019. Horned Grebe. Pp 162-163, in M. Robert, M-H. Hachey, D. Lepage, and A.R. Couturier (eds.). Second Atlas of the Breeding Birds of Southern Québec, Regroupement QuébecOiseaux, Canadian Wildlife Service (Environment and Climate Change Canada) and Bird Studies Canada. Montreal, Quebec, xxv + 694 pp.

Shaffer, F., pers. comm. 2022. Email correspondence to M. Gahbauer. Biologist, Canadian Wildlife Service, Environment and Climate Change Canada, Quebec City, Quebec.

Shaffer, F., and P. Laporte. 2003. Le Grèbe esclavon (Podiceps auritus) aux Îles-de-la Madeleine: Population, nidification et habitat. Technical Report Series, No. 367, Canadian Wildlife Service, Environmental Conservation Branch, Environment Canada, Sainte-Foy, Quebec. 77 pp.

Sibley, D.A. 1997. Birds of Cape May. Second Edition. Cape May Bird Observatory, New Jersey Audubon Society, Cape May, New Jersey. 168 pp.

Sibley, D.A. 2014. The Sibley Guide to Birds. Second Edition. Scott and Nix Inc., New York, New York. 624 pp.

Sinclair, P., W.A. Nixon, C.D. Eckert, and N.L. Hughes (eds.). 2003. Birds of the Yukon Territory. The University of British Columbia, UBC Press, Vancouver, British Columbia. 595 pp.

Small, A. 1994. California Birds: Their Status and Distribution. Ibis Publishing Company, Vista, California. 342 pp.

Smith, A. 2020. Unpublished data, North American Breeding Bird Survey Canadian Trends. Environment and Climate Change Canada, Ottawa, Ontario.

Smith, J.L., and K.H. Morgan. 2005. An assessment of seabird bycatch in longline and net fisheries in British Columbia. Technical Report Series No. 401. Canadian Wildlife Service, Pacific and Yukon Region.

Soykan, C.U., J. Sauer, J.G. Schuetz, G.S. LeBaron, K. Dale, and G.M. Langham. 2016. Population trends for North American winter birds based on hierarchical models. Ecosphere 7(5).

St. Clair, C.C. 2014. Final Report of the Research on Avian Protection Project (2010 – 2014). Research on Avian Protection Project, Department of Biological Sciences, University of Alberta, Edmonton, Alberta. 95 pp.

Stedman, S.J. 2020. Horned Grebe (Podiceps auritus), version 1.0. In S.M. Billerman (ed.). Birds of the World. Cornell Lab of Ornithology, Ithaca, New York. https://doi.org/10.2173/bow.horgre.01

Steen, V., S.K. Skagen, and B.R. Noon. 2014. Vulnerability of breeding waterbirds to climate change in the Prairie Pothole Region, U.S.A. PLoS ONE 9:1-12.

Stevenson, H.M., and B. H. Anderson. 1994. The Birdlife of Florida. University Press of Florida, Gainesville, Florida. 881 pp.

Storer, R.W. 1969. The behavior of the Horned Grebe in spring. Condor 71:188-205.

Sugden, L.G. 1977. Horned Grebe breeding habitat in Saskatchewan parklands. Canadian Field-Naturalist 91:372-376.

Sugden, L.G., and G.W. Beyersbergen. 1984. Farming intensity on waterfowl breeding grounds in Saskatchewan parklands. Wildlife Society Bulletin 12:22-26.

Taylor, S., pers. comm. 2022. Email correspondence to M. Gahbauer. Weaver Brothers Distinguished Professor, School of Renewable Natural Resources, Louisiana State University, Baton Rouge, Louisiana, and COSEWIC Non-government Science Member.

Timoney, K., and R. Ronconi. 2010. Annual bird mortality in the bitumen tailings ponds in Northeastern Alberta, Canada. The Wilson Journal of Ornithology 122:569-576.

Ulfvens, J. 1988. Comparative breeding ecology of the Horned Grebe Podiceps auritus and the Great Crested Grebe Podiceps cristatus: Archipelago versus lake habitats. Acta Zoologica Fennica 183:1-75.

Ulfvens, J. 1989. Clutch size, productivity and population changes in a population of the Horned Grebe Podiceps auritus in an exposed habitat. Ornis Fennica 66:75-77.

USC (United Stated Code Annotated). 1918. Migratory Bird Treaty Act of 1918. Title 16: Conservation of the United States Code: 703-712. Amended April 16, 2020.

USFWS (United States Fish and Wildlife Service). 2020. Environmental Conservation Online System.

Van Dijk, T.C., M.A. van Staalduinen, and J.P. van der Sluijs. 2013. Macroinvertebrate decline in surface water polluted with imidacloprid. Public Library of Science One 8(5):1-10.

Vermeer, K., W.J. Cretney, J.E. Elliott, R.J. Norstrom, and P.E. Whitehead. 1993. Elevated polychlorinated dibenzodioxin and dibenzofuran concentrations in grebes, ducks, and their prey near Port Alberni, British Columbia, Canada. Marine Pollution Bulletin 26:431-435.

Watmough, M.D, Z. Li, and E.M. Beck. 2017. Prairie Habitat Monitoring Program: Canadian Prairie Wetland and Upland Status and Trend 2001-2011 in the Prairie Joint Venture Delivery Area. Prairie Habitat Joint Venture, Edmonton, Alberta.

Watmough, M.D., and M.J. Schmoll. 2007. Environment Canada’s Prairie and Northern Region Habitat Monitoring Program Phase II: Recent habitat trends in the Prairie Habitat Joint Venture. Technical Report Series No. 493. Environment Canada, Canadian Wildlife Service, Prairie and Northern Region Edmonton, Alberta. xiv + 135 pp.

Wetlands International. 2020. Data-driven Waterbird Population Estimates. Waterbirds Populations Portal. Website: wpe.wetlands.org [accessed December 2020].

Winkler, D.W., S.M. Billerman, and I.J. Lovette. 2020. Grebes (Podicipedidae), version 1.0. In S. M. Billerman, B. K. Keeney, P. G. Rodewald, and T. S. Schulenberg (eds.). Birds of the World, Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.podici1.01

Žydelis, R., J. Bellebaum, H. Ősterblom, M. Vetemaa, B. Schirmeister, A. Stipniece, M. Dagys, M. van Eerden, and S. Garthe. 2009. Bycatch in gillnet fisheries – an overlooked threat to waterbird populations. Biological Conservation 142:1269-1281.

Collections examined

No collections were examined for the preparation of this report.

Authorities contacted

• Abraham, K. Retired Research Scientist. Ontario Ministry of Natural Resources and Forestry and Trent University. Peterborough, Ontario
• Anctil, A. Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs, Quebec
• Bennett, B. Coordinator. Yukon Conservation Data Centre, Ministry of Environment. Whitehorse, Yukon. COSEWIC member
• Benville, A. Data Manager. Saskatchewan Conservation Data Centre. Regina, Saskatchewan
• Breault, A. Wetland Bird Biologist. Canadian Wildlife Service, Environment and Climate Change Canada. Delta, British Columbia
• Brooks, R. Wildlife Research Specialist – Hudson Bay Lowlands. Ontario Ministry of Natural Resources and Forestry. Peterborough, Ontario
• Brown, G. Research Scientist. Ontario Ministry of Natural Resources and Forestry, and Trent University. Peterborough, Ontario
• Burrell, M. Project Zoologist. Ontario Natural Heritage and Information Centre, Ontario Ministry of Natural Resources and Forestry. Peterborough, Ontario. Member of the COSEWIC Birds Specialist Sub-committee
• Campbell, M. Wildlife Biologist. Canadian Wildlife Service, Environment and Climate Change Canada. Whitehorse, Yukon
• Cannings, S. Species at Risk Biologist. Canadian Wildlife Service, Environment and Climate Change Canada. Whitehorse, Yukon. COSEWIC member
• Cooke, H. Associate Conservation Scientist. Wildlife Conservation Society of Canada. Whitehorse, Yukon
• Davy, C. Research Scientist. Ontario Ministry of Natural Resources and Forestry, and Trent University. Peterborough, Ontario
• Gardiner, L. Ecosystem Scientist. Species Conservation, Conservation Programs Branch, Parks Canada. Val Marie, Saskatchewan
• Gauthier, I. Biologiste, Coordonnatrice provinciale des espèces fauniques menacées et vulnérables. Direction générale de la gestion de la faune et des habitats, Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs. Quebec City, Quebec
• Guile, A. Conservation Biologist. Wek’èezhìı Renewable Resources Board. Yellowknife, Northwest Territories
• Jung, T. Senior Wildlife Biologist (Biodiversity). Ministry of Environment. Whitehorse, Yukon. COSEWIC member
• Keith, J. Biodiversity Biologist. Habitat Unit, Ministry of Environment. Regina, Saskatchewan
• Laliberté, B. Wildlife Biologist. Canadian Wildlife Service, Environment and Climate Change Canada. Quebec City, Quebec
• McDonald, R. Senior Environmental Advisor, Department of National Defence. Ottawa, Ontario
• Mehl, K. Manager. Habitat Unit, Fish, Wildlife and Lands Branch, Ministry of Environment, Government of Saskatchewan. Saskatoon, Saskatchewan
• Meijer, M. Data Manager. Alberta Conservation Information Management System. Edmonton, Alberta
• Murray, C. Data Manager. Manitoba Conservation Data Centre. Winnipeg, Manitoba
• Mulder, R. Biodiversity Information Specialist. Ministry of Environment. Whitehorse, Yukon
• Pickett, K. Biologist. Canadian Wildlife Service, Environment and Climate Change Canada. Toronto, Ontario
• Poulin, R. Manager, Research and Collections. Royal Saskatchewan Museum, Museum Annex, Province of Saskatchewan. Regina, Saskatchewan
• Pruss, S. Ecosystem Scientist. Species Conservation, Conservation Programs Branch, Parks Canada. Edmonton, Alberta
• Roy, C. Quantitative Analyst. Migratory Birds and Wildlife Health Section, Environment and Climate Change Canada. Ottawa, Ontario
• Sabine, M. Species at Risk Biologist. Natural Resources and Energy Development. Fredericton, New Brunswick
• Shaffer, F. Biologist. Canadian Wildlife Service, Environment and Climate Change Canada. Quebec, Quebec
• Shepherd, P. Senior Marine Conservation Advisor. Parks Canada. Vancouver, British Columbia. COSEWIC member
• Sinclair, P. Bird Conservation Biologist. Canadian Wildlife Service, Environment and Climate Change Canada. Whitehorse, Yukon
• Smith, A. Senior Biostatistician. Canadian Wildlife Service, Environment and Climate Change Canada. Ottawa, Ontario
• Stipec, K. Client Request Specialist. British Columbia Conservation Data Centre. Delta, British Columbia
• Taylor, S.S. Weaver Brothers Distinguished Professor. School of Renewable Natural Resources, Louisiana State University. Baton Rouge, Louisiana. COSEWIC Non-government Science Member
• Taylor, T. Biodiversity Information Biologist. Ontario Natural Heritage Information Centre. Peterborough, Ontario
• Wilson, J. Bander in Charge, Pointe Lepreau Bird Observatory. Saint John, New Brunswick

Acknowledgements

Funding for the preparation of this report was provided by Environment and Climate Change Canada, with administrative support by Marie-France Noël, Tanya Pulfer, Amit Saini, Joanne Oscanesi and Karen Timm. The authorities listed above provided valuable data and/or advice and their input and expertise is greatly appreciated. The writers would also like to extend their thanks to the staff from the conservation data centres, Natural Heritage Information Centre and the Parks Canada Agency who provided input and data to this report. The contributions by the many volunteers who collected data and completed survey routes for the Breeding Bird Survey, the Christmas Bird Counts, and various atlas projects cannot be overstated, as their efforts are critical to deriving the trends relied on in this report. Special thanks go to Adam Smith and Tim Meehan for their efforts to provide customized three-generation trend estimates, and to COSEWIC Birds Specialist Subcommittee (SSC) Co-chair Marcel Gahbauer, for his invaluable guidance and support in the preparation of this report. SSC members Louise Blight (Co-chair as of 2023), Pete Davidson, Richard Elliot, Andrew Horn and Elsie Krebs provided useful reviews of earlier drafts. Amit Saini and Gerry Schaus created Figures 1 and 2 and completed the EOO calculations. Thanks to Margaret Docker, Sabrina Taylor and Dave Toews for useful conversations and guidance on interpreting the genetic information used to define the Horned Grebe Dus.

Biographical summary of report writer(s)

Kenneth Burrell is a biologist specializing in ornithology. Kenneth has been studying birds for over 20 years and has conducted countless field studies throughout Canada. He is actively involved in the Ontario birding community and publishes widely on topics in field ornithology, ranging from species at risk to the impacts of weather on bird migration, and has recently published a book, Best Places to Bird in Ontario. Kenneth volunteers widely for bird conservation programs, including the CBC, BBS, and various species-at-risk recoveries.

Daniel Riley is a Terrestrial and Wetland Biologist with Natural Resource Solutions Incorporated (NRSI), an environmental consulting firm located in Waterloo, Ontario. As a bird specialist, he leads natural resource inventories and evaluations, environmental impact studies, and research. Daniel is active in the Ontario birding community and is currently serving as secretary of the Ontario Bird Records Committee. Since graduating with a Bachelor of Landscape Architecture from the University of Guelph, Daniel has worked on a number of projects focused on species at risk. These projects include the Windsor-Essex Parkway Project (Butler’s Gartersnake and Eastern Fox Snake) and Birds Canada’s SwiftWatch Program (Chimney Swift).

Nathan Miller is a Terrestrial and Wetland Biologist at NRSI who regularly completes surveys and studies on birds and their habitats at sites across Canada. Nathan has nearly 20 years of experience carrying out migration monitoring, breeding bird point counts and transects, behavioural monitoring, nest searches, and targeted species-at- risk surveys on numerous projects. Nathan is also actively involved in the bird-watching community in Ontario and Canada and regularly contributes data to eBird and other databases.

Appendix 1. Threats calculator results for the Horned Grebe

Threats assessment worksheet

Species or ecosystem scientific name

Horned Grebe Podiceps auritus

Generation time

4 yrs

Date

2021-03-05

Assessor(s)

Adapted from the proposed management plan for the Western subpopulation (ECCC 2022) by Ken Burrell and Marcel Gahbauer

Assigned Overall threat impact:

C = Medium

Classification of Threats adopted from CMP Direct Threats Classification Version 2.0 (Conservation Measures Partnership 2016)