Leach’s Storm-Petrel (Atlantic population) (Oceanodroma leucorhoa): COSEWIC assessment and status report 2020

Official title: COSEWIC assessment and status report on the Leach’s Storm-Petrel (Oceanodroma leucorhoa) Atlantic population in Canada 2020

Threatened 2020

COSEWIC assessment summary

Assessment summary – November 2020

Common name: Leach’s Storm-Petrel - Atlantic population

Scientific name: Oceanodroma leucorhoa

Status: Threatened

Reason for designation:

This small, long-lived pelagic seabird has an extensive global range, nesting on offshore islands in disjunct populations in the North Atlantic and North Pacific Oceans. The Atlantic population nests in underground burrows at more than 80 colonies in eastern Canada. Birds often fly hundreds of kilometres from colonies to forage on tiny bioluminescent fish. This population overwinters in productive equatorial waters of the Atlantic Ocean, with some birds reaching waters off South Africa and Brazil. Surveys at eight major colonies indicate that the number of individuals has declined by 54% over the past three generations (44 years), and the rate of decline is increasing. Some Quebec colonies have been lost in recent years, and expanding Atlantic Puffin colonies are displacing this species from preferred nesting habitat at several large colonies. Low adult survival related to higher predation rates by gulls appears to be a key demographic factor in the observed declines. These declines are expected to continue. Additional threats include changes in the food web of the northwest Atlantic, as well as offshore oil and gas production and attraction to human sources of light which cause collisions and stranding of young birds. Despite declines, the overall population remains large and widespread, with about 5 million mature individuals estimated to breed in Canada.

Occurrence: Quebec, New Brunswick, Prince Edward Island, Nova Scotia, Newfoundland and Labrador, Atlantic Ocean

Status history: Designated Threatened in November 2020.

COSEWIC executive summary

Leach’s Storm-Petrel
Oceanodroma leucorhoa
Atlantic population

Wildlife species description and significance

Leach’s Storm-Petrel is the smallest (∼45 g) and the most wide-ranging procellariiform (petrel) species breeding in the Northern Hemisphere. This tube-nosed seabird is characterized by dark blackish-brown plumage, a forked tail, a broad pale diagonal wing-bar, and a distinctive white rump patch. It breeds in large colonies, nesting in underground burrows that it excavates on coastal and offshore islands.

Canada has considerable global responsibility for Leach’s Storm-Petrel, hosting about 40% of the world’s breeding population. The Atlantic Leach’s Storm-Petrel population in Canada represents about a third of global numbers, with the species’ largest colony at Baccalieu Island, Newfoundland. This species was designated Globally Threatened in 2016 by BirdLife International and uplisted to Vulnerable on the IUCN Red List, based on significant population declines, particularly in the western Atlantic.

Distribution

Leach’s Storm-Petrel breeds mainly in the Northern Hemisphere on offshore islands of the Atlantic (south to ∼41° N) and Pacific (south to ∼25° N) oceans. Atlantic and Pacific populations are considered to be separate designatable units (DUs), as they are geographically disjunct with very limited opportunities for gene exchange, and only the Atlantic DU is considered here.

There are up to 93 active Atlantic Leach’s Storm-Petrel breeding colonies in eastern Canada, from southern Labrador to the mouth of the Bay of Fundy in New Brunswick, including the Gulf of St. Lawrence in Quebec. The species breeds most abundantly along Newfoundland’s east and south coasts and Nova Scotia’s Atlantic coast. Atlantic Leach’s Storm-Petrel over-winters primarily between equatorial Atlantic waters and the southwest coast of Africa, as well as in the western Atlantic Ocean off Brazil.

Habitat

Leach’s Storm-Petrel breeds on vegetated islands generally free of mammalian predators, and prefers well-drained habitats suitable for excavating underground burrows, such as low forest and meadow. Atlantic Leach’s Storm-Petrel usually nests on islands occupied by other seabirds, often including large gulls, and tends to use different habitat from other burrow-nesting species. The quantity and quality of suitable habitat has decreased at some colonies, primarily as a result of encroachment by species such as Atlantic Puffin.

Atlantic Leach’s Storm-Petrel is a surface-feeder, foraging over or beyond the continental shelf during the breeding season. It travels 400-800 km from colonies to forage nocturnally in open oceanic waters on vertically migrating bioluminescent lantern-fish, among other prey. During the non-breeding period, Atlantic Leach’s Storm-Petrel is primarily associated with warm productive waters, in areas with high nutrient upwelling or in coastal regions.

Biology

Atlantic Leach’s Storm-Petrel typically first breeds at 6-7 years of age in Canada, with a generation time estimated at 14.8 years under normal conditions. However, in eastern Canada, effective generation time is likely to be lower, as adult survival is estimated at only ∼0.78-0.86 across several colonies in Atlantic Canada. Adults are monogamous and show high nest site fidelity, generally returning to the same nesting burrow each year to raise a single chick. In contrast, young birds rarely return to their natal colony to breed, suggesting that Leach’s Storm-Petrel colonies across the Atlantic Ocean act as one metapopulation as a result of high natal dispersal. Incubation takes 37-50 days, and chicks fledge at 58-77 days of age. Atlantic Leach’s Storm-Petrel is strictly nocturnal at the colony, where all adult arrivals, departures, and chick fledging take place at night.

Population size and trends

A total of 106 colonies either currently or previously supported breeding Leach’s Storm-Petrels in eastern Canada, with the current population estimated at about 5,277,000 mature individuals. Twenty islands that each support colonies with over 2,000 mature individuals collectively host 99.7% of the population. Ten colony sites which previously hosted breeding storm-petrels are known to have been abandoned within the past three generations, resulting in an estimated decline in the index of area of occupancy of about 11% over that period.

Trend analyses were conducted for eight colonies that account for about 91% of the eastern Canadian population, and include all major colonies. An average annual rate of decline of -1.74%/year was observed at monitored colonies over the past three generations (44 years), with a steeper decline of -2.64%/year observed over the past two generations (30 years). Estimated reductions are similar over these two time periods because the rate of decline steepened in recent years, with a -55.2% decline over the past two generations, and -53.8% over the past three generations. Paleo-ecological studies at Baccalieu Island show a peak population size in the mid-1980s followed by a rapid decline, corroborating population trends estimated using traditional surveys. Populations of Leach’s Storm-Petrel at a colony in Saint-Pierre et Miquelon, France, adjacent to Newfoundland, appear to be generally stable, and the much smaller Maine population in the United States is increasing. However, all potential source colonies in the eastern Atlantic are declining.

Threats and limiting factors

Factors driving the decline of Atlantic Leach’s Storm-Petrel population are currently unknown, but are likely multi-factorial. Low annual adult survival rates at colonies across eastern Canada appear to be a key demographic factor contributing to observed declines, and are partly influenced by high predation by large gulls at some breeding colonies. Poor annual survival for Atlantic Leach’s Storm-Petrel contrasts with estimates of ∼0.97 for populations along Canada’s Pacific coast. Atlantic Leach’s Storm-Petrel is threatened by offshore oil and gas production and other marine industries, primarily through light attraction causing collisions and strandings on offshore structures and vessels. Artificial lights in communities or industrial sites near colonies cause recently fledged Leach’s Storm-Petrels to collide with structures or become stranded on the ground, where they are vulnerable to predation. Expanding Atlantic Puffin colonies are encroaching onto nesting habitat at the largest storm-petrel colonies. Rising global temperatures appear to be causing reduced breeding success in some colonies at the southern edge of the range. The incidence of severe weather events associated with climate change is increasing, contributing to mass strandings of Leach’s Storm-Petrels, and ecosystem changes associated with abnormally high temperatures may affect prey availability on their breeding and wintering grounds. Exposure to high levels of mercury, as well as other contaminants acquired through the ingestion of plastic particles, may have negative effects on adult survival, reproductive success, and recruitment.

Protection, status and ranks

Leach’s Storm-Petrel is protected in Canada under the federal Migratory Birds Convention Act, 1994 and parallel legislation in the United States and Mexico. Currently in Canada, 29 islands, which together host 93% of the Atlantic Leach’s Storm-Petrel population, are protected federally as Migratory Bird Sanctuaries or National Parks, or provincially as Wildlife Management Areas or Seabird Ecological Reserves.

Technical summary

Scientific name: Oceanodroma leucorhoa

English name: Leach’s Storm-Petrel (Atlantic population)

French name: Océanite cul-blanc (population de l’Atlantique)

Range of occurrence in Canada: Quebec, New Brunswick, Prince Edward Island, Nova Scotia, Newfoundland and Labrador, Atlantic Ocean

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]?

Threats:

A threats calculator was completed on 13 January 2020 by: Sabina Wilhelm, April Hedd, Greg Robertson, Ingrid Pollet (report writers), Richard Elliot (SSC Co-chair), David Fraser (facilitator), Marie-France Noël (COSEWIC secretariat), Courtney Baldo, Louise Blight, Neil Burgess, Josh Cunningham, Dave Fifield, Marcel Gahbauer, Carina Gjerdrum, Rielle Hoeg, Andy Horn, Jessica Humber, Elsie Krebs, Bob Mauck, Mark McGarrigle, Pam Mills, Bill Montevecchi, Allison Moody, Jean-François Rail, Michael Rodway, Rob Ronconi, Donald Sam, Dave Shutler, Iain Stenhouse, Laura Tranquilla

The assigned overall threat impact is High-High, and the following contributing threats were identified, listed in decreasing order of impact:

3.1 Oil and gas drilling (Medium)
8.2. Problematic native species (Medium)
9.6 Excess energy (Medium-low)
11.1 Habitat shifting and alteration (Medium-low)
8.1 Invasive non-alien/native species (Low)
9.2. Industrial and military effluents (Low)
9.4 Garbage and solid waste (Low)
11.4 Storms and flooding (Low)
7.3 Other ecosystem modifications (Negligible)
6.1. Recreational activities (Negligible)
6.3. Work and other activities (Negligible)
3.3. Renewable Energy (Unknown)
9.5. Air-borne pollutants (Unknown)

What additional limiting factors are relevant?

As Atlantic Leach’s Storm-Petrel has low reproductive potential (first breeding at 6-7 years and raising a maximum of one chick/year), consistently low annual adult survival rates currently observed at many colonies contribute to population declines, and severely limit their ability to recover. High fidelity to specific breeding colonies exhibited by breeding-age adults may limit colony growth, by preventing adults from moving to other colonies if local conditions contribute to low adult survival. High natal dispersal rates exhibited by juvenile Atlantic Leach’s Storm-Petrels may be a limiting factor if emigration of young birds from Canadian colonies exceeds immigration from colonies in other countries in the North Atlantic.

Data sensitive species

Is this a data sensitive species? No

Current status

COSEWIC status history: Designated Threatened in November 2020.

Status and reasons for designation:

Status: Threatened

Alpha-numeric codes: Meets criteria for Endangered, A2bce+4bce, but designated Threatened, A2bce+4bce, as the population remains widespread and abundant, and is thus not facing imminent extirpation.

Reasons for designation: This small, long-lived pelagic seabird has an extensive global range, nesting on offshore islands in disjunct populations in the North Atlantic and North Pacific Oceans. The Atlantic population nests in underground burrows at more than 80 colonies in eastern Canada. Birds often fly hundreds of kilometres from colonies to forage on tiny bioluminescent fish. This population overwinters in productive equatorial waters of the Atlantic Ocean, with some birds reaching waters off South Africa and Brazil. Surveys at eight major colonies indicate that the number of individuals has declined by 54% over the past three generations (44 years), and the rate of decline is increasing. Some Quebec colonies have been lost in recent years, and expanding Atlantic Puffin colonies are displacing this species from preferred nesting habitat at several large colonies. Low adult survival related to higher predation rates by gulls appears to be a key demographic factor in the observed declines. These declines are expected to continue. Additional threats include changes in the food web of the northwest Atlantic, as well as offshore oil and gas production and attraction to human sources of light which cause collisions and stranding of young birds. Despite declines, the overall population remains large and widespread, with about 5 million mature individuals estimated to breed in Canada.

Applicability of criteria

Criterion A (Decline in Total Number of Mature Individuals): Meets Endangered A2bce and A4bce. Observed 54% decline in number of mature individuals over the past three generations (44 years), based on trends from breeding colony surveys, is higher than threshold level. This decline is based in part on declines in the index of area of occupancy and the extent and quality of habitat, and on effects of competition for nesting habitat, gull predation and light pollution. These declines and effects are likely to continue into the future, based on assessed high overall threat impact, with a likely population decline >50% over a three-generation period spanning past and future.

Criterion B (Small Distribution Range and Decline or Fluctuation): Not applicable, as EOO of 850,992 km² is higher than thresholds, and IAO of 284 km² is lower than the threshold for Endangered, but population is not severely fragmented, occurs at more than 10 locations, and does not experience extreme fluctuations.

Criterion C (Small and Declining Number of Mature Individuals): Not applicable, as population estimate of 5,277,000 mature individuals is higher than thresholds.

Criterion D (Very Small or Restricted Population): Not applicable, as population estimate of 5,277,000 mature individuals is higher than thresholds, and index of area of occupancy exceeds 20 km².

Criterion E (Quantitative Analysis): Not applicable, as analysis not conducted.

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

(2020)

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)*

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)**

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

Data Deficient (DD)***

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.

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.

** Formerly described as “Not In Any Category”, or “No Designation Required.”

*** 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.

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

Scientific name: Oceanodroma leucorhoa

English name: Leach’s Storm-Petrel (Atlantic population)

French name: Océanite cul-blanc (population de l’Atlantique)

Classification: Class: Aves

Order: Procellariiformes

Family: Hydrobatidae

Vernacular synonym names in Newfoundland include Mother Carey’s Chicken, Mother Carey’s Chick, Pall Carey, Carey’s Chicken, Carey’s Chick, Carey, and Mother Careys (Montevecchi and Wells 1987).

The scientific name Oceanodroma leucorhoa (Vieillot 1818) is synonymous with Hydrobates leucorhous, the latter proposed in the Handbook of the Birds of the World (Carboneras et al. 2019) and by BirdLife International (BirdLife International 2018), and subsequently adopted by many international bodies.

Morphological description

Leach’s Storm-Petrel is a small (∼45 g) tube-nosed-seabird with dark blackish-brown plumage, long wings angled at the carpal joint, and a forked tail (cover page photo). It has a broad pale diagonal wing-bar formed by the greater secondary coverts, and throughout much of its range, including Canada, it has a distinctive white rump patch (Pollet et al. 2019a). Juveniles resemble adults upon fledging, but with dark grey as opposed to blackish-brown plumage. Breeding and basic (winter) plumages are similar, except that the dark feathers become gradually browner with wear for all age classes. The species is sexually monomorphic (Pollet et al. 2019a).

Population spatial structure and variability

Leach’s Storm-Petrel breeds on offshore islands in the North Atlantic and North Pacific Oceans, in colonies that range in size from tens to millions of breeding pairs. Although the taxonomy of Leach’s Storm-Petrel has been somewhat controversial and confused (Pollet et al. 2019a), two subspecies are currently recognized; O. l. leucorhoa and O. l. chapmani. The latter subspecies breeds only on islands off the Baja California peninsula of Mexico, and only O. l. leucorhoa occurs in Canada.

About 500,000 pairs (1 million mature individuals) from the Pacific population breed in colonies widely scattered along the British Columbia coast (Hipfner 2015). Leach’s Storm-Petrel populations breeding along Canada’s Atlantic and Pacific coasts are genetically distinct. Bicknell et al. (2012) and Taylor et al. (2018) studied the population genetic structure of O. l. leucorhoa throughout the North Atlantic and part of the North Pacific range using mitochondrial DNA and microsatellite markers. Both studies revealed significant differentiation between populations breeding in the Atlantic and the North Pacific Oceans.

Population genetics studies suggest that Leach’s Storm-Petrel breeding throughout the Atlantic Ocean area act as a single metapopulation (Bicknell et al. 2012). The genetic structure is homogeneous across colonies within the Atlantic Ocean (Bicknell et al. 2012), driven by high rates of dispersal, as most immature birds emigrate from their natal colonies and recruit into other colonies across the Atlantic Ocean (Bicknell et al. 2013), although adults of breeding age are not known to move among colonies.

Designatable units

There is compelling evidence for considering the Leach’s Storm-Petrel populations breeding on the Atlantic and Pacific coasts of Canada as discrete and evolutionarily significant, and thus as two separate designatable units (DUs) for the purpose of status assessment. As detailed above (see Population Spatial Structure and Variability) genetic analyses indicate that these populations are genetically distinct (Bicknell et al. 2012; Taylor et al. 2018). They are also geographically disjunct and occur in different Canadian ecozones. Furthermore, there is no overlap between their over-wintering grounds; birds from Atlantic colonies over-winter from equatorial to temperate waters in the South Atlantic Ocean, while birds from Pacific colonies over-winter in the Eastern Tropical Pacific Ocean (Pollet et al. 2014; Halpin et al. 2018; Pollet et al. 2019b; Hedd unpubl. data.). Population sizes and trends are relatively well-known for the Atlantic population and poorly known for the Pacific. Because they occur in different ocean basins, natural and anthropogenic factors influencing population size and trends are likely to differ. Although Bicknell et al. (2012) provide evidence of very limited gene exchange between the oceans, the highly philopatric nature of adults following recruitment (Pollet et al. 2019a), and limited opportunity for Atlantic and Pacific breeders to mix during the non-breeding season, suggests that this flow would be unlikely to limit local adaptations.

Leach’s Storm-Petrel (Atlantic population), or Atlantic Leach’s Storm-Petrel, refers here to the DU which includes birds breeding in eastern Canada, in the provinces of Newfoundland and Labrador, New Brunswick, Nova Scotia, and Quebec, and its status is assessed in this report. The population breeding on the Pacific coast of British Columbia is considered in this report to be a separate DU, referred to as Leach’s Storm-Petrel (Pacific population) or Pacific Leach’s Storm-Petrel, and its status is not assessed here.

Special significance

Leach’s Storm-Petrel is the smallest and the most wide-ranging procellariiform species breeding in the Northern Hemisphere (Pollet et al. 2019a), with a global population estimated to number over 16 million individuals (Pollet et al. 2019a). Canada has considerable global responsibility for the species, hosting close to 40% of the world’s breeding population. The Atlantic Leach’s Storm-Petrel population in Canada represents about a third of the global breeding population, with the species’ largest colony at Baccalieu Island, Newfoundland and Labrador (Sklepkovych and Montevecchi 1989; Pollet et al. 2019a; Wilhelm et al. 2020). Aboriginal Traditional Knowledge was not available for Atlantic Leach’s Storm-Petrel. However, the species is part of coastal and marine ecosystems that are important to Indigenous people, who recognize the interconnectedness of all species within the ecosystem.

Distribution

Global range

Leach’s Storm-Petrel has an extensive global range, with breeding confined mainly to the Northern Hemisphere on offshore islands of the Atlantic and Pacific Oceans (Figure 1). In the North Atlantic, major breeding centres occur in Canada and the adjacent French territory of Saint-Pierre et Miquelon, with smaller populations in the northeastern United States, Scotland, Iceland, Norway, the Faroe Islands (Denmark) and Ireland (Tables 1, 2). Very small numbers also breed on islands off South Africa (Underhill et al. 2002). Birds spend the nonbreeding season (November to April) exclusively at sea, where they are widely distributed. In the Atlantic, many winter in tropical regions, particularly off West Africa and Brazil (Pollet et al. 2014, 2019a; Hedd unpubl. data).

Figure 1. Global distribution of Leach’s Storm-Petrel Oceanodroma leucorhoa. From BirdLife International (2019).

Atlantic Leach’s Storm-Petrel Canadian range

The Atlantic Leach’s Storm-Petrel population breeds at 93 sites along the east coast of Canada (Tables 1 and 2), from southern Labrador to the mouth of the Bay of Fundy (Figure 2), including the Gulf of St. Lawrence and islands along Quebec’s North Shore (Lormée et al. 2012; Wilhelm 2017; Rail unpubl. data). Eleven sites in Atlantic Canada host significant numbers (i.e., > 20,000 mature individuals), with birds breeding most abundantly along Newfoundland’s east and northeast coasts and Burin Peninsula, and Nova Scotia’s Atlantic coast (Figure 2). Smaller colonies are found in the Grand Manan Archipelago in the Bay of Fundy (New Brunswick), the Gulf of St. Lawrence (Quebec’s North Shore, Gaspé Peninsula, and Magdalen Islands), and Newfoundland’s Northern Peninsula and south coast. It is important to note that Grand Colombier, a seabird colony hosting a significant Atlantic Leach’s Storm-Petrel colony (∼ 400,000 mature individuals), is located 20 km off the coast of the Burin Peninsula of Newfoundland, but within the French territory of Saint-Pierre et Miquelon (Lormée et al. 2012; Duda et al. 2020a; Figure 2).

Figure 2. Distribution and relative size of Atlantic Leach’s Storm-Petrel breeding colonies in eastern Canada (orange circles), and Saint-Pierre et Miquelon, France (red circle). Map prepared by S. Wilhelm based on information in Appendix 1.

Atlantic Leach’s Storm-Petrels breeding in Newfoundland colonies forage over and beyond the continental shelf, from the Laurentian Fan onto the Grand Banks, Flemish Cap, and Orphan Basin, and beyond the shelf into the Newfoundland Basin as far north as the western Labrador Sea (Hedd et al. 2018; Figure 3). Storm-petrels breeding in Nova Scotia colonies also forage primarily in deep waters, off the Scotian Shelf and southwest of the Grand Bank (Hedd et al. 2018; Figure 3). In contrast, Leach’s Storm-Petrels breeding in the Bay of Fundy, New Brunswick, forage in shallower waters within the Gulf of Maine and George’s Bank (Hedd et al. 2018; Figure 3). Leach’s Storm-Petrel does not breed on Prince Edward Island (Elliot 2015), although small numbers occur uncommonly but regularly several km off the northeastern and eastern shores of the province in late summer and early autumn (McAskill et al. 2014).

Figure 3. Tracks of foraging trips during the incubation period by 131 Atlantic Leach’s Storm-Petrels from seven eastern Canadian breeding colonies, 2013-2014 (Hedd et al. 2018).

Tracking of Atlantic Leach’s Storm-Petrels from five Canadian colonies indicates that birds range widely during the non-breeding season, wintering in the eastern Atlantic basin between the tropics and southern Africa and in the western Atlantic basin off the coast of Brazil (Pollet et al. 2014, 2019b; Hedd unpubl. data; Figure 4). About one third of Atlantic Leach’s Storm-Petrels outfitted with geolocation devices in Canadian breeding colonies wintered off the southwest coast of Africa, with the remainder off South America (Pollet et al. 2019b; Hedd unpubl. data).

Figure 4. Non-breeding distribution of thirteen Atlantic Leach’s Storm-Petrels tracked using GLS tags from Bon Portage Island and Country Island, Nova Scotia in (A) 2012-13 and 2013-14, and (B) 2014-15 and 2015-16 (Pollet et al. 2019b). Winter (December-February) distribution of twenty-two Atlantic Leach’s Storm-Petrels tracked from (C) Gull Island (2012-13 and 2014-15), and (D) Baccalieu Island (2013-14 to 2017-18; Hedd unpubl. data), Newfoundland. Different colours in all panels represent records of different individuals.

Extent of occurrence and area of occupancy

The extent of occurrence (EOO) for Atlantic Leach’s Storm-Petrel is estimated as 850,992 km², calculated as a minimum convex polygon around all Canadian colonies with confirmed breeding records since 1970 (Figure 5).

Figure 5. Map showing recent colonies with confirmed breeding records since 1970 (black dots) and historical breeding colonies (no confirmation since 1970; open dots) for Atlantic Leach’s Storm-Petrel in Eastern Canada. Extent of occurrence (EOO) is shown within the orange polygon, and index of area of occupancy (IAO) is shown in red within black dots showing recent colony sites. Map prepared by S. Allen, COSEWIC Secretariat, based on information in Appendix 1.

The index of area of occupancy (IAO) is 284 km², calculated using the number of 2 x 2 km grid cells which include the coordinates of recent Atlantic Leach’s Storm-Petrel colonies that have confirmed breeding records since 1970 (Figure 5).

The IAO has declined over the past three generations, as a result of the abandonment of ten colony sites within the current range that previously held small numbers of breeding storm-petrels, but where none were present when last visited (Figure 5, Appendix 1). The corresponding decline in IAO is estimated to be about 11% over three generations. As all colony visits that detected abandoned sites were conducted in 1990 or later (Appendix 1), this decline was actually detected within the past two generations. Note that this estimate is approximate, as some recent colonies may not have been active in 1970, and some others that have not been recently checked may also no longer be occupied.

Search effort

The distribution and abundance of breeding Atlantic Leach’s Storm-Petrels must be determined through ground surveys, because storm-petrels are not observed at colonies during the day due to their nocturnal habits during the breeding season. Systematic monitoring of important seabird colonies, initiated across eastern Canada in the 1970s and 1980s, was key to identifying the positions of major Leach’s Storm-Petrel colonies, and providing robust population estimates (Nettleship 1980; Cannell and Maddox 1983; Cairns et al. 1989; Erskine 1992). Efforts have been made since 2001 to update population estimates at significant storm-petrel colonies across the region (Robertson et al. 2006; Wilhelm et al. 2015, 2017, 2020; Pollet and Shutler 2018; d’Entremont et al. 2020). Previously unreported colonies have been identified during surveys for other breeding seabirds in Nova Scotia and New Brunswick (Ronconi and Wong 2003; Wilhelm 2017). Furthermore, acoustic recording devices were installed on islands along Quebec’s North Shore and in Nova Scotia to detect Leach’s Storm-Petrel where colonies were previously known to be active, and to identify new colonies (Rail pers. comm. 2019; d’Entremont pers. comm. 2020). Combined, these approaches provide a comprehensive understanding of the current distribution and abundance of Atlantic Leach’s Storm-Petrel.

Terrestrial habitat

Terrestrial habitat requirements

Leach’s Storm-Petrel nests on forested or otherwise vegetated islands in underground burrows that they excavate, or less frequently in natural crevices (Pollet et al. 2019a). Soil characteristics of different habitat types may influence the quality of habitat, and Leach’s Storm-Petrel burrow density is positively correlated with soil depth, with deeper soil typically found in forest, grass, and meadow habitats (Grimmer 1980; Stenhouse and Montevecchi 2000), compared to heath (Sklepkovych and Montevecchi 1989). The compressibility of the soil, as well as its moisture content, further affects its quality, with Leach’s Storm-Petrel showing a preference for excavating burrows in soil that is loose (Mackinnon 1988; Stenhouse and Montevecchi 2000) and dry (Fricke et al. 2015).

Changes in vegetation, sometimes associated with removal of invasive herbivores (d’Entremont et al. 2020), may result in changes of storm-petrel habitat use over time.

Habitat quality is also influenced by the presence of avian predators. For example, on islands where gulls (Larus spp.) are present and nesting in open habitats, Leach’s Storm-Petrel predominantly nests in forested habitat (Mackinnon 1988; Stenhouse et al. 2000; Wilhelm et al. 2015); in the absence of large gull colonies, Leach’s Storm-Petrel breeds in higher densities in open fern and grass habitats than in forested habitat (Wilhelm et al. 2020). Large-scale population declines of breeding Herring (Larus argentatus) and Great Black-backed Gulls (L. marinus) have occurred across eastern Canada since the reduction of groundfish fishing activities in the 1990s, and due to improvement of waste management practices, which had artificially increased gull numbers by providing anthropogenic food sources (Regular et al. 2013; Wilhelm et al. 2016). As a result of their large numbers, gulls had caused habitat alteration at Leach’s Storm-Petrel colonies on both Gull and Great Islands, Newfoundland, in particular of meadow habitat occupied by storm-petrels (Bond et al. 2016). However, Herring Gulls have recently initiated or re-established a colony on Baccalieu Island, Newfoundland, following extirpation of resident Red Fox (Montevecchi pers. comm. 2020) which had likely deterred gulls from nesting there (Sklepkovych and Montevecchi 1989; Wilhelm et al. 2020).

Terrestrial habitat trends

Suitable breeding habitat is limited to offshore islands, and although terrestrial habitat trends are generally stable overall, some notable changes have occurred. For example, Atlantic Puffins (Fratercula arctica) are excavating nest burrows in grassy habitat used by nesting Leach’s Storm-Petrels at the three largest colonies in Newfoundland, thereby displacing storm-petrels and/or reducing the quantity of preferred habitat (Wilhelm et al. 2015, 2020; Wilhelm unpubl. data). The proportions of habitat have changed on Baccalieu Island for unknown reasons, with a decline in forested habitat of 70.6 ha (25%) from 1984-2013 (Wilhelm et al. 2019). However, fern habitat, which supports the highest density of Leach’s Storm-Petrel on Baccalieu, increased from 15.4 ha to 53.9 ha over the same period, and currently hosts over half the storm-petrel numbers on the island (> 2 million mature individuals; Wilhelm et al. 2020).

The spread of sphagnum moss (Sphagnum spp.) on Bon Portage Island, Nova Scotia, from 2001 to 2017 has reduced the quantity and quality of potential breeding habitat by creating moist ground unsuitable for Leach’s Storm-Petrel nesting (Pollet and Shutler 2018). The quality of suitable terrestrial habitat there is further compromised by the presence of introduced White-tailed Deer (Odocoileus virginianus) and Snowshoe Hare (Lepus americanus), whose browsing prevents forest regeneration (Pollet pers. obs.; Shutler pers. comm. 2019). Snowshoe Hare had previously caused similar habitat degradation on Kent Island, New Brunswick, but these animals were eradicated by 2007 (Wheelwright 2016; d’Entremont et al. 2020).

Marine habitat

Marine habitat requirements

Atlantic Leach’s Storm-Petrel forages over the continental shelf during the breeding season, moving into open oceanic waters to feed on abundant small fish, primarily mesopelagic lantern-fish (family Myctophidae), and crustacea (Hedd and Montevecchi 2006; Hedd et al. 2009, 2018; see Diet and Foraging Behaviour below). As a consequence, habitat characteristics associated with foraging areas vary in depth (average 900-4000 m), sea surface temperature (10.6-23.3⁰C), and chlorophyll-a concentration (0.2-0.9 mg/m³) across their eastern Canadian summer foraging range (Hedd et al. 2018).

In winter, the probability of occurrence of Leach’s Storm-Petrel is positively associated with high sea surface temperatures and high chlorophyll-a concentrations (Pollet et al. 2019b), in productive upwelling regions and highly eutrophic coastal regions. The latter Net Primary Production areas (Boyd et al. 2014; see Marine Habitat Trends below), include fronts and eddies where upwelling brings prey to the surface (Pollet et al. 2019a; see Diet and Foraging Behaviour below). Net Primary Production refers to the storage of energy produced by plants through photosynthesis and available to be consumed by zooplankton, which forms the basis of marine ecosystem food chains (Boyd et al. 2014). Plankton is a rich food source for small fish and copepods, which in turn form the basis of the Leach’s Storm-Petrel diet (Hedd et al. 2009; see Diet and Foraging Behaviour below).

Marine habitat trends

Although changes in marine habitat of Leach’s Storm-Petrel are currently not well understood, increasing anthropogenic activities in the vicinity of breeding colonies and the marine environment are degrading the quality of the marine habitat of Leach’s Storm-Petrel.

Light pollution represents a threat to Leach’s Storm-Petrel because of its nocturnal nature and vulnerability to light attraction, and is one of the most rapidly growing human-related pressures affecting the natural landscape globally (Cinzano et al. 2001). As a consequence, the quality of marine habitat of Leach’s Storm-Petrel is decreasing along coastlines near important colonies in Newfoundland (Baccalieu, Gull and Great Islands) and Nova Scotia (Country Island), as a result of industrial and residential development (Wilhelm et al. 2013; Wilhelm unpubl. data). Leach’s Storm-Petrel’s offshore marine habitats are also experiencing ongoing degradation, due to increased oil and gas exploration and production in Canada and internationally. The quality of both breeding and wintering grounds is deteriorating with increased light and oil pollution, from sources that include flaring, vessel traffic, chronic operational discharges of hydrocarbons, and accidental oil spills (Fraser et al. 2006; Montevecchi 2006; Ellis et al. 2013; Ronconi et al. 2015; Falchi et al. 2016; see Threats Category 3.1: Oil and Gas Drilling below).

The production of plastic-generated waste is increasing globally (Jambeck et al. 2015), with plastics degrading the marine habitat of all seabirds, including Leach’s Storm-Petrel (O’Hanlon et al. 2017). Plastic pollution in the marine environment poses direct risks to Leach’s Storm-Petrel, as adults are prone to ingesting small particles which can then be offloaded to their offspring (Bond and Lavers 2013; Krug 2020; Krug et al. 2020; see Threats Category 9.4: Garbage and Solid Waste ).

Long-term trends predict that with climate change, Net Primary Production will decrease in the lower latitudes (i.e., the tropics) but will increase in the high latitudes (i.e., the Arctic; Boyd et al. 2014). Such trends would likely decrease the quality of Leach’s Storm-Petrel winter marine habitat, which in turn could affect juvenile and adult survival on their wintering grounds (see Threats Category 11.1: Habitat Shifting and Alteration).

Biology

Atlantic Leach’s Storm-Petrel has been the subject of continuous studies since 1955 on Kent Island (New Brunswick) and shorter studies on Machias Seal Island (New Brunswick); Baccalieu, Great and Gull Islands (Newfoundland); and Bon Portage and Country Islands (Nova Scotia). This section draws mainly on information from those islands, supplemented with additional information from the Birds of North America species account (Pollet et al. 2019a).

Life cycle and reproduction

A typical procellariform, Leach’s Storm-Petrel is a long-lived species, with the oldest known breeding individual aged at least 36 years (Pollet et al. 2019a; Bird et al. 2020). BirdLife International recently estimated generation time to be 14.81 years for this species under normal conditions (Bird et al. 2020). Whereas high annual adult survival is considered necessary to maintain stable populations of long-lived seabirds, recent studies (2003-2018) suggest that annual adult survival of Atlantic Leach’s Storm-Petrel is low across much of the eastern Canadian breeding range (Fife et al. 2015; Pollet et al. 2019a; Fraser and Russell unpubl. data; Hedd unpubl. data). Apparent survival was estimated at 0.78 ± 0.04 at Bon Portage Island, Nova Scotia from 2009 to 2014 (Fife et al. 2015), and unpublished estimates for three Newfoundland colonies, including Baccalieu (2013-2018), Gull (2003-2017; Hedd unpubl. data), and Middle Lawn (2003-2008; Fraser and Russell unpubl. data) Islands are in the range of ∼0.79-0.86. Previous estimates for Kent Island, New Brunswick, indicated that while adult survival generally increased between breeding years 1-2, 2-3, and 3+, yearly-averaged annual survival from 1962 to 1995 for birds in their third breeding year and beyond was 0.87 ± 0.03 (Mauck et al. 2012).

Significantly, apparent annual survival, estimated using the same field techniques and within the same time period, was substantially higher for adult Pacific Leach’s Storm-Petrel breeding at two sites on the coast of British Columbia, at 0.975 ±0.01 (2006-2010; Rennie et al. 2020). Survival rates in Atlantic Canada are generally below reports for Leach’s Storm-Petrel globally (average of about 0.84; Bird et al. 2020), other storm-petrels, and most related tube-nosed seabirds (generally > 0.90; reviewed by Fife et al. 2015). High adult mortality may be due to a combination of factors (see Threats below).

The age of first breeding has been reported as early as 3 years, but most commonly occurs at age 5 or older, with the mean age of first breeding estimated at 6-7 years (Pollet et al. 2019a). Individuals may prospect empty burrows or dig new ones at least one season before actually breeding (Pollet et al. 2019a).

Atlantic Leach’s Storm-Petrel typically returns to the colony in April or May (Pollet et al. 2019a). It is strictly nocturnal around the breeding colony, with individuals flying to and from their burrows only at night (Pollet et al. 2019a). Individual birds show high site fidelity, with pairs reuniting annually at their burrow (Pollet et al. 2019a). If an individual does move to a new burrow, it is typically within 20 m of the previous nest site (Morse and Buchheister 1979). Egg-laying occurs between the end of May and the end of July, with the incubation period ranging from 37 to 50 days (Pollet et al. 2019a). Females lay one egg/season, but may relay if the first egg is lost early in the breeding season (Bond and Hobson 2015). Leach’s Storm-Petrel is monogamous, with no evidence of extra-pair fertilization (Mauck et al. 1995). Eggs hatch between early July and late September. Chicks are left unattended after being brooded for the first 1-5 days, and the adults only visit the burrow at night to feed their young (Pollet et al. 2019a).

Atlantic Leach’s Storm-Petrels show variability in breeding success across their breeding range. Hatching success (proportion of eggs laid that hatched) tends to be lower than fledging success (proportion of chicks hatched that survived until mid-September) and both can vary considerably by site. In Newfoundland, recent studies monitoring reproductive success (proportion of eggs laid that resulted in chicks that survived until mid-September) report higher reproductive success than in the early 1980s (Pollet et al. 2019a), suggesting that breeding conditions have improved. In contrast, Leach’s Storm-Petrels breeding in Nova Scotia and New Brunswick currently experience more variable annual reproductive success rates than reported prior to 1988, which may be due to negative effects of increasing ocean temperatures on foraging success during the breeding season (Pollet 2017; Mauck et al. 2018). Hatching and fledging success were higher in burrows surrounded by other occupied burrows, and occupied burrows tend to occur in areas of higher burrow density, suggesting that colonial living plays an important role for this species (Stenhouse and Montevecchi 2000; Fricke et al. 2015).

Chicks fledge on their own at night, aged 58-77 days (Mauck and Ricklefs 2005; Pollet et al. 2019a). Fledging occurs between mid-September and end of November, with some adults continuing to visit the burrow during the week after the chick has fledged (Pollet et al. 2019a).

Mortality appears to be highest during the first six months after the young leave the colony (Pollet et al. 2019a). Little is known about the pre-breeding years of Leach’s Storm-Petrel, although, based on genetic studies, pre-breeders appear to disperse widely across the Atlantic Ocean and may visit several colonies before choosing one in which to breed (Bicknell et al. 2013; see Dispersal and Migration below).

Physiology and adaptability

Leach’s Storm-Petrel has a remarkable ability to undertake long foraging trips, showing extreme foraging range (Pollet et al. 2014). In addition, they are uniquely adapted to forage at night and feed on vertically migrating bioluminescent fish (Hedd and Montevecchi 2006; Hedd et al. 2009), thus avoiding competition with diurnal pelagic seabirds. However, because they feed on bioluminescent fish, Leach’s Storm-Petrel may have evolved to seek light sources at night, making it susceptible to attraction to artificial lights (see Threats Category 9.6: Excess Energy and Category 3.1: Oil and Gas Drilling).

Diet and foraging behaviour

Leach’s Storm-Petrel is a surface-feeder, pecking at prey items while hovering or pattering on the sea surface, and congregating at upwellings and ephemeral convergence lines (Brown 1988; Pollet et al. 2019a). Fish dominates the Atlantic Leach’s Storm-Petrel’s diet (90% of reconstructed mass) at Newfoundland colonies, with mature lantern fish (Myctophidae) and sand lance (Ammodytes spp.) being most commonly fed to chicks; the remainder of the diet is primarily crustacea (amphipods and euphausiids; Hedd and Montevecchi 2006; Hedd et al. 2009). Dietary studies from colonies in New Brunswick and Nova Scotia show higher proportions of crustaceans (particularly euphausiids) and lower proportions of lantern fish (Frith et al. 2020), compared to colonies in Newfoundland (Hedd et al. 2009).

At-sea surveys confirm high densities of Atlantic Leach’s Storm-Petrels between near-shore colonies and offshore feeding sites during the breeding season (April-November; Figure 6a,b).

Dispersal and migration

Adult Atlantic Leach’s Storm-Petrels that have successfully raised a chick leave the colony between mid-September and mid-October (Pollet 2017), with some breeders staying as late as November (Fifield unpubl. data). Failed breeders may leave the colony earlier. Many storm-petrels migrate first to European waters, where peak numbers in November and December exceed the size of the European population alone, notably in the Bay of Biscay, France (Hémery and Jouanin 1988).

Data obtained from a limited number of deployed geolocators suggest that about two-thirds of breeding-aged Atlantic Leach’s Storm-Petrels winter in equatorial waters, mainly in the North Atlantic, circling in a clockwise pattern east across the Atlantic Ocean during fall migration, south to their wintering area, and returning north to the colony during the spring migration; the remaining one-third appear to travel as far south as the waters off South Africa to overwinter (Pollet et al. 2019b; Hedd unpubl. data; Figure 4). Leach’s Storm-Petrel is virtually absent from Canadian waters outside the breeding period (December-March; Figure 6c). No information is currently available on fidelity to wintering areas.

Unlike breeding adults, which show high breeding site philopatry (Fricke et al. 2015), pre-breeding Atlantic Leach’s Storm-Petrels exhibit low natal philopatry, as shown through genetic studies which suggest that Leach’s Storm-Petrel colonies across the Atlantic Ocean act as one metapopulation with high natal dispersal (Bicknell et al. 2012; 2013). Banding studies on Kent Island further corroborate high natal dispersal, where only ∼1% of >10,000 chicks banded were later found breeding on the island (Pollet et al. 2019a; Mauck pers. comm. 2020).

Figure 6. At-sea distribution of Atlantic Leach’s Storm-Petrel in waters off Atlantic Canada, during the breeding period (Panel a. April-July; and Panel b. August-November), and during the non-breeding period (Panel c. December-March). Map prepared by C. Gjerdrum based on information in the Atlas of Seabirds at Sea in Eastern Canada 2006-2016 (Environment and Climate Change Canada 2016).

Interspecific interactions

In Newfoundland and the nearby colony in the French territory of Saint-Pierre et Miquelon, nesting Atlantic Puffins are encroaching on areas used by breeding Atlantic Leach’s Storm-Petrel and thereby reducing the amount of available habitat (Lormée et al. 2012; Wilhelm et al. 2015, 2020).

In Canada, the most common avian predators on Atlantic Leach’s Storm-Petrel are Herring and Great Black-Backed Gulls, which prey on adults (Stenhouse et al. 2000; Bond unpubl. data). Corvids, namely Common Raven (Corvus corax) and probably American Crow (C. brachyrhynchos), prey upon adults, eggs, and chicks by digging out burrows (Pollet et al. 2019a). Remains of Atlantic Leach’s Storm-Petrel have been found in pellets of Great-Horned Owl (Bubo virginianus) and Short-Eared Owl (Asio flammeus; Holt 1987; Pollet and Shutler 2019).

Mammalian predators prey upon adults, eggs and chicks, and include American Mink (Neovison vison), River Otter (Lontra canadensis), Meadow Vole (Microtus pennsylvanicus), and Red Fox (Sklepkovych 1986; Pollet et al. 2019a; Rock unpubl. data). see Category 8.2: Problematic Native Species.

Population sizes and trends

Sampling effort and methods

A total of 106 colonies have been identified as either currently or previously supporting breeding Atlantic Leach’s Storm-Petrel in eastern Canada (Appendix 1), using one of the following methods.

Complete hole count

At sites where the entire island can be searched for storm-petrel holes, the most accurate approach to survey small Atlantic Leach’s Storm-Petrel colonies is by assessing all holes leading to burrows and multiplying the proportion of occupied burrows by the total number of holes counted. The most common method to determine the status of a burrow is through “grubbing”, where the observer inserts an arm down each hole to assess its contents, and assigns each hole to one of the following categories: 1) extra entrance or entrance to another burrow, 2) too short to be a burrow (< 30 cm), or 3) burrow and status (empty, adult, adult and egg, egg only, adult and chick, chick only, or could not be determined). Burrow occupancy is then derived by calculating the proportion of occupied burrows (i.e., burrows containing an adult and/or an egg or chick) in relation to all burrows where contents were assessed (i.e., occupied burrows and empty burrows, but excluding entrances, burrows too short, or burrows where the contents could not be determined; Robertson et al. 2002; Wilhelm et al. 2015). Active burrows can also be detected through the use of playback, where Leach’s Storm-Petrel calls recorded on a handheld device are played for several seconds at the mouth of a burrow; if a bird responds the burrow is deemed to be occupied. Correction factors are applied to occupancy estimates generated through playback techniques to account for the proportion of birds that fail to respond (Ambagis 2004).

Grid or transect approach

For larger colonies where complete hole counts are not feasible, the following standardized approaches are used, with details presented in Robertson et al. (2002) Lormée et al. (2012), Wilhelm et al. (2015), and d’Entremont et al. (2020). Island-wide grids or transects are established to: 1) determine or refine the area occupied by storm-petrels; and 2) measure occupied burrow density through plot assessments. Island-wide grids or transect lines are typically set 25-100 m apart and a minimum of 100 plots (ranging in area from 9-28.27 m²) are established at grid intersections, or at regular or random intervals along a transect line. All Leach’s Storm-Petrel holes within each plot are assessed through grubbing, as described above, and the occupied burrow density for each plot is calculated by multiplying occupancy rates by the burrow density of each plot. Population size estimates are obtained by multiplying the mean occupied burrow density by the estimated area occupied by storm-petrels.

Since 2011, a Geographic Information System (GIS) approach has been used to estimate area occupied by Atlantic Leach’s Storm-Petrels, thereby fine-tuning the delineation of occupied area and improving population estimates (e.g., Wilhelm et al. 2015). On large and convoluted colonies where Leach’s Storm-Petrel nests on slopes, maps of contour lines are incorporated into the GIS approach to provide more accurate estimated areas on slopes (e.g., Wilhelm et al. 2015, 2020). Because traditional non-GIS approaches can significantly underestimate the calculated sloped area occupied by storm-petrels compared to a GIS approach, it is important to ensure that previous survey methods yield comparable occupied area estimates prior to conducting a population trend analysis (e.g., Wilhelm et al. 2015, 2020).

Acoustic recording devices

Although Leach’s Storm-Petrels are generally quiet during the daytime, they vocalize freely in colonies at night (Pollet et al. 2019a). Automated acoustic recording devices placed on islands suspected of supporting Leach’s Storm-Petrel can be used to confirm that birds are present and possibly breeding (Buxton and Jones 2012). This approach has been used since 2014 to confirm the presence of Atlantic Leach’s Storm-Petrels that are likely breeding at low densities on remote islands along Quebec’s North Shore and in Nova Scotia (Rail pers. comm. 2019; d’Entremont pers. comm. 2020). This approach is limited as a survey tool as it can only indicate the presence of storm-petrels, and confirming that storm-petrels are breeding requires finding burrows and assessing their contents. Furthermore, caution is required in interpreting acoustic survey results, as the relationship between call-rates and relative abundance of breeding Leach’s Storm-Petrel varies across habitat types (Gladwell 2019).

Abundance

Most Atlantic Leach’s Storm-Petrel population estimates are published as numbers of breeding pairs. For the purpose of this report, we assume that one breeding pair equals two mature individuals, and have multiplied all breeding pair estimates by a factor of two. The current eastern Canadian population is estimated at about 5,277,000 mature individuals, with a range of 4,235,000-5,954,000 mature individuals, when considering the 95% confidence intervals for the major colonies where this information is available (Appendix 1).

There are 82 recent colonies in eastern Canada where breeding Atlantic Leach’s Storm-Petrels were present when the colony was last surveyed or checked, at some time since 1970, and which are presumed to be active (Appendix 1). An additional 11 historical and small colony sites have not been surveyed or checked since 1970, which may still be active, giving a range of 82-93 active colony sites in eastern Canada (Table 1; Figure 2; Appendix 1). Most of the active breeding population occurs in insular Newfoundland (93%; Table 1; Figure 2; Appendix 1), including Baccalieu Island, the world’s largest Leach’s Storm-Petrel colony (Wilhelm et al. 2020). Twenty islands in eastern Canada support colonies of more than 2,000 mature individuals (14 in insular Newfoundland, five in Nova Scotia and one in New Brunswick), which collectively host 99.7% of the regional population (Appendix 1).

There are an additional ten unoccupied colony sites which have hosted breeding storm-petrels within the past three generations (44 years), but where none were present when last visited (see Extent of Occurrence and Area of Occupancy; Figure 5; Appendix 1). Most abandonments were in Quebec (Figure 5, Appendix 1), possibly as a result of recent occurrences there of Red Fox (Vulpes vulpes) and American Mink (Neovison vison; Rail pers. comm. 2019).

Fluctuations and trends

There is no evidence from colony surveys and field research in Atlantic Canada that breeding numbers of Atlantic Leach’s Storm-Petrel are subject to population fluctuations, defined as rapid and frequent changes in the distribution or number of mature individuals. Paleo-ecological studies suggest that natural variation in breeding numbers may occur at some colonies, but these periods of growth and decline happen very gradually over a long period of time (i.e., hundreds to thousands of years; Duda et al. 2020a,b).

Trend assessments presented below are based on results of repeated surveys at colonies that together represent about 91% of the Atlantic Leach’s Storm-Petrel breeding population in Canada (Robertson unpubl. data; Appendix 1).

Insular Newfoundland

Robertson et al. (2006) conducted the first province-wide trend assessment of Atlantic Leach’s Storm-Petrels breeding in Newfoundland, accounting for any changes in survey and analytical methods. They found that the population size of three very large colonies (Gull, Great, and Green Islands; 100,000-1,000,000 mature individuals) showed little change between 1978 and 2001. However, two smaller colonies (Middle Lawn and Small Islands; 2,000-60,000 mature individuals) showed significant declines between 1981 and 2001 (Robertson et al. 2006). Since the early 2000s, significant efforts have been made to update the status and trends of Atlantic Leach’s Storm-Petrels breeding at most major colonies in the province (Appendix 1). Recent trend analyses revealed that all six Newfoundland colonies for which reliable population estimates are available, including the three largest in eastern Canada, have declined by the following annual rates: Baccalieu Island: -2.1% (1984-2013), Gull Island: -1.4% (1979-2012), Great Island: -2.0% (1979-2011), Small Island: -12.3% (1984-2018), Middle Lawn Island: -1.3% (2001-2016), and Green Island: -1.9% (2001-2015; Figure 7; Appendix 2).

Figure 7. Population trends and associated 95% credible intervals of six Atlantic Leach’s Storm-Petrel colonies in Newfoundland (Gull, Great, Baccalieu, Small, Middle Lawn, and Green Islands) from 1979 to 2018 (Robertson unpubl. data, based on information in Appendix 2). Colony size on the y-axis is shown on a log₁₀ scale.

Nova Scotia and New Brunswick

Trend information is available for two of the six largest Leach’s Storm-Petrel colonies in the Maritime Provinces, namely Bon Portage Island, located at the southern tip of Nova Scotia near the mouth of the Bay of Fundy, and Kent Island, part of the Grand Manan Archipelago on the New Brunswick side of the Bay Fundy (Figure 2). Trend analyses revealed annual population declines of -1.3% for Bon Portage Island (1983-2017) and -1.8% for Kent island (2000-2018; Figure 8; Appendix 2).

Figure 8. Atlantic Leach’s Storm-Petrel population trends and associated 95% credible intervals of colonies on Bon Portage Island, Nova Scotia and Kent Island, New Brunswick, from 1983 to 2018 (Robertson unpubl. data, based on information in Appendix 2). Colony size on the y-axis is shown on a log₁₀ scale.

Quebec

There are fewer than 20 records of Atlantic Leach’s Storm-Petrel breeding sites in Quebec (Appendix 1). Colonies are small (<2,000 mature individuals), with burrows often widely dispersed and hidden in dense vegetation, making it difficult to obtain reliable colony size estimates. However, some trend information comes from regular surveys in Migratory Bird Sanctuaries on the North Shore of the Gulf of St. Lawrence. Leach’s Storm-Petrel colonies were detected in four sanctuaries in the 1980s, and in 1988 and 1993 they collectively totalled about 1,800 mature individuals. Very few breeding pairs have been documented at these sites since then, with several colonies apparently abandoned (Figure 9; Appendix 1; Rail unpubl. data).

Figure 9. Population trends as indicated by the number of active nesting burrows in four Atlantic Leach’s Storm-Petrel colonies in Quebec, at Corossol Island, Wolf Bay, Boat Islands, and St. Mary’s Islands Migratory Bird Sanctuaries, from 1982 to 2016 (Rail unpubl. data).

Overall population trends

New trend analyses were undertaken by G.J. Robertson for this status assessment of eight Atlantic Leach’s Storm-Petrel colonies monitored in eastern Canada that had two or more colony surveys with estimates of survey error. These include all major colonies in eastern Canada, and account for about 91% of the eastern Canadian population. Colonies surveyed during the 3-generation time period 1974-2018 (44 years) were selected (Appendix 2). This period includes the time when the first statistically defensible colony surveys were conducted. Colonies without estimates of error were excluded, as there was no means of assessing the precision of the survey or whether the methods used were appropriate. Details of the analysis are provided in Appendix 3.

The overall trend for the eight Atlantic Leach’s Storm-Petrel colonies assessed declined at a rate of -1.74%/year, based on available surveys within the 3-generation period 1974-2018 (44 years; 95% CI: -2.35% to -1.08; Figure 10). The variance among colonies in their trend was small (σ_trend = 0.005, 95% CI: 0.001-0.015), which is reflected visually in the similar trends among colonies (Figures 7, 8). This change is the equivalent of a reduction in the population of -53.8% (95% CI: -38.0% to -64.9%) over three generations. Considering only the last 30 years (1988-2018), or two generations, a steeper but less certain decline of -2.64%/year (95% CI: -5.47%/year to +0.2%/year) is estimated, equivalent to a reduction of -55.2% (95% CI: -81.5% to +6.2%) over two generations.

Figure 10. Population trends and associated 95% credible intervals at eight Atlantic Leach’s Storm-Petrel colonies in eastern Canada, from 1979 to 2018. Dotted lines connect different survey dates for individual colonies, and solid black line depicts the overall trend over the past three generations (-1.74%/year; Robertson unpubl. data, based on information in Appendix 2). Colony size on the y-axis is shown on a log₁₀ scale.

Further analysis was undertaken to examine the uncertainty in these population trends and the implications of that uncertainty related to estimates of population reduction over three generations. Each value in the posterior distribution of the trend (β₁) was raised to the 44^th power (and thus projected over three generations), and that distribution was plotted with thresholds for a 30% decline (the threshold for Threatened under COSEWIC criterion A2) and a 50% decline (Endangered threshold under A2). Of the 30,000 MCMC outputs of the state-space model to estimate trends, 74.9% of the time the estimated trend was equivalent to a population reduction of 50% or more over three generations, and 99.3% of the time the estimated trend was equivalent to a population reduction of 30% or more over three generations (Figure 11).

Figure 11. Posterior distribution of population trends (β₁) for Atlantic Leach’s Storm-Petrel projected over three generations (44 years), estimated from a simple Bayesian state-space model (Appendix 3), using survey data from eight major colonies in Eastern Canada surveyed with statistically defensible methods (1974-2018). Thresholds are overlaid for declines of 30% over three generations (orange – Threatened under COSEWIC criteria A2, A4) and 50% (red – Endangered under COSEWIC criteria A2, A4), showing the probabilities of falling above or below those thresholds.

The steep population decline observed over the past two generations is consistent with observations that trends at large Leach’s Storm-Petrel colonies in Newfoundland were relatively stable until the early 2000s (Robertson et al. 2006), but experienced declines since then of ∼-40%, attributed in part to high levels of gull predation at two of the largest colonies (Gull and Great Islands; Wilhelm et al. 2015; Wilhelm 2017; Bond unpubl. data). Two large colonies in the Maritime provinces, Bon Portage and Kent Islands, have shown marked declines in just over one generation (-20% over 16 years, and -16% over 17 years, respectively), due to factors that are not clearly understood (Pollet and Shutler 2018; d’Entremont et al. 2020; see Threats). The large Atlantic Leach’s Storm-Petrel colony on Baccalieu Island has only been surveyed during two time periods (1984-1985 and 2013), so timing and magnitude of a two-generation decline on this population remains unknown, but Baccalieu shows very steep declines overall, similar to other large colonies (Wilhelm et al. 2020). Duda et al. (2020b) recently reconstructed the past 1,700 years of Baccalieu Island’s Leach’s Storm-Petrel population, using paleo-environmental approaches. They showed that numbers were much lower historically, increased from the late 19^th century throughout the 20^th century with a peak in the mid-1980s, followed by a rapid decline, thereby corroborating recent population trends estimated using traditional colony survey methods (Duda et al. 2020b).

Trends in neighbouring countries

Saint-Pierre et Miquelon, France

Grand Colombier Island, located 20 km off Newfoundland’s Burin Peninsula, currently hosts the second largest Atlantic Leach’s Storm-Petrel colony in the northwest Atlantic, but belongs to the French territory of Saint-Pierre et Miquelon. Lormée et al. (2012) estimated the population of Grand Colombier at 727,574 mature individuals in 2008, more than double previous estimates from surveys conducted in the late 1980s and 2004, of ∼356,000 and ∼286,000 mature individuals, respectively (Desbrosse and Etcheberry 1989; Robertson et al. 2006). More recently, this colony was estimated at 292,426 mature individuals in 2011 (Appendix 1). Closer examination of these estimates revealed significant discrepancies in estimates of the overall colony area used by Leach’s Storm-Petrels, which in this case, is most of Grand Colombier Island, prompting a re-analysis of previous surveys using a GIS approach to estimate occupied area (note: the survey in the late 1980s could not be re-analyzed due to insufficient information on how data were collected and the limited sampling effort as described by Desbrosse and Etcheberry 1989). Revised estimates suggest that the population size on Grand Colombier Island has ranged between about 347,000 (2004) and 507,000 (2008) mature individuals, with the most recent survey in 2011 resulting in an estimate of 400,000 mature individuals (Duda et al. 2020a). Results of the recent surveys, together with the original survey in the late 1980s, suggest variable but overall relatively stable numbers of breeding Leach’s Storm-Petrel on Grand Colombier Island.

As with several large eastern Canadian colonies, terrestrial habitat for Atlantic Leach’s Storm-Petrel breeding on Grand Colombier Island is declining in extent as a result of increases in the number of breeding Atlantic Puffins, which are encroaching on areas previously occupied by storm-petrels (Lormée et al. 2012). The presence of large gulls and Meadow Voles also affects the quality of storm-petrel breeding habitat on Grand Colombier. However, there is no indication that gull numbers are increasing, and overall impacts of gulls and voles on storm-petrels are thought to be minimal (Lormée et al. 2012).

Maine, United States

The coastal islands of Maine host over 99% of the United States’ Atlantic Leach’s Storm-Petrel population, with over 80% breeding at two colonies (Great Duck and Little Duck Islands; Schubel et al. 2019a). Based on the results of systematic surveys conducted at six major Maine colonies in 2018-19, the overall population trend in Maine appears to be increasing. Of six colonies surveyed, one declined (linked to the presence of mammalian predators), two were stable, and three increased significantly (Schubel et al. 2019b). The current estimate indicates 53,528 mature individuals breed on Great Duck and Little Duck Islands (Schubel et al. 2019b), more than double the previous estimate of 20,732 mature individuals reported for the 1990s (Chilelli 1999). Despite this apparent increase, the quality of breeding habitat on Great Duck Island appears to have declined over the long term, due to grazing by Snowshoe Hare introduced to the island in the 1960s (Schubel et al. 2019a).

Rescue effect

Atlantic Leach’s Storm-Petrel colonies throughout the North Atlantic basin likely act as a single metapopulation through appreciable eastward and westward exchanges of pre-breeding Leach’s Storm-Petrels among widely separated colonies (see Population Spatial Structure and Variability; Bicknell et al. 2012; 2013). The large and apparently stable Atlantic Leach’s Storm-Petrel colony on Grand Colombier, Saint-Pierre et Miquelon, France (Duda et al. 2020a) and Maine’s small, expanding population (Schubel et al. 2019b) could potentially serve as source populations for some declining colonies in Atlantic Canada. However, Grand Colombier and Maine currently only represent ∼8% of the total Atlantic Ocean Leach’s Storm-Petrel population (Table 2). Furthermore, the small populations in most Northeast Atlantic colonies are declining overall (Newson et al. 2008; Hansen unpubl. data), and St. Kilda, Scotland may be a population sink due to high predation by Great Skua (Catharacta skua) on non-breeding Leach’s Storm-Petrels, likely including those that have immigrated from colonies elsewhere in the Atlantic basin, including Canada (BirdLife International 2018). Hence, with major population declines on both sides of the Atlantic Ocean, and because eastern Canada hosts about 91% of the Atlantic Ocean population (Table 2), rescue from colonies outside Canada is very unlikely.

Pacific Leach’s Storm-Petrels breeding on the west coast of Canada are considered here to be a separate geographically disjunct DU (see Population Spatial Structure and Variability), and thus could not serve as a rescue population.

Threats and limiting factors

Threats

Specific causes of Atlantic Leach’s Storm-Petrel population decline are currently unknown, but are likely multi-factorial. Major threats faced by Leach’s Storm-Petrels at their breeding colonies include predation by native species and habitat loss or degradation. At sea, the species is primarily threatened by light pollution, activities associated with oil and gas production, severe weather conditions, and predicted disruptions in food availability as a result of climate-induced oceanic change.

These threats are categorized below, following the IUCN-CMP (International Union for the Conservation of Nature – Conservation Measures Partnership) unified threats classification system (based on Salafsky et al. 2008). They are listed in order of decreasing severity of impact (greatest to least), ending with those for which scope or severity is unknown. The overall threat impact is considered to be High, corresponding to an anticipated further decline of between about 10-70% over the next three generations (Master et al. 2012; see Appendix 4 for details).

Category 3.1: Oil and gas drilling (medium threat impact)

Many seabirds, including Leach’s Storm-Petrel, aggregate around offshore structures, attracted by food availability, night lighting, and other visual cues. This increases their risk of mortality from physical impacts with structures, strandings on structures, predation by avian predators, incineration from flares, disorientation, and unnecessary energy expenditure (Wiese et al. 2001; Montevecchi 2006; Burke et al. 2012, Ronconi et al. 2015). Effects of lighting and flares are linked to Category 9.6: Excess Energy (see below). In Atlantic Canada, Leach’s Storm-Petrel is the species most frequently recorded stranded on offshore platforms (90% of reports), with peak strandings in September and October (Gjerdrum et al. 2018). This coincides with the fledging period, suggesting that many storm-petrels affected have recently fledged from Canadian colonies.

Four offshore petroleum production facilities currently operate in waters of Newfoundland and Labrador (C-NLOPB 2019) and two in Nova Scotia waters (CNSOPB 2019). The foraging ranges of at least three of the largest Atlantic Leach’s Storm-Petrel colonies in eastern Canada overlap with these offshore oil and gas fields during the breeding season (Hedd et al. 2018). Leach’s Storm-Petrel is also threatened by offshore oil and gas activities on its wintering grounds off the coasts of western Africa and eastern Brazil (Pollet et al. 2019b; Hedd unpubl. data). As demand for oil and gas continues to rise to meet the needs of the world’s increasing human population (International Energy Agency 2016), threats from offshore production facilities to Leach’s Storm-Petrel are likely to continue to increase.

Category 8.2: Problematic native species (medium threat impact)

Avian predators are a direct threat to Atlantic Leach’s Storm-Petrels at several of the largest colonies in eastern Canada. Studies have shown that large gulls, primarily Herring Gulls, killed close to 49,000 adult storm-petrels on Great Island, Newfoundland in 1997 (Stenhouse et al. 2000) and over 110,000 adults on Gull Island, Newfoundland in 2012 (Bond unpubl. data). Predation rates were highest in May and June and decreased when spawning capelin moved inshore, reflecting a dietary shift by gulls to small fish (Stenhouse and Montevecchi 1999). Gulls likely take breeding Leach’s Storm-Petrels early in the nesting season, and non-breeding storm-petrels later when they prospect at colonies (Stenhouse and Montevecchi 1999). Predation thereby impacts both adult survival (Fife et al. 2015) and recruitment.

Herring Gull numbers declined across eastern Canada following the groundfish fishing moratorium which began in 1992, as a result of reduced anthropogenic food sources (Wilhelm et al. 2016). However, some gull colonies still have access to food subsidies through human sources, such as mink farms, garbage dumps, fishing vessels, and fish processing facilities (Bennett et al. 2017; Shlepr 2017) which may result in some gull colonies still being maintained locally at artificially high levels (Ronconi pers. comm. 2020; Wilhelm pers. obs.). Despite the overall gull population decline, some Leach’s Storm-Petrel colonies in eastern Newfoundland continue to experience high predation by gulls (Stenhouse et al. 2000; Bond unpubl. data). Gull predation also occurs at colonies in Nova Scotia and New Brunswick (Steenweg et al. 2011; Fife et al. 2015) and may influence nest site use (d’Entremont et al. 2020), although population-level impacts are unknown. Atlantic Leach’s Storm-Petrel may experience future increased gull predation, as ongoing oceanic climate changes decrease the availability of forage fish near some seabird colonies (Regular et al. 2014; Fitzsimmons et al. 2017).

Increasing populations of Atlantic Puffin in eastern Canada are reducing the availability of suitable storm-petrel nesting habitat because puffins excavate nest burrows in habitats used by nesting Atlantic Leach’s Storm-Petrels. Such encroachment has been observed at the three largest Atlantic Leach’s Storm-Petrel colonies in Newfoundland; Baccalieu, Gull and Great Islands (Wilhelm et al. 2015, 2020; Wilhelm unpubl. data).

Great Horned Owls are known predators of Leach’s Storm-Petrel at colonies such as Bon Portage Island, Nova Scotia (e.g., Pollet and Shutler 2019). Great Horned Owl numbers increased across eastern Canada from 1996 to 2003 (Artuso et al. 2013) and may be an increasing threat to Atlantic Leach’s Storm-Petrel.

Predation by native mammals occurs at several colonies in eastern Canada. Red Fox may have contributed to recent declines in Quebec (Rail pers. comm. 2019). While a resident Red Fox population was present on Baccalieu Island, it was estimated that foxes consumed 31,000 individual storm-petrels annually, although they likely deterred gulls from nesting on the island (Sklepkovych 1986). That fox population was extirpated sometime between 1985 and the early 2000s (Montevecchi pers. comm. 2020), and a small Herring Gull colony (about 50-100 pairs) has since become established (Wilhelm et al. 2020). Country Island, Nova Scotia has a resident population of Meadow Voles which have been observed foraging on eggs, removing eggs from burrows and eating dead chicks (Rock pers. comm. 2019).

Category 9.6: Excess energy (medium-low threat impact)

Light pollution is one of the most rapidly increasing human-related activities producing global alterations to the natural environment (Cinzano et al. 2001), and onshore artificial lights near Leach’s Storm-Petrel colonies are significant potential mortality sources. These largely nocturnal seabirds are attracted to artificial light, which may cause them to become disoriented, susceptible to collisions with human-made structures and vehicles, or forced to land on the ground where they are prone to starvation, dehydration, and predation (Le Corre et al. 2002; Miles et al. 2010; Rodriguez et al. 2014, 2017, 2019). Land-based light sources include lighthouses, residential communities, and industrial sites. Most seabirds attracted to lights on land are naïve fledglings going to sea for the first time (Le Corre et al. 2002; Miles et al. 2010; Rodríguez et al. 2017). In October 2018, over 500 Atlantic Leach’s Storm-Petrel carcasses were collected over two nights at two industrial sites in southern Conception Bay, Newfoundland; all but one were fledglings which likely had just departed from Baccalieu Island and died due to trauma caused by striking industrial buildings (Wilhelm unpubl. data).

Storm-petrels become stranded on fishing, cargo, and seismic vessels at night, often as a result of being attracted or confused by their lights (Ellis et al. 2013; Gjerdrum unpubl. data; Wilhelm pers. obs.). Light pollution from offshore oil and gas production facilities is an increasing threat for Atlantic Leach’s Storm-Petrel in both its summer and wintering areas (see Category 3.1: Oil and Gas Drilling).

Category 11.1 Habitat shifting and alteration (medium-low threat impact)

The Northwest Atlantic ecosystem underwent major changes in demersal and pelagic food webs following a cold-water event in the early 1990s, caused by increased Arctic freshwater outflow, which affected the availability of key prey species to higher trophic levels (Head and Pepin 2010; Buren et al. 2014, 2018). This regime shift coincided with the collapse of Atlantic Cod (Gadus morhua) populations due to overfishing, further cascading effects of changes in the food web (Frank et al. 2005). Leach’s Storm-Petrels breeding in eastern Canada feed primarily on small fish and supplement their diet with crustaceans (see Diet and Foraging Behaviour). However, the diversity of crustaceans in their diet has declined since this cold-water event, with small euphausiid species disappearing altogether (Hedd et al. 2009). Feather-based measures of stable isotopes suggest no change in diet of wintering Leach’s Storm-Petrel over a 150-year period (Fairhurst et al. 2015), although ecosystem changes associated with abnormal water temperatures are likely to increase in the future as a consequence of climate change (Boyd et al. 2014).

Changing climatic conditions on breeding and wintering grounds can impact vital rates of migratory seabirds. Winter distribution of Atlantic Leach’s Storm-Petrel is positively associated with high sea surface temperature and high chlorophyll-a concentrations, at both productive upwelling areas and highly eutrophic coastal regions of equatorial and South Atlantic (see Marine Habitat Requirements). Long-term models predict that Net Primary Production in these regions will decrease (Boyd et al. 2014), thereby decreasing winter habitat quality and likely negatively affecting Leach’s Storm-Petrel survival. Because low adult survival is a key demographic factor contributing to Atlantic Leach’s Storm-Petrel population declines, potential influence of variation in Net Primary Production and other climate-induced changes in oceanographic conditions in storm-petrel wintering areas requires investigation.

Mauck et al. (2018) found that Atlantic Leach’s Storm-Petrel reproductive success follows a quadratic response to rising global mean temperatures, with hatching success increasing up to a critical point and then declining as the temperature continues to increase. Warming temperatures are thought to initially reduce thermoregulatory costs to incubating adults, but may indirectly reduce reproductive success once higher sea surface temperatures reduce prey availability within the foraging range (Mauck et al. 2018). This critical point has consistently been exceeded in the Gulf of Maine since 1988, resulting in variable breeding success at Kent, Machias Seal, and Bon Portage Islands (Mauck et al. 2018; Major unpubl. data; Pollet pers. obs.). Reproductive success has recently been consistently high at large colonies near the centre of the eastern Canadian breeding range (e.g., Gull and Baccalieu Islands), suggesting that current summer food supply is favourable (Hedd unpubl. data). This may change in future if global temperatures rise as a result of climate change and negatively impact food availability.

Category 9.2: Industrial and military effluents (low threat impact)

Atlantic Leach’s Storm-Petrel is vulnerable to coming into contact with oil sheens on the ocean surface caused by chronic ship-source oil discharges, allowable operational discharges from offshore oil and gas activities, and accidental discharges of larger amounts of oil from production platforms (Fraser et al. 2006; Wilhelm et al. 2007; Ellis et al. 2013; Robertson et al. 2014; Morandin and O’Hara 2016). Oil pollution from offshore oil and gas production facilities is an increasing threat to Leach’s Storm-Petrel in both summer and wintering areas (see Category 3.1: Oil and Gas Drilling).

Leach’s Storm-Petrel is vulnerable to oil because it spends extended periods at sea, feeds over wide areas, and makes frequent contact with the ocean surface. Exposure to oil, including sheens, disrupts the structure of feathers, destroying the thermal insulation and buoyancy provided by air trapped by the feathers, and causing oiled birds to suffer from hypothermia or drown (Jenssen et al. 1985; O’Hara and Morandin 2010). Ingestion of oil, through preening or consuming contaminated food or water, causes internal organ malfunction and hematological changes (Alonso-Alvarez et al. 2007; Horak et al. 2017). While such internal effects may not always be lethal, they may affect an individual’s ability to reproduce successfully, by causing abnormal behaviours, decreased fertility, or premature death of offspring. Experimental studies of Leach’s Storm-Petrel showed reduced reproductive success following internal or external exposure to oil (Trivelpiece et al. 1984; Butler et al. 1988).

Category 9.4: Garbage and solid waste (low threat impact)

Marine debris, in particular plastic pollution, represents a growing threat to seabirds, including Leach’s Storm-Petrel (O’Hanlon et al. 2017). Leach’s Storm-Petrels ingest and retain small pieces of plastic in the gizzard, and breeding adults subsequently offload ingested plastics to their offspring (Rothstein 1973; Bond and Lavers 2013; Provencher et al. 2014), although a recent study suggests that high incidence of plastics in chicks did not preclude successful fledging (Krug 2020; Krug et al. 2020). In addition to direct negative impacts of having no nutritional value and damaging the digestive tract, ingested plastics may indirectly compromise the health of individuals through increased exposure to metals and other contaminants causing toxicity, which may negatively impact adult survival and reproductive success (reviewed in Lavers and Bond 2016; O’Hanlon et al. 2017).

Category 11.4: Storms and flooding (low threat impact)

Extreme weather events, such as storms of higher than normal intensity or duration, may flood nesting burrows with low drainage capability, and drown eggs or chicks that are present (Pollet et al. 2019a). Strong storms with onshore winds may blow Leach’s Storm-Petrels ashore, stranding numbers ranging from a few individuals to thousands (Cramp and Simmons 1977; Hémery and Jouanin 1988; Ruckdeschel et al. 1994; Megson et al. 2014). When such wrecks occur in September and October, they primarily affect fledgling birds, although moulting adults may also be vulnerable to mass strandings when severe onshore winds occur during fall migration (Hémery and Jouanin 1988). Increased frequency of extreme weather events during the fall could increase the impacts of mass strandings on juvenile survival and recruitment.

Category 8.1: Invasive non-native/alien species (low threat impact)

Domestic animals and introduced non-native mammals, such as rats (Rattus spp.) and Striped Skunks (Mephitis mephitis), can have devastating effects on Leach’s Storm-Petrel colonies. For example, Seal Island, off southern Nova Scotia, hosted a large Atlantic Leach’s Storm-Petrel colony during the early 1900s, which had been extirpated by 1959 due to predation by dogs, cats, rats, pigs, and skunks (Pollet et al. 2019a). American Mink were introduced to the island of Newfoundland through escapes or releases from commercial mink farms (Government of Newfoundland and Labrador 2019). Although mink are infrequently observed in Newfoundland, their presence can have devastating effects within storm-petrel colonies by killing significant numbers of breeding adults in a short period (Wilhelm pers. obs.; Fitzsimmons, pers. comm. 2019).

Category 7.3: Other ecosystem modifications (negligible threat impact)

Breeding habitat degradation through grazing by introduced Snowshoe Hare and White-tailed Deer has caused habitat changes on islands hosting two of the largest Atlantic Leach’s Storm-Petrel colonies in the Maritime Provinces: Kent and Bon Portage Islands (see Terrestrial Habitat). The browsing of young trees prevents forest regeneration in habitats used by breeding storm-petrels, and opens up the landscape for Herring Gulls to breed (Wheelwright 2016). While hare and deer are still present on Bon Portage Island (Shutler pers. comm. 2019), Snowshoe Hare was successfully eradicated from Kent Island in 2007 (Wheelwright 2016). Large-scale fisheries may affect marine community structure and food availability for seabirds (e.g., Cury et al. 2011), although most changes would be confined to shelf waters rather than deeper areas where storm-petrels usually forage during the breeding period (Hedd et al. 2018).

Category 6.1: Recreational activities (negligible threat impact)

Recreational activities, such as temporary camping and hiking, which occur on those islands that support breeding colonies but are not formally protected, could affect Leach’s Storm-Petrels by trampling nesting burrows and disturbing birds.

Category 6.3: Work and other activities (negligible threat impact)

Although designed to minimize effects on breeding Leach's Storm-Petrels, surveys and research activities on colonies throughout eastern Canada may disturb some nesting birds and their burrows; population-level effects are likely to be insignificant.

Category 3.3: Renewable energy (unknown threat impact)

Anticipated future development of offshore wind farms planned for the Gulf of Maine will have effects of yet-unknown scope and severity on Atlantic Leach’s Storm-Petrels breeding in Bay of Fundy and Gulf of Maine colonies (Stenhouse pers. comm. 2020).

Category 9.5: Air-borne pollutants (unknown threat impact)

Mercury is most toxic when transformed into methylmercury in marine or freshwater ecosystems. Methylmercury exposure can have negative neurological, immunological, behavioural, endocrine, and reproductive effects on marine organisms feeding at higher trophic levels, including seabirds (Wolfe et al. 1998; Scheuhammer et al. 2015). Elevated levels of mercury are consistently found in breeding Atlantic Leach’s Storm-Petrels (Bond and Diamond 2009; Pollet et al. 2017; Stenhouse et al. 2018), and Newfoundland storm-petrels appear to be exposed to higher mercury levels than those breeding in Nova Scotia and New Brunswick (Burgess unpubl. data). No relationship was found among mercury levels, reproductive success, and adult survival of Atlantic Leach’s Storm-Petrels breeding on Bon Portage Island, Nova Scotia (Pollet et al. 2017), although studies are underway to assess possible mercury impacts on reproduction and survival at those Newfoundland colonies with significantly higher mercury exposures (Burgess pers. comm. 2019).

Limiting factors

Leach’s Storm-Petrel is a k-selected species, characterized by high adult survival, delayed onset of maturity (first breeding at 6-7 years, on average), and low reproductive output (raising a maximum of one chick per year; Pollet et al. 2019a; see Life Cycle and Reproduction). Annual survival rates of such species tend to be high, and for procellariiform seabirds, they are typically over 0.90 (Schreiber and Burger 2001). Annual survival for Pacific Leach’s Storm-Petrel in British Columbia has been estimated at 0.975 ± 0.01 (Rennie et al. 2020). This contrasts markedly with Atlantic Leach’s Storm-Petrel, where apparent annual adult survival rates at colonies monitored across the eastern Canadian range since 2000 have been consistently low (∼0.78-0.86; Fife et al. 2015; Pollet et al. 2019a; Fraser and Russell unpubl. data; Hedd unpubl. data). Low annual adult survival is likely a key factor contributing to current population declines of Atlantic Leach’s Storm-Petrel (see Life Cycle and Reproduction).

Individual Leach’s Storm-Petrels appear to exhibit high fidelity to their breeding sites once they begin to breed (see Life Cycle and Reproduction), which may limit the population growth of specific colonies by preventing adults from moving to other colonies if local conditions are poor for adult survival (e.g., high predation rates) or reproductive success (e.g., chronic poor food availability).

High natal dispersal rates exhibited by Atlantic Leach’s Storm-Petrel are beneficial in increasing gene flow across the Atlantic Ocean (see Dispersal and Migration). However, this may also be a limiting factor if the emigration of young birds from the eastern Canadian colonies, which host some of the largest breeding numbers in the north Atlantic (see Population Sizes and Trends), exceeds immigration from colonies in other countries.

Number of locations

Each location for Atlantic Leach’s Storm-Petrel is a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals present. The most serious plausible threat that could rapidly affect Atlantic Leach’s Storm-Petrel appears to be that posed by Problematic Native Species (Threat Category 8.2), related to the risk of predation at colonies from native predators, especially gulls, owls, foxes, voles and mink, and encroachment of other species, such as Atlantic Puffin, on storm-petrel breeding areas. Leach’s Storm-Petrel in eastern Canada nests on coastal islands, which reduces the risk of predation, especially from ground predators. However, these ground predators sometimes occur, even intermittently, on islands that support colonies. The threat posed by problematic native species is likely independent for each island, reflecting the likelihood of predators being present, the numbers present, colony size, and factors affecting the risk of predation, such as the type of nesting habitat. Each island is therefore a geographically distinct area in which this single threatening factor could rapidly affect all individual Leach’s Storm-Petrels present.

The number of active locations is considered to be 82-93, equal to the number of coastal island sites currently supporting active Atlantic Leach’s Storm-Petrel colonies in eastern Canada. There is evidence that the number of locations has been declining in Quebec and at scattered islands elsewhere in Atlantic Canada (Appendix 1). Most islands on which storm-petrels are no longer detected previously hosted very few mature individuals (usually 20 pairs or fewer). Furthermore, these remote colonies are only visited briefly and infrequently by researchers during the day, which may result in the presence of storm-petrel burrows being overlooked, especially on large islands (Rail pers. comm. 2019). However, an ongoing decline in the number of locations is considered likely, reflecting the loss of small colonies in Quebec and elsewhere.

Protection, status and ranks

Legal protection and status

Leach’s Storm-Petrel is protected in Canada under the federal Migratory Birds Convention Act 1994 (MBCA; Government of Canada 2017) and parallel legislation in the United States (USFWS 2016) and Mexico. The MBCA protects individual Leach’s Storm-Petrels, their nests and their eggs throughout Canada, and prohibits the dumping of substances that are deleterious to migratory birds in waters or areas frequented by them. Additional protection for this species is also afforded through provincial acts, namely: Fish and Wildlife Act (New Brunswick) and Wildlife Act (Nova Scotia and Newfoundland and Labrador). In Quebec, Leach’s Storm-Petrel is included on the list of wildlife species at risk of being designated threatened or vulnerable (Liste des espèces susceptibles d’être désignées menacées ou vulnérables; Gouvernement du Quebec 2019).

Non-legal status and ranks

At a global level, Leach’s Storm-Petrel is considered Vulnerable according to the IUCN Red List (IUCN 2016) and Secure (G5) by NatureServe (2019). Nationally, Leach’s Storm-Petrel is currently ranked as N4B (Apparently Secure, Breeding population; NatureServe 2019) in Canada. At the subnational level in the eastern Canadian provinces, Atlantic Leach’s Storm-Petrel is ranked as S2B (Imperilled, Breeding population) in Labrador, New Brunswick, and Quebec, S3B (Vulnerable, Breeding population) in Nova Scotia, and S4B (Apparently Secure, Breeding population) on Newfoundland Island (NatureServe 2019). The species is considered Secure (N5B) at the national level within the United States (US) breeding range (NatureServe 2019). It is considered Imperilled/Vulnerable (S2S3) in Maine, the US state bordering the species’ eastern Canadian breeding range (NatureServe 2019).

Leach’s Storm-Petrel is identified as a conservation priority species in one Marine Biogeographical Unit (MBU) in Newfoundland (MBU 10; Environment Canada 2013a), in two Bird Conservation Regions (BCRs) in Quebec (BCR 8 and 14; Environment Canada 2013b,c), in one MBU in New Brunswick (MBU 11; Environment Canada 2013d), and in two MBUs in Nova Scotia (MBU 11 and 12; Environment Canada 2013e).

Habitat protection and ownership

Of the 93 active Atlantic Leach’s Storm-Petrel colonies in eastern Canada, 29 are located on islands federally protected as Migratory Bird Sanctuaries or National Parks, or provincially protected as Wildlife Management Areas or Seabird Ecological Reserves (Appendix 1). In addition, three colonies are on privately owned islands operated as research stations (Bon Portage Island, Nova Scotia, owned by Acadia University and protected by a conservation easement between the university and the Nova Scotia Nature Trust, and Kent and Hay Islands, New Brunswick, owned by Bowdoin College). One colony is on Country Island, Nova Scotia, owned by the Department of Fisheries and Ocean’s Canadian Coast Guard and operated as a research station by ECCC-CWS. Collectively, these protected islands support 93% of the Atlantic Leach’s Storm-Petrel population in Canada (Appendix 1).

In the Maritime provinces, all known large (> 2,000 mature individuals) Atlantic Leach’s Storm-Petrel colonies are either legally protected under Nova Scotia’s Wildlife Act as Wildlife Management Areas or owned by crown or private organizations that focus on the conservation of wildlife (Appendix 1). In Newfoundland and Labrador, four of the largest colonies, including Baccalieu Island, the world’s largest colony, are protected under Newfoundland’s Wilderness and Ecological Reserves Act as Seabird Ecological Reserves. However, there are at least nine significant colonies with no protection, which host between 2,600 and potentially up to 200,000 mature individuals (Appendix 1). While some islands are likely too far from shore or are too steep to attract many human visitors (e.g., Coleman and Corbin Islands), others are easy to access and colonies may be experiencing some level of disturbance by local people due to recreational activities (e.g., berry picking, exploring). Most notably, the Little Fogo Islands, which host at least three colonies with over 3,000 mature individuals (see Fluctuations and Trends), are a resettled fishing community where remaining houses are used as summer cabins. Furthermore, several large colonies are located on islands with navigational aids or lighthouses, which require regular maintenance by the Canadian Coast Guard which may inadvertently disturb Leach’s Storm-Petrels. In particular, the lighthouse on Green Island, near Fortune Bay, Newfoundland and Labrador, which hosts about 100,000 mature individuals, is staffed year-round, therefore increasing the risk of chronic disturbance by humans and domestic animals, or the inadvertent introduction of non-native species.

Acknowledgements and authorities contacted

Acknowledgements

Support for the preparation of this report was provided by Environment and Climate Change Canada and Birds Canada, with funding from Atlantic Ecosystems Initiative Grant # GCXE18P018. It was initially submitted to COSEWIC as an unsolicited report by Environment and Climate Change Canada in October 2019. Andrew Horn, Elsie Krebs, Louise Blight, Syd Cannings, Jessica Humber, and Isabelle Gauthier provided constructive comments on earlier versions of this report. Richard Elliot, co-chair of the COSEWIC Birds Specialist Subcommittee (SSC), provided helpful feedback throughout the preparation, submission and revision of this unsolicited report. The authorities listed below provided valuable comments on a previous version as well as non-published information, including data, maps, and personal observations.

Authorities contacted

Sydney Allen. GIS and Scientific Project Officer, COSEWIC Secretariat, Environment and Climate Change Canada, Ottawa, Ontario.

Alex Bond. Senior Curator of Birds, Natural History Museum at Tring, Hertfordshire, United Kingdom.

Neil Burgess. Research Biologist, Wildlife and Landscape Science Directorate, Environment and Climate Change Canada, St. John’s, Newfoundland and Labrador.

Antony Diamond. Professor Emeritus, Department of Biology, University of New Brunswick, Fredericton, New Brunswick.

David Fifield. Marine Wildlife and Ecosystem Conservation Specialist, Wildlife and Landscape Science Directorate, Environment and Climate Change Canada, St. John’s, Newfoundland and Labrador.

Michelle Fitzsimmons. Postdoctoral Fellow, Wildlife and Landscape Science Directorate, Environment and Climate Change Canada, St. John’s, Newfoundland and Labrador.

Carina Gjerdrum. Wildlife Biologist, Canadian Wildlife Service, Environment and Climate Change Canada, Dartmouth, Nova Scotia.

Gail Fraser. Professor, Faculty of Environmental and Urban Change, York University, Toronto, Ontario.

Heather Major. Assistant Professor, Department of Biology, University of New Brunswick, Saint John, New Brunswick.

Robert Mauck. Director, Bowdoin Scientific Station at Kent Island, Bowdoin College, Brunswick, Maine.

William Montevecchi. Research Professor, Departments of Psychology and Biology, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador.

Jean-François Rail. Wildlife Biologist, Canadian Wildlife Service, Environment and Climate Change Canada, Quebec, Quebec.

Jen Rock. Wildlife Biologist, Canadian Wildlife Service, Environment and Climate Change Canada, Sackville, New Brunswick.

Robert Ronconi. Wildlife Biologist, Canadian Wildlife Service, Environment and Climate Change Canada, Dartmouth, Nova Scotia.

Janet Russell. Biologist, The Alder Institute, Tors Cove, Newfoundland.

Dave Shutler. Professor, Department of Biology, Acadia University, Wolfville, Nova Scotia.

Iain Stenhouse. Marine Bird Program Director, Biodiversity Research Institute, Portland, Maine.

Laura Tranquilla. Atlantic Program Manager, Birds Canada, Sackville, New Brunswick.

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Biographical summary of report writer(s)

Sabina I. Wilhelm is a seabird biologist with over 20 years of experience working on a variety of seabird species. She obtained her Ph.D. in 2004 from Memorial University’s Cognitive and Behavioural Program, and began working as a Wildlife Biologist with Environment and Climate Change Canada’s Canadian Wildlife Service in St. John’s, Newfoundland the same year. Sabina is currently leading the Colonial Seabird Monitoring Program for the Atlantic Region. Since 2011, her efforts have focused on monitoring the population status and trends of Atlantic Leach’s Storm-Petrels at various colonies in the Atlantic provinces, and she has published several peer-reviewed papers on the ecology and status of this species.

April Hedd has over 20 years of research experience with seabirds and is currently a research scientist with the Wildlife and Landscape Science Directorate of Environment and Climate Change Canada in St. John’s, Newfoundland. She earned a Ph.D. from the University of Tasmania, Australia in 1999, focused on the foraging ecology of Shy Albatrosses and their interactions with fisheries. Upon returning home to Newfoundland, she began studying Atlantic Leach’s Storm-Petrels as a post-doctoral fellow in 2002, and continues to work there today. Her work combines long-term demographic and food web studies with spatial and toxicological datasets to understand drivers of the species’ decline throughout the North Atlantic. April’s research interests lie in conservation ecology, in particular, in understanding how natural and anthropogenic factors influence distribution and population trends of marine birds.

Gregory J. Robertson has 30 years of experience researching and monitoring fish and wildlife populations, mainly in northern coastal and marine habitats. He obtained his Ph.D. from the Centre for Wildlife Ecology at Simon Fraser University, and started working as a federal research scientist in 1998 in St. John’s, Newfoundland. Greg is currently a senior research scientist with Environment and Climate Change Canada and the Department of Fisheries and Oceans, working on priority wildlife issues in coastal ecosystems, and quantitative stock assessments of commercially important groundfish. Greg re-initiated Atlantic Leach’s Storm-Petrel monitoring programs in Newfoundland in the early 2000s, and contributed the quantitative trend analysis to this assessment.

Ingrid L. Pollet received a technical diploma in agronomy in 1996 from Université Claude Bernard, in France. She subsequently immigrated to Canada where she worked in medical research for several years, eventually finding her passion in several songbird studies, before focusing her interest on seabirds. She recently completed her Ph.D. co-supervised at Acadia and Dalhousie Universities, studying the extrinsic factors that influence movement and reproductive success of Atlantic Leach’s Storm-Petrels. Ingrid has just completed a postdoctoral research position at Justus-Liebig University in Giessen, Germany.

Collections examined

No collections were examined for the preparation of this report.

Appendix 1. Most recent population estimates available of all active and historical (not assessed since 1970) Atlantic Leach’s Storm-Petrel breeding colonies in eastern Canada and Saint-Pierre et Miquelon, France, listed by colony name and province (LB = Labrador, NF = insular Newfoundland, NB = New Brunswick, NS = Nova Scotia, QC = Quebec) or region

Appendix 2. Estimated number of mature individuals and associated 95% confidence intervals, for the ten Atlantic Leach’s Storm-Petrel colonies in Newfoundland, Nova Scotia, and New Brunswick which were used to estimate the rate of population reduction over three generations for eastern Canada

Appendix 3. Details of population trend analyses developed for Atlantic Leach’s Storm-Petrel status assessment (G.J. Robertson unpubl. data.)

A simple state-space model was employed to assess population trend at colonies of Atlantic Leach’s Storm-Petrel in eastern Canada. The state of each colony (true population size at time t, x_t) cannot be directly observed, but rather estimates of the colony size and associated error are available in certain years (y_t ± σ_t). With annual estimates of colony size, a time series analysis which includes autocorrelation across years can be used to estimate trend, but for storm-petrels only 2-5 surveys were available over this 44-year period, so a simple Poisson regression was used to model trend.

A random effect was included for colony-specific trends, to account for possible differences from the overall trend across all colonies. Formally, the model took the following form, where t is time (or year) and c is colony:

x_ct∼Poisson(μ_ct)
E(x_ct) = μ_ct = μ_ct and Var(x_ct) = μ_ct
log(μ_ct) = β₀ + β₁ X t + β_2c X colony_c + b_c X colony_c x t
y_ct∼(x_ct, σ_ct)
b_c∼N(0,σ_trend)

Models were fitted in a Bayesian framework using JAGS (Plummer 2003), via the r2jags interface (Su and Yajima 2015). Vague priors were used for all regression parameters. Given that order-of-magnitude differences exist among the colony sizes (ranging from 100s to millions of individuals), non-zero starting values and priors for the reference level colony size (β₀) were supplied (∼12 on the natural logarithm scale), while other intercepts and trend were assigned priors with 0 mean, and variances of 10,000. The variance in the random effect for trend (σ_trend) was modelled with a prior based on a half (positive values only) Student's t distribution, with a mean of 0, a variance of 625 and four degrees of freedom (Robertson et al. 2017). Models were run with three Markov Chain Monte Carlo (MCMC) chains, each with 10,000 iterations, and a burn-in period of 5,000 iterations. Mixing was assessed after these 15,000 iterations, by visually examining MCMC chains and examining values of R-hat (which should be less than 1.1; Gelman et al. 2013). Posterior distributions of annual predicted values were also calculated and extracted for plotting purposes. In some cases, mixing was not well achieved, generally with one of the three chains taking a different trajectory. This was resolved by either running further iterations (another 10,000 or 20,000 iterations), or re-starting the model run and adjusting the initial value for the reference colony intercept. To calculate and plot colony specific trends, an additional interaction term (β_3c × colony_c × t) was added to the linear predictor, while the random effects in trend (b_c) were removed. Bayesian 95% credible intervals (CI), extracted from the posterior distributions of the MCMC chains, are presented for all parameter estimates.

Appendix 4. Threats calculator table for Atlantic Leach’s Storm-Petrel in Canada

Species or ecosystem scientific name:
Leach's Storm-Petrel (Atlantic Population)

Date (Ctrl + ";" for today's date):
13/01/2020

Assessor(s):
Sabina Wilhelm, April Hedd, Greg Robertson, Ingrid Pollet (report writers), Richard Elliot (SSC co-chair), David Fraser (facilitator), Marie-France Noël (COSEWIC secretariat), Courtney Baldo, Louise Blight, Neil Burgess, Josh Cunningham, Dave Fifield, Marcel Gahbauer, Carina Gjerdrum, Rielle Hoeg, Andy Horn, Jessica Humber, Elsie Krebs, Bob Mauck, Mark McGarrigle, Pam Mills, Bill Montevecchi, Allison Moody, Jean-François Rail, Michael Rodway, Rob Ronconi, Donald Sam, Dave Shutler, Iain Stenhouse, Laura Tranquilla

References:
Based on draft Leach's Storm-Petrel (Atlantic Population) status report (November 2019) and draft threat assessment calculator (January 2020)

Overall Threat Comments

Leach's Storm-Petrel (Atlantic Population) was assessed as one designatable unit. Generation time was assumed to be approximately 14.8 years.