Great Blue Heron fannini subspecies Ardea herodias fannini: addendum to the 2008 COSEWIC status report

Official title: Addendum to the 2008 COSEWIC status report on the Great Blue Heron fannini subspecies Ardea herodias fannini in Canada

Not applicable

2023

* Addendum to the 2008 COSEWIC status Report on the Great Blue Heron fannini subspecies (Ardea herodias fannini).

COSEWIC assessment summary

Assessment summary – May 2023

Common name: Great Blue Heron fannini subspecies

Scientific name: Ardea herodias fannini

Status: Not applicable

Reason for designation: Status is not assigned. This population is no longer a valid Designatable Unit, as it does not meet the 2020 revised COSEWIC criteria for discreteness and evolutionary significance and is, therefore, not eligible for COSEWIC status assessment.

Occurrence: British Columbia

Status history: COSEWIC: Designated Special Concern in April 1997. Status re-examined and confirmed in April 2008.

COSEWIC addendum

Ardea herodias fannini

Great Blue Heron fannini subspecies

Grand héron de la sous-espèce fannini

Range of occurrence in Canada: British Columbia

Current COSEWIC assessment

Status category

Addendum 1: SC

Addendum 2: Date of last assessment: April 2008

Addendum 3: Not applicable

Reason for designation at last assessment: In Canada, this subspecies is distributed along the coast of British Columbia with a relatively small population that is concentrated at a few breeding colonies in southern British Columbia. There is evidence of declines in productivity, and it is unclear whether the population is stable or declining. Threats from eagle predation, habitat loss and human disturbance are ongoing, particularly in the southern part of the range where concentrations of birds are highest.

Addendum 4: Criteria applied at last assessment: Not applicable

SSC recommendation

Addendum 5: Not applicable

Evidence: Not applicable, as this subspecies is considered ineligible for assessment

Wildlife species

Addendum 6: Change in eligibility, taxonomy or designatable units: Yes

Explanation: COSEWIC may recognize a Designatable Unit (DU) below the level of a taxonomic species and assess its status, if it is shown to have attributes that make it both discrete and evolutionarily significant (COSEWIC 2020). If no units meet the current criteria for discreteness and significance, the default option is for COSEWIC to consider the status of the taxonomic species in Canada as a whole. This Addendum to COSEWIC (2008) explores whether there is sufficient evidence to reject the null hypothesis that there is one Great Blue Heron DU in Canada, specifically considering evidence in support of a separate Pacific coast DU, aligned with the distribution of subspecies Ardea herodias fannini (hereafter fannini).

In previous COSEWIC status assessments (Butler 1997; COSEWIC 2008), the subspecies fannini, found on the Pacific coast of British Columbia, was recognized as a distinct DU on the basis of being a separate taxonomic subspecies from A. h. herodias (hereafter herodias). COSEWIC guidelines for recognizing DUs were revised in November 2020, and now require that DUs recognized on the basis of being separate subspecies must also meet updated criteria for both discreteness and evolutionary significance (COSEWIC 2020).

The revised DU guidelines set out two criteria for discreteness and two for evolutionary significance, and require that a DU must meet at least one criterion from each category (COSEWIC 2020). This Addendum to COSEWIC (2008) evaluates the available evidence as to whether the population of Great Blue Herons that occurs on the Pacific coast of British Columbia, considered to be subspecies fannini, meets the current criteria for recognition as a valid DU.

Subspecies structure

Two subspecies of Great Blue Heron occur in Canada, with fannini having a limited distribution on the Pacific coast and islands of British Columbia, and herodias occurring in most of the remainder of southern Canada (Vennesland and Butler 2011; re-published as Vennesland and Butler 2020). Some writers extend fannini into northwestern Washington (for example, Oberholser 1912), while others consider this area and southern British Columbia to be a zone of hybridization (for example, Vennesland and Butler 2011). The taxonomy of Great Blue Herons occurring farther south of fannini in the northwestern United States is unclear, and that subspecies has been variously considered to be A. h. treganzai (hereafter treganzai) in east-central Washington or A. h. hyperonca (hereafter hyperonca) to the south (Oberholser 1912); A. h. wardi (hereafter wardi; Vennesland and Butler 2011); and most recently, herodias (Dickerman 2004a,b; Cheek et al. 2018; McGuire et al. 2019).

The following sections describe differences in plumage, morphology, geographic distribution, population genetics, and migratory behaviour, between fannini and adjacent Great Blue Heron subspecies, which are then assessed from perspectives of discreteness and significance.

Plumage, morphology, and geographic distribution

The subspecies fannini was first described by Chapman (1901) on the basis of a type specimen from Skidegate, on Graham Island, Haida Gwaii, British Columbia, and the heads and necks of just two other birds from Haida Gwaii, all of which were described as darker and more intensely coloured than herodias. Based on the type specimen, Chapman (1901) suggested that the tibia of fannini was more feathered, although subsequent researchers have not noted this difference. Chapman (1901) noted that an adult male specimen from Sooke Lake, near Victoria, British Columbia, was somewhat lighter in coloration, indicating “the intergradation of fannini with herodias at a point further south,” but made no further comments on the range of fannini (Chapman 1901).

In his revision of Great Blue Heron taxonomy, Oberholser (1912) included the Pacific coast from Cook Inlet, Alaska, south to central-western Washington within the range of fannini, based on a small sample of eight individuals that he considered to be representative of this subspecies, including two from Washington state. He considered the dark northwestern fannini to be separable from herodias by its longer wing and tail, shorter tarsus and culmen, and much darker neck and upper parts. He considered fannini to be a permanent non-migratory resident, “except perhaps in the northern-most part of the range” (Oberholser 1912).

One specimen considered fannini by Oberholser (1912) was a breeding male from Nisqually Flats, northwestern Washington (19 April 1892), which had the longest wing, culmen, and tarsus of the ten “fannini” birds he measured. Its measurements readily fall within the ranges he gave for treganzai, the subspecies he considered to occur to the immediate south and southeast of fannini, including in “eastern Washington; west to central Washington (probably)” (Oberholser 1912:546). Measurements of both its tarsus (176.5 mm) and culmen (137 mm) far exceed the respective cut-offs of 161 mm and 134 mm given for fannini by Vennesland and Butler (2011). Measurements of an unsexed bird from Cape Flattery, central-western Washington (no date given), fall within the mid-range given for female treganzai (except the tail which was slightly shorter), and within the upper half of the range of female fannini (Oberholser 1912), suggesting it could be from either subspecies. Thus, it appears that neither Washington specimen is clearly fannini, and both specimens from this transitional zone could more likely be grouped with the subspecies occurring to the south. Despite this, Oberholser’s (1912) extension of the range of fannini on the basis of these two specimens was later adopted by some authors (see below).

The 1957 edition of the American Ornithologists Union (AOU) checklist was the last one to consider subspecies of North American birds (American Ornithologists’ Union 1957). It indicated that fannini bred along the Pacific coast from southeastern Alaska (Yakutat Bay) south to Washington, approximately the same range identified by Oberholser (1912). It considered fannini to be “mainly resident, wanders to Cook Inlet, Alaska [presumably the record noted by Oberholser 1912], and the interior of central and southern British Columbia (Bulkley Lake).” (American Ornithologists’ Union 1957).

Payne (1979) gave the range of fannini as the Pacific coast of North America, from southeastern Alaska (Yakutat Bay) south through Haida Gwaii and coastal British Columbia to coastal Washington, similar to the range identified by Oberholser (1912) and the American Ornithologists’ Union (1957). He noted that it wintered within the breeding range and “wanders inland” (Payne 1979), but did not describe its morphology or plumage characteristics.

Dickerman (2004a,b) undertook a comprehensive study of the characteristics and distribution of fannini, examining 26 birds from across North America for plumage coloration and, for mensural data, 14 birds from Haida Gwaii north into Alaska, 52 from southwestern British Columbia and Washington, and 61 from California (which he referred to as the hyperonca type, although he ultimately considered these birds to be within herodias). He grouped the grey forms of A. herodias into just three subspecies overall: the moderately grey herodias, paler wardi, and darker fannini (Dickerman 2004a). He advised caution when interpreting plumage colour, showing that some of the dark feather colour noted by Chapman (1901) for the fannini type specimen came from the washing of specimens that removed greyish powder-down from the plumage surface (Dickerman 2004b). After accounting for this possible effect, he concluded that there was a noticeable colour change north of Vancouver Island, with birds from Haida Gwaii north being uniformly dark in comparison with those farther south, although this was likely based on a relatively small sample. He showed that both tarsus and culmen measurements increased clinally along the Pacific coast from southeastern Alaska and Haida Gwaii, through an intermediate population in southern British Colombia and Washington, to California,^{Footnote 1} and that fannini birds from Haida Gwaii north had the shortest tarsi and culmens of any Great Blue Herons, and were significantly smaller than the hyperonca type in California (Dickerman 2004a,b).

Dickerman (2004b) also noted that adult Great Blue Herons from southwestern British Columbia (including Vancouver Island) and from Washington were intermediate in size and colour between the dark fannini and paler hyperonca types, suggesting a broad transitional mixing zone of clinal change. As a consequence of his investigations of morphometrics and plumage colour, Dickerman (2004a,b) recommended that the range of fannini be restricted to Haida Gwaii and southeastern Alaska north to Prince William Sound.

Both previous COSEWIC status reports (Butler 1997; COSEWIC 2008) considered the range of fannini, and thus the DU based on this subspecies, to include much of coastal mainland British Columbia west of the Coast Mountains (described as that portion of the Coastal Western Hemlock and Coastal Douglas-fir biogeoclimatic zones within 10 km of the coast or large river systems), and adjacent coastal and offshore islands, including Haida Gwaii and Vancouver Island. This range was based largely on Payne (1979), and was subsequently used in the Species at Risk Act management plan for fannini (Environment and Climate Change Canada 2020). COSEWIC (2008) briefly considered whether fannini should be considered as restricted to Haida Gwaii, the adjacent northern coast of British Columbia, and southeastern Alaska, as recommended by Dickerman (2004b), but used the same range as Butler (1997), based on the distribution given by the American Ornithologists’ Union (1957) and Payne (1979). However, it noted that genetic evidence would assist in clarifying the degree of separation of subspecies and in identifying appropriate geographical boundaries (COSEWIC 2008). Genetic information now available (for example, Cheek et al. 2018) appears to provide support for the more restricted range of fannini proposed by Dickerman (2004a).

Vennesland and Butler (2011) considered fannini to be resident from southwestern Alaska (Prince William Sound) south to Haida Gwaii. They include birds resident in southwestern British Columbia, including Vancouver Island, as well as those in western Washington, which they indicated were intermediate in colour and size between fannini and wardi to the south, based on Dickerman (2004a,b), who considered these southern birds to be herodias. They indicated that the taxonomic status of the birds in mainland British Columbia north of Vancouver was unclear (Vennesland and Butler 2011). They described adult fannini as being dark grey relative to the subspecies farther south on the Pacific coast, with a shorter culmen and tarsus (see above; Dickerman 2004a,b), but with similar wing and tail lengths (referring to mensural data in Oberholser 1912 and Dickerman 2004a; Vennesland and Butler 2011).

In summary, there is some evidence that Great Blue Herons from Haida Gwaii and the adjacent northern coast of British Columbia are darker grey than those farther south on the Pacific coast of British Columbia and northwestern United States, with a shorter exposed culmen and tarsus (summarized in Vennesland and Butler 2011). Great Blue Herons from southwestern British Columbia, including Vancouver Island, are intermediate in both size and colour between the darker birds to the north and paler herons to the south, indicating a broad transitional mixing zone (Vennesland and Butler 2011). Although birds from Haida Gwaii north are darker (Dickerman 2004b), both tarsus and culmen measurements increase clinally from Alaska south through southern coastal British Columbia (Dickerman 2004a,b; Vennesland and Butler 2011), with no clear boundary in terms of size between birds from Haida Gwaii and those farther south. Although further consideration of the most appropriate delineation of the range of the Great Blue Heron fannini subspecies in Canada would be useful, such a study is outside the remit of this report.

Population genetics

Cheek et al. (2018) considered genetic differences among Great Blue Herons on the northwest Pacific coast, focusing on the endemism of birds from Haida Gwaii. They examined the divergence in the mitochondrial gene for NADH dehydrogenase subunit 2 (ND2), a marker used in other studies of avian regional endemism (for example, Drovetski et al. 2004). Although ND2 is only a single genetic marker, mitochondrial DNA (mtDNA) divergence has been shown to be a good general predictor of differentiation in the nuclear genome among and within species (for example, Figure S2 in Toews et al. 2016), aside from uncommon instances of mitochondrial introgression (Toews and Brelsford 2012). Cheek et al. (2018) analyzed 36 samples from nine sites in western North America, including 22 considered fannini (most from Haida Gwaii [12] and Alaska [7], but also including three from Vancouver Island) and 14 considered herodias and wardi, chosen to maximize geographic coverage. Note that four of the specimens they considered to be herodias were from extreme northwestern Washington, well within the clinal mixing zone between fannini and herodias farther south (see Assessment Against Designatable Unit criteria below).

They found “remarkably low genetic diversity” in the samples of A. herodias, no significant population divergence in the sequence or haplotype frequencies of ND2 between herodias and fannini, and no unique haplotypes in fannini (Cheek et al. 2018:55). They concluded that, in contrast to most other regional endemic bird species that persisted through at least one Ice Age in an unglaciated refugium, fannini has likely arisen relatively recently, with its possible adaptation to local environments paralleling that of the region’s older endemics. They concluded that fannini is an endemic population that has undergone sufficient phenotypic differentiation from the widespread continental population (darker coloration) to be recognized as a subspecies (following for example, Chapman 1901; Dickerman 2004a,b), but without significant population divergence from herodias at the genetic level (Cheek et al. 2018).

McGuire et al. (2019) analyzed genetic data for Great White and Great Blue Herons (four named subspecies) using 13 nuclear microsatellite DNA makers. Eleven birds were from northwestern Washington, in the area that Dickerman (2004b) considered the mixing zone south of the range of fannini, but that previous COSEWIC reports had considered within the range of fannini (COSEWIC 2008; see Assessment against Designatable Unit criteria below). Note that three of these samples are mapped in Figure 1 in McGuire et al. (2019) as occurring on Vancouver Island, but the authors’ Table S2 confirms that none were from Canada (Taylor pers. comm. 2022). Since McGuire et al. (2019) focused on genetic differentiation in herons in Florida, that paper is used here only to show general patterns of population genetics in the species. However, since these authors’ analyses used the Bayesian population assignment approach implemented in STRUCTURE without a-priori population information, their results can indirectly inform the present assessment of a possible Great Blue Heron DU in the Pacific Northwest (McGuire et al. 2019).

The STRUCTURE analysis conducted by McGuire et al. (2019) indicated that the best number of genetic clusters (K) across the species’ range was two, with one cluster consisting of fannini, herodias, and wardi, suggesting high levels of continent-wide gene flow among these subspecies. Clustering of fannini from other birds occurred when K = 5-7, providing some evidence of limited hierarchical clustering (Taylor pers. comm. 2022). Isolation-by-distance analysis across the entire Great Blue Heron range indicates that most differentiation (as estimated using F_ST) was attributable to geographic separation (McGuire et al. 2019). As no birds were sampled between the Pacific coast and the vicinity of the Great Lakes (herodias), the significant F_ST value (0.083) differentiating these two groups is less indicative of the groups being two discrete units than the result of sampling the extreme ends of a range (Taylor pers. comm. 2022). This is consistent with a stepping-stone model of gene flow that leads to isolation by distance, where an increase in genetic differentiation is associated with greater geographical separation (Taylor pers. comm. 2022).

In summary, the mitochondrial sequence analyzed by Cheek et al. (2018) showed no significant genetic divergence between herodias and fannini. Although genetic assessments by McGuire et al. (2019) using microsatellites showed very low, but detectable, genetic differentiation between birds that they considered fannini from northwestern Washington and other subspecies, they concluded that such differentiation among Great Blue Herons in North America reflected isolation by distance.

Migratory behaviour and post-fledging movements

COSEWIC (2008) indicates that fannini is largely resident in coastal British Columbia with a non-migratory life history. However, it may undertake local post-breeding movements and appears to leave some areas during the non-breeding season (Oberholser 1912; Figure 1), and occasionally wanders to the interior of central and southern British Columbia (American Ornithologists’ Union 1957; Payne 1979). The herodias subspecies is generally migratory across Canada, with the exception of some warmer areas of extreme southern Ontario and southern interior British Columbia (Figure 1), and is migratory in parts of the northern United States but resident in others (Vennesland and Butler 2011; Figure 1). Some herodias birds have long been known to remain in British Columbia’s Okanagan Valley well into the winter, and were considered a fairly common year-round resident there by the 1980s (Cannings et al. 1987). Van Damme (2020) indicates that the Great Blue Heron (presumed herodias) is present each winter in variable numbers in specific areas of the Creston Valley of southern British Columbia. Together, these observations indicate that Great Blue Herons of either subspecies may take advantage of mild conditions to overwinter, and that this behaviour is not unique to fannini and may be a plastic response to mild environmental conditions.

Records of Great Blue Herons banded as chicks throughout North America, held by the US Geological Survey (USGS) Bird Banding Laboratory (2022), were recently reviewed to provide an independent way to consider the extent to which mountain ranges may represent a barrier to movements and dispersal. Although there are few sites where birds considered fannini are banded, young herons banded in the Vancouver area were recovered near Kamloops, in the southern Okanagan Valley, and in northwestern Washington, and birds banded in central Washington were recovered near Kelowna, British Columbia, and across western North America (USGS Bird Banding Laboratory 2022). This indicates that young Great Blue Herons, including those considered fannini, can readily disperse across considerable distances, including between areas separated by mountainous regions, enabling possible genetic interchange. That dispersal is consistent with a stepping-stone model of gene flow, with birds tending to disperse to neighbouring areas.

Assessment against Designatable Unit criteria

The available evidence related to plumage characteristics, morphology, geographic disjunction, migratory behaviour, and population genetics is assessed here against current criteria for discreteness and evolutionary significance (COSEWIC 2020), to consider whether the subspecies fannini meets these criteria for a valid DU.

In this evaluation, it is important to consider whether the range of the DU being evaluated as subspecies fannini is that described in previous COSEWIC status reports (Butler 1997; COSEWIC 2008), following Oberholser (1912), American Ornithologists’ Union (1957), and Payne (1979), or is further restricted based on more recent mensural and genetic data, as per Dickerman (2004a,b) and Cheek et al. (2018). Although the latter restricted range description better reflects recent assessments of morphology, plumage, and genetics, to date, COSEWIC has considered the broad range. As a consequence, this report will evaluate the available evidence for discreteness and significance for both of these DU range scenarios, described as follows:

• restricted DU range scenario: Great Blue Herons in a range within Canada restricted to Haida Gwaii and the northern Pacific coast of British Columbia, as described as fannini by Dickerman (2004a,b), with the coastal areas farther south in British Columbia, including Vancouver Island, considered to be a broad intergrade zone between subspecies, and
• broad DU range scenario: Great Blue Herons in a range within Canada that includes Haida Gwaii, Vancouver Island, and the coastal islands and coastal mainland of British Columbia, as described as fannini by COSEWIC (2008)

Discreteness

Criterion D1. Evidence of heritable traits or markers that clearly distinguish fannini from herodias (for example, evidence from genetic markers or heritable morphology, behaviour, life history, phenology, migration routes, vocal dialects, etc.), indicating limited transmission of this heritable information to and between other DUs (COSEWIC 2020)

• fannini from Haida Gwaii north (restricted range) have darker plumage on the neck and upper parts than herodias, with a shorter culmen and tarsus, similar wing lengths, and longer tails (Dickerman 2004b; Vennesland and Butler 2011). These traits may be an associated adaptation to fannini’s largely resident status and winter feeding habits in coastal and open inland habitats, and its tendency to fish from rocks more than longer-legged subspecies (Dickerman 2004a). Birds occurring south of Haida Gwaii (broad range) are intermediate in size and colour between birds to the north and south (Dickerman 2004b; Vennesland and Butler 2011). While these characteristics may be heritable, a clear clinal change in culmen and tarsus measurements (Dickerman 2004b) indicates that the transmission of this information is not limited in either the restricted or broad-range scenarios (Cheek et al. 2018)
• fannini is largely non-migratory, with most remaining in southern British Columbia year-round (COSEWIC 2008; Birds Canada 2020), although some individuals in both the restricted- and broad-range scenarios appear to leave breeding areas in winter (Figure 1). Non-migratory behaviour presumably enables birds to avoid costs associated with migration, and to take advantage of the relatively mild temperatures and open shorelines in coastal British Columbia in winter. Wide-ranging herodias is generally migratory in most of Canada, although some birds overwinter in southern Ontario (Figure 1; Vennesland and Butler 2011), and in valleys in southern interior British Columbia (for example, Cannings et al. 1987; Van Damme 2020). Migratory tendency has been linked to genetic differences in other avian taxa (Delmore and Liedvogel 2020). However, as some individuals of both subspecies overwinter in southern British Columbia, migratory tendency is likely not a distinguishing characteristic between Great Blue Heron subspecies, but a response to local environmental conditions
• Using mtDNA population genetics analysis, Cheek et al. (2018) found no significant population divergence between herodias (or other subspecies) and fannini, considering either the restricted- or broad-range scenarios, with no unique haplotypes or significant genetic divergence in their frequencies. McGuire et al. (2019) showed very low, but detectable, genetic differentiation between fannini (n = 11, broad-range scenario only) and the other subspecies, consistent with some limitation on gene flow. However, given that the sample size for fannini was small, sampling sites were several thousands of kilometres apart, and there was a strong pattern of isolation by distance, robust conclusions on the discreteness of fannini cannot be drawn from these microsatellite data

In summary, there is no direct evidence regarding the heritability of observed phenotypic differences between fannini and herodias in plumage, morphology, or migration behaviour. The lack of evidence of genetic differentiation in mtDNA between these subspecies (Cheek et al. 2018) indicates that the transmission of heritable information is not limited in either the restricted- or broad-range scenarios. The evidence from nuclear microsatellites from McGuire et al. (2019) does show low, but detectable, differentiation between fannini (broad range, from Washington) and other subspecies (herodias and wardi), although this is interpreted by McGuire et al. (2019) as likely reflecting isolation by distance. Taken together, this evidence suggests that it is possible, although unlikely, that criterion D1 applies for the broad-range scenario, although not for the restricted range scenario.

Criterion D2. Natural geographic disjunction between these DUs such that the transmission of information (for example, individuals, seeds, gametes) between these "range portions" has been severely limited for an extended time and is not likely in the foreseeable future. “Extended time” is intended to mean that sufficient time has passed that either natural selection or genetic drift are likely to have produced discrete units, given the specific biology of the taxon (COSEWIC 2020).

• There is little evidence of the effectiveness of the Coast Mountains as a reproductive barrier to the east, and there is likely occasional interchange of individuals in southern British Columbia where major river systems cross the Coast Mountain range (Meidinger and Pojar 1991), as evidenced by occasional non-migratory, seasonal movements of birds considered to be fannini (American Ornithologists’ Union 1957; Payne 1979). It is unclear whether these movements were of birds from the restricted or broad range, although the effectiveness of a Coast Mountain range barrier is likely greater for birds from Haida Gwaii north (restricted range scenario)
• Bird-banding records provide an independent way of assessing whether mountain ranges represent a barrier to heron dispersal. Great Blue Herons banded as chicks in the Vancouver area have been recovered in south-central British Columbia and northwestern Washington, and those banded in central Washington have been recovered in south-central British Columbia and across western North America (USGS Bird Banding Laboratory 2022), indicating that young Great Blue Herons, including fannini (broad-range scenario), disperse between areas separated by mountainous regions, enabling possible genetic interchange
• Tarsus and culmen length of coastal Great Blue Herons increase clinally along the Pacific coast from southeastern Alaska through British Columbia to California (Dickerman 2004a,b), and birds resident in southwestern British Columbia, including Vancouver Island (broad-range scenario), are intermediate in size and colour between birds to the north and south (Dickerman 2004a, b; Vennesland and Butler 2011). This indicates that there is no effective geographic disjunction from north to south between fannini and adjacent subspecies, whether considering the restricted- or broad-range scenarios
• Cheek et al. (2018) showed no differentiation based on mitochondrial DNA between fannini (either restricted- or broad-range scenarios) and herodias, indicating that the movement of individuals or genetic information between them has not been severely limited for an extended time

Thus, the lack of effective geographic disjunction (especially for birds in the broad-range scenario), the strictly clinal changes in morphology (both range scenarios), and the lack of genetic mitochondrial differentiation (both range scenarios) all indicate that the transmission of information between fannini from Haida Gwaii north (restricted range scenario), fannini south of Haida Gwaii (broad-range scenario), and herodias farther south and east, has not been severely limited for an extended time. Criterion D2 therefore does not apply.

Evolutionary significance

Current COSEWIC guidelines for the recognition of DUs (COSEWIC 2020) indicate that if a possible DU is found to be discrete, its evolutionary significance can be assessed. As there is a slight possibility that criterion D1 for discreteness may apply to fannini (broad-range scenario), significance is assessed here. Note that the microsatellite data from McGuire et al. (2019) cannot be used to assess evolutionary significance, because these are neutral markers that do not affect adaptive traits, and they evolve too quickly to assess origins in separate refugia.

Criterion S1. Direct evidence or strong inference that the putative DU has been on an independent evolutionary trajectory for an evolutionarily significant period, usually intraspecific phylogenetic divergence indicating origins in separate Pleistocene refugia (COSEWIC 2020)

• Some evidence consistent with an independent evolutionary trajectory is provided by measurable plumage and morphological differences between fannini from Haida Gwaii and north (restricted range only) and birds farther south assigned to herodias, although many differences vary clinally (Dickerman 2004a; considered in D1 above)
• However, the mtDNA genetic analyses conducted by Cheek et al. (2018) show no significant sequence divergence between herodias and fannini (either restricted or broad range), and indicate that fannini has arisen relatively recently compared with other regional endemics, and that differences are of post-Pleistocene origin

As there is no evidence or strong inference that fannini has been on an independent evolutionary trajectory for an evolutionarily significant period, under either the restricted- or broad-range scenarios, criterion S1 does not apply.

Criterion S2. Direct evidence or strong inference that the putative DU possesses adaptive, heritable traits that cannot be practically reconstituted if lost: for example, persistence of the discrete, putative DU in an ecological setting where a selective regime is likely to have given rise to DU-wide local adaptations that could not be reconstituted (COSEWIC 2020)

• It can be inferred that birds assigned to fannini occur in a coastal ecological setting with relatively wet, mild winters, where this selective regime could have given rise to local adaptations (for example, in plumage and morphology within the restricted range, and predominantly non-migratory behaviour in both restricted- and broad-range scenarios; COSEWIC 2008)
• However, as morphological differences vary clinally to the south through both the restricted and broad ranges (Dickerson 2004b; Vennesland and Butler 2011), there is no direct evidence of a genetic basis for these differences (Cheek et al. 2018), and there is no evidence that they could not be reconstituted if lost. For example, non-migratory behaviour is observed in coastal and southern interior portions of British Columbia (Figure 1; Cannings et al. 1987; Vennesland and Butler 2011; Van Damme 2020), where it appears to be related to mild environmental conditions and the presence of open water in winter, suggesting a plastic response to environmental conditions rather than a heritable trait that could not be reconstituted if lost

As there is no evidence that any differences in size and plumage coloration are local adaptations in fannini that could not be practically reconstituted if lost, whether considering the restricted- or broad-range scenarios, criterion S2 does not apply.

Conclusion

Although it is possible that the Great Blue Heron fannini subspecies may meet one current COSEWIC criterion for discreteness under the broad-range scenario only, there is no evidence in support of either criteria for evolutionary significance, under either the restricted- or broad-range scenario. As a consequence, the null hypothesis that there is only one Great Blue Heron DU in Canada is not rejected, and the former Great Blue Heron fannini subspecies (Ardea herodias fannini) DU is not considered to be valid under current COSEWIC guidelines, whether described using either the restricted- or broad-range scenario. It is therefore not eligible for COSEWIC status assessment.

Range

Addendum 7: Change in Extent of Occurrence (EOO): Not applicable

Addendum 8: Change in Index of Area of Occupancy (IAO) : Not applicable

Addendum 9: Change in number of known or inferred current locations^{Footnote 2}: Not applicable

Addendum 10: Significant new survey information: Not applicable

Explanation: Not applicable, as this subspecies is considered ineligible for assessment

Population information

Addendum 11: Change in number of mature individuals: Not applicable

Addendum 12: Change in population trend: Not applicable

Addendum 13: Change in severity of population fragmentation: Not applicable

Addendum 14: Change in trend in area and/or quality of habitat: Not applicable

Addendum 15: Significant new survey information: Not applicable

Explanation: Not applicable, as this subspecies is considered ineligible for assessment

Threats

Addendum 16: Change in nature and/or severity of threats: Not applicable

Explanation: Not applicable, as this subspecies is considered ineligible for assessment

Protection

Addendum 17: Change in effective protection: Not applicable

Explanation: Not applicable, as this subspecies is considered ineligible for assessment

Rescue effect

Addendum 18:

Change in evidence of rescue effect: Not applicable

Explanation: Not applicable, as this subspecies is considered ineligible for assessment

Quantitative analysis

Addendum 19: Not applicable

Change in estimated probability of extirpation: Not applicable

Details: Not applicable, as this subspecies is considered ineligible for assessment

Summary and additional considerations

The Great Blue Heron fannini subspecies is considered to be ineligible for status assessment, whether evaluated using either the restricted- or broad-range scenario, as it does not meet the criteria for both discreteness and evolutionary significance as required under the revised 2020 COSEWIC guidelines for recognizing designatable units based on taxonomic subspecies (COSEWIC 2020), and is thus not a valid DU.

Acknowledgements

Many thanks to Ross Vennesland, the writer of the 2022 draft update status report for the Great Blue Heron fannini subspecies, and to those members of the COSEWIC Birds SSC who reviewed the draft status report and addendum, including Louise Blight, Elsie Krebs, Jean-Pierre Savard, and especially Co-chair Marcel Gahbauer. Thanks to the past and current chairs of the COSEWIC DU Working Group, Christina Davy and Arne Mooers, for their guidance in interpreting the current DU guidelines. The considered discussion among COSEWIC members at the May 2022 species assessment meeting, including David Fraser, Purnima Govindarajulu, Dwayne Lepitzki, Arne Mooers, John Reynolds, Gina Schalk, and Sabrina Taylor, is appreciated. Many thanks to Sabrina Taylor for her many insightful contributions to the writing of this addendum. Thanks to those who reviewed the first draft of this report on behalf of relevant jurisdictions, including Blythe Beynon, Rob Butler, Syd Cannings, Jenna Cragg, Leah de Forest, Kimberly Dohms, David Fraser, Purnima Govindarajulu, Eric Gross, Nathan Hentze, and Ross Vennesland. In addition, thanks to Ashley Long of Louisiana State University for mapping Great Blue Heron banding recoveries, and key members of the COSEWIC Secretariat team for guidance on procedures and formatting, including Marie-France Noël, Tanya Pulfer, Karen Timm, and Lisa Twolan.

Authorities contacted

• Davy, Christina. Assistant Professor, Department of Biology, Carleton University, Ottawa, Ontario, and former COSEWIC Member for Ontario
• Govindarajulu, Purnima. Unit Head, Species Conservation Science Unit, British Columbia Ministry of Environment and Climate Change Strategy, Victoria, British Columbia, and COSEWIC Member for British Columbia
• Hentze, Nathan. CDC Zoologist, British Columbia Conservation Data Centre, British Columbia Ministry of Land, Water and Resource Stewardship, Victoria, British Columbia
• Mooers, Arne. Professor, Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, and COSEWIC Non-government Science Member
• Taylor, Sabrina. Weaver Brothers Distinguished Professor, School of Renewable Natural Resources, Louisiana State University, Baton Rouge, Louisiana, and COSEWIC Non-government Science Member
• Vennesland, Ross. Senior Species at Risk Biologist, Species at Risk Recovery Unit, Canadian Wildlife Service - Pacific Region, Environment and Climate Change Canada, Delta, British Columbia

Information sources

American Ornithologists’ Union. 1957. Check-list of North American birds. 5th edition. American Ornithologists’ Union, Baltimore, Maryland. 691 pp.

Birds Canada. 2020. British Columbia Coastal Waterbird Survey. Data accessed from NatureCounts, a node of the Avian Knowledge Network, Birds Canada. Website: http://www.naturecounts.ca/ [accessed May 2022].

Butler, R.W. 1997. COSEWIC status report on the Pacific Great Blue Heron Ardea herodias fannini in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa. ii + 9 pp.

Cannings, R.A., R.J. Cannings, and S.G. Cannings. 1987. Birds of the Okanagan Valley, British Columbia. Royal British Columbia Museum, Victoria, British Columbia. 420 pp.

Chapman, F.M. 1901. A new race of the Great Blue Heron, with remarks on the status and range of Ardea wardi. Bulletin American Museum of Natural History 14:87-90.

Cheek, R.G., K.K. Campbell, and K. Winker. 2018. Mitochondrial DNA suggests recent origins of subspecies of the Sharp-Shinned Hawk and Great Blue Heron endemic to coastal British Columbia and southeast Alaska. Western Birds 49:47-61.

COSEWIC. 2008. COSEWIC assessment and update status report on the Great Blue Heron fannini subspecies Ardea herodias fannini in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa. vii + 39 pp. Website: https://species-registry.canada.ca/index-en.html#/documents/1615 [accessed May 2022].

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

Delmore, K.E., and M. Liedvogel. 2020. Avian population genomics taking off: Latest findings and future prospects. Statistical Population Genomics, pp. 413-433, in J.Y. Dutheil (ed.), Statistical Population Genomics, Methods in Molecular Biology: 2090. https://doi.org/10.1007/978-1-0716-0199-0_17.

Dickerman, R.W. 2004a. A review of the North American subspecies of the Great Blue Heron (Ardea herodias). Proceedings of the Biological Society of Washington 117:242-250.

Dickerman, R.W. 2004b. Characteristics and distribution of Ardea herodias fannini with comments on the effect of washing on the holotype. Northwestern Naturalist 85:130-133.

Drovetski, S.V., R.M. Zink, S. Rohwer, I.V. Fadeev, E.V. Nesterov, I. Karagodin, E.A. Koblik, and Y.A. Red'kin. 2004. Complex biogeographic history of a Holarctic passerine. Proceedings of the Royal Society B (Biological Sciences) 271. https://doi.org/10.1098/rspb.2003.2638.

Environment and Climate Change Canada. 2020. Management Plan for the Great Blue Heron fannini subspecies (Ardea herodias fannini) in Canada. Species at Risk Act Management Plan Series. Environment and Climate Change Canada, Ottawa. iii + 26 pp. Website: https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/management-plans/great-blue-heron-fannini-2020.html [accessed May 2022].

Fink, D., T. Auer, A. Johnston, M. Strimas-Mackey, O. Robinson, S. Ligocki, W. Hochachka, L. Jaromczyk, C. Wood, I. Davies, M. Iliff, L. Seitz. 2021. eBird status and trends, data version: 2020; released: 2021. Cornell Lab of Ornithology, Ithaca, New York. https://doi.org/10.2173/ebirdst.2020.

McGuire, H.L., S.S. Taylor, and F.H. Sheldon. 2019. Evaluating the taxonomic status of the Great White Heron (Ardea herodias occidentalis) using morphological, behavioral and genetic evidence. The Auk Ornithological Advances 136:1-18.

Meidinger, D., and J. Pojar. 1991. Ecosystems of British Columbia. British Columbia Ministry of Forestry Special Report Series No. 6, Victoria, British Columbia, 330 pp. Website: https://www.for.gov.bc.ca/hfd/pubs/Docs/Srs/Srs06.htm [accessed May 2022].

Oberholser, H.C. 1912. A revision of the forms of the Great Blue Heron (Ardea herodias Linnaeus). Proceedings of the U.S. National Museum 43:531-559. Website: https://www.biodiversitylibrary.org/page/7723515#page/639/mode/1up [accessed September 2022].

Payne, R.B. 1979. Ardeidae. Pp. 193-244 in E. Mayr and G.W. Cottrell (eds.). Checklist of Birds of the World. Museum of Comparative Zoology, Cambridge, Massachusetts.

Taylor, S.S., pers. comm. 2022. Email correspondence to R.D. Elliot. May 2022. Weaver Brothers Distinguished Professor, School of Renewable Natural Resources, Louisiana State University, Baton Rouge, Louisiana.

Toews, D.P.L., and A. Brelsford. 2012. The biogeography of mitochondrial and nuclear discordance in animals. Molecular Ecology 21:3907-30. https://doi.org/10.1111/j.1365-294X.2012.05664.x

Toews, D.P.L., S.A. Taylor, R. Vallender, A. Brelsford, B.G. Butcher, P.W. Messer, and I.J. Lovette. 2016. Plumage genes and little else distinguish the genomes of hybridizing warblers. Current Biology 26:2313-2318. https://doi.org/10.1016/j.cub.2016.06.034.

USGS Bird Banding Laboratory. 2022. Band recovery data for Great Blue Herons banded and recovered in North America. Website: https://www.pwrc.usgs.gov/BBL/Bander_Portal/login/bbl_data_request_summary.php [accessed July 2022].

Van Damme, L. 2020. A passion for birds – their life in the Creston Valley. Self-published. Creston, British Columbia. 532 pp.

Vennesland, R.G., and R.W. Butler. 2011. Great Blue Heron (Ardea herodias), version 2.0. In A.F. Poole (Ed.). The Birds of North America. Cornell Lab of Ornithology, Ithaca, New York. Website: https://doi.org/10.2173/bna.25 [accessed May 2022].

Vennesland, R. G., and R. W. Butler. 2020. Great Blue Heron (Ardea herodias), version 1.0. In A.F. Poole (Ed.). Birds of the World. Cornell Lab of Ornithology, Ithaca, New York. Website: https://doi.org/10.2173/bow.grbher3.01 [accessed May 2022].

Writers of the addendum

Dr. Richard D. Elliot has served as a member of the Birds Specialist Sub-committee (SSC) since January 2015, and as Co-chair of the SSC and Member of COSEWIC since January 2017. He received his MSc from Acadia University and his PhD from the University of Aberdeen in Scotland. He retired in 2015 from a career with Environment Canada, as a migratory birds and species-at-risk biologist and research manager with the Canadian Wildlife Service, and as National Director of Wildlife Research with the Wildlife and Landscape Science Directorate. As SSC Co-chair, he has overseen the preparation of seventeen COSEWIC status reports, and led in the writing of the 2019 Designatable Unit report for Red Knot (Calidris canutus) and the 2022 Designatable Unit report for Northern Goshawk (Accipiter gentilis).

Dr. David P.L. Toews has served as the population genetics specialist member of the Birds Specialist Sub-committee since January 2018. He is an assistant professor in the Department of Biology at Pennsylvania State University. He received his MSc and PhD from the Department of Zoology at the University of British Columbia, and briefly worked with the Species at Risk recovery planning group with the Canadian Wildlife Service in Delta, British Columbia. His research is focused on evolutionary biology, genomics, and molecular ecology in avian systems, often combining genomic data with other phenotypic, behavioural, and biogeographic information to make inferences about evolutionary processes. He co-wrote the 2022 Designatable Unit report for Northern Goshawk.

Technical summary

Ardea herodias fannini

Great Blue Heron fannini subspecies

Grand héron de la sous-espèce fannini

Range of occurrence in Canada (province/territory/ocean): British Columbia

Demographic information

Generation time (usually average age of parents in the population; indicate if another method of estimating generation time indicated in the IUCN guidelines (2011) is being used):

Not applicable

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

Not applicable

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

Not applicable

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

Not applicable

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

Not applicable

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

Not applicable

Are the causes of the decline a. clearly reversible and b. understood and c. ceased?

Not applicable

Are there extreme fluctuations in number of mature individuals?

Not applicable

Extent and occupancy information

Estimated extent of occurrence (EOO):

Not applicable

Index of area of occupancy (IAO) (Always report 2x2 grid value):

Not applicable

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

Not applicable

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

Not applicable

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

Not applicable

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

Not applicable

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

Not applicable

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

Not applicable

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

Not applicable

Are there extreme fluctuations in number of subpopulations?

Not applicable

Are there extreme fluctuations in number of “locations”^*?

Not applicable

Are there extreme fluctuations in extent of occurrence?

Not applicable

Are there extreme fluctuations in index of area of occupancy?

Not applicable

^* See COSEWIC definitions and abbreviations on website for more information on this term.

Number of mature individuals (in each subpopulation)

Subpopulations (give plausible ranges): Not applicable

N mature individuals total: Not applicable

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]?

Not applicable

Threats (direct, from highest impact to least, as per IUCN threat calculator)

Was a threats calculator completed for this species?

Not applicable

What additional limiting factors are relevant?

Not applicable

Rescue effect (immigration from outside Canada)

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

Not applicable

Is immigration known or possible?

Not applicable

Would immigrants be adapted to survive in Canada?

Not applicable

Is there sufficient habitat for immigrants in Canada?

Not applicable

Are conditions deteriorating in Canada?⁺

Not applicable

Are conditions for the source (i.e., outside) population deteriorating?⁺

Not applicable

Is the Canadian population considered to be a sink?⁺

Not applicable

Is rescue from outside populations likely?

Not applicable

⁺ See Table 3 (Guidelines for modifying status assessment based on rescue effect).

Data sensitive species

Is this a data sensitive species? Not applicable

Status history

COSEWIC: Designated Special Concern in April 1997. Status re-examined and confirmed in April 2008.

Status and reasons for designation:

Status: Not applicable

Alpha-numeric codes: Not applicable

Reasons for designation (2022): Status is not assigned. This population is no longer a valid Designatable Unit, as it does not meet the 2020 revised COSEWIC criteria for discreteness and evolutionary significance and is, therefore, not eligible for COSEWIC status assessment.

Applicability of criteria

Criterion A (Decline in total number of mature individuals): Not applicable

Criterion B (Small distribution range and decline or fluctuation): Not applicable

Criterion C (Small and declining number of mature individuals): Not applicable

Criterion D (Very small or restricted population): Not applicable

Criterion E (Quantitative analysis): Not applicable

Figure 1. eBird range map of Great Blue Heron, showing areas where the species is estimated to occur within at least one week within each season, based on sightings submitted by amateur birders through the year. Occurrence is shown as year-round (purple), breeding season (weeks beginning 10 May to 28 June; red), non-breeding season (28 December to 25 January; blue), and pre-breeding and post-breeding migratory seasons (1 February to 3 May; 6 July to 21 December; yellow) (from Fink et al. 2021).

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 (2022)

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.