A New North American Larus? - The "Giant" Herring Gull

"Birders care only for more lifers. Taxonomists want a cheap honorific. Nobody touches the splits that actually make sense."

This grim pseudo-haiku comes from my late friend Jim Pranty, long-time habitué of Midwestern reservoirs and reluctant witness to ornithology's ever-shifting taxonomic circus. Ad nauseum he preached that the science of naming birds too often resembles a game of musical chairs, where the prizes go to the most flamboyant or conveniently ambiguous forms, while the quietly distinct taxa languish ignored. It is from this vantage that I offer the following account, compiled over decades of dedicated fieldwork and intensive study spanning two continents, with the goal of revealing an astounding assortment of previously undocumented forms found amongst what armchair checklist committees, in their infinite wisdom, have long penned a single, monotypic species. 

Domineering titans of North Pacific coastlines, a cryptic diversity within the Glaucenscens Complex (GC) has long been recognized among a minute handful of American gull-watchers. Unfortunately, this rare acknowledgement is oft-given with the apologetic air of one admitting to a superstition, lest their views offend the all-knowing arbiters of taxonomy. To most, GWG are a vague gray smear to be lumped wholesale for convenience's (or simplicity's) sake, painted in the broadest of brushes and preserved in the embalming fluid of monotypy.  

Fig. 1: the carefully-mapped living archipelago of GWG; 23 distinct forms in 7 groups stretching from Puget Sound to Kamchatka

Through 3 decades of field observation, sampling of morphometric and plumage traits, and comparison of museum specimens, it is apparent that the long-accepted (and scantly-defended) consideration of GWG as monotypic is untenable. Accumulated evidence instead indicates a geographically structured complex comprising no fewer than 23 diagnosable subspecies, organized into 7 coherent regional groups and expressing consistent variation in mantle shade, wingtip pigmentation, bare parts colouration (especially orbital ring), bill proportions, and overall body size. These groups and the subspecies they contain are listed below, along with details pertaining to their breeding distributions, physical characteristics aiding identification, and photo media from the Ebird web site. Where relevant, I also make note genetic signals, though in most cases the weight of observable differences renders molecular corroboration (which is often inaccurate) nearly superfluous. "When genetic assays are held in higher esteem than plainly visible traits, all is lost (see the AOU's current battue of a checklist!)"... this again comes, exasperatedly, from JP. 

Pugetensis 

-L. g. prantyi - coastal northwest Oregon through coastal Washington
-L. g. pugetensis - Puget Sound, north to southern edge of Juan de Fuca Strait
-L. g. intermedia - cryptic, primarily San Juan Islands and perhaps elsewhere in Juan de Fuca Strait
-L. g. vancouverensis - coastal Vancouver Island and mainland British Columbia, north through Georgia and Johnstone Straits

This distinctive assemblage represents the southernmost members of the GC, as well as the darkest-plumaged and heaviest-proportioned (often falsely labelled as L. occidentalis x GWG hybrids). See Bergmann's Rule. Mantle shade ranges from medium slate in darkest pugetensis individuals (fig. 4) to moderated paler gray in many vancouverensis (fig. 7), while primary colour may fall anywhere between solid black (darker pugetensis, fig. 4) and light smoky gray (vancouverensis, fig. 7). Young birds of all 4 forms are considerably darker than in most subspecies (fig. 5). Orbital ring is highly variable, with some birds exhibiting a blend of deep pink and Western-esque orange-yellow (most often seen in pugetensis, where it has been incorrectly cited as an indicator of hybridization). Legs average duskier pink on pugetensis (fig. 4), intermedia, and vancouverensis (fig. 8), brighter and perhaps fleshier on prantyi (fig. 2), though this is not always consistent. Lighter birds found within this group's core range are likely non-breeders from more northern populations (e.g. hecatensis). This is the only GW group that is vocally distinct, with notably lower-pitched calls. 

Fig. 2: typical prantyi adult (Robert Raffel, Ebird web site)

Fig. 3: lighter pugentis adult (Mark Vernon, Ebird web site)

Fig. 4: darker pugentis adult (Sarah Frazee, Ebird web site)

Fig. 5: pugentis juvenile (Matthew Cvetas, Ebird web site)

Fig. 6: presumed intermedia adult (Thomas Barbin, Ebird web site)

Fig. 7: vancouverensis adult (Hayley Lester, Ebird web site)

Fig. 8: vancouverensis juvenile (Joachim Bertrands, Ebird web site)

Hecatensis

-L. g. fitzhughensis - Fitz Hugh Sound and Hakai area 
-L. g. hecatensis - throughout Hecate Strait and Haida Gwaii Island, north to Dixon Entrance
-L. g. nigrosubalaris - cryptic, largely concentrated around Dixon Entrance and likely north to Prince of Wales Island

Members of this well-studied group typically constitute what to the average gull-watcher is an ideal GW (fig. 10), featuring pearl gray mantles and wingtips, medium pink orbital rings (fig. 13) and legs, and mean-but-not-quite-hulking structural profiles (fig. 9). Juveniles and first-cycles (fig. 12) are almost always a marbled blend of pale gray-brown and white. With very few exceptions, these traits are present on all GWG from the Hecate Strait north and west across the GC range, and as such subspecific separation is somewhat less straightforward than in the pugetensis group. Hecatensis (especially fig. 10, fig. 11) can be considered the "nominate" form and will be referenced in comparison to other subspecies. To further discredit the confounding suggestion that all GW variation is clinal, primaries in the northernmost (of this group) nigrosubalaris average noticeably darker (fig. 14) than in fitzhughensis and hecatensis.

Fig. 9: fitzhughensis adult (John Reynolds, Ebird web site)

Fig. 10: hecatensis adult (Walter Thorne, Ebird web site)

Fig. 11: hecatensis adult (Walter Thorne, Ebird web site)

Fig. 12: likely hecatensis first-cycle (Teresa Weismiller, Ebird web site)

Fig. 13: nigrosubalaris adult (Steve Heinl, Ebird web site)

Fig. 14: nigrosubalaris adult (Steve Heinl, Ebird web site)

Fig. 15: undetermined third-cycle, most likely nigrosubalaris but possibly
hailing from farther north (Steve Heinl, Ebird web site)

Alascensis

-L. g. alascensis - coastal far southeast Alaska, primarily Alexander Archipelago and extending northwest to approximately Glacier Bay. 
-L. g. yakutatensis - coastal southeast Alaska, roughly from Yakutat area to Kenai Peninsula
-L. g. kodiakensis - Kodiak Island and adjacent mainland coast (Katmai area)
-L. g. argenteocinctus - cryptic, principally eastern and central Alaska Peninsula

This guild comprises the GWG of Alaska's gulf and southeastern islands, subtly quite intermediate between the classic hecatensis and more exotic forms found farther north and west. Most notably, mantle shade is an appreciably deeper steel (fig. 16) than in the hecatensis group, either contrasting with almost ghostly pale gray primaries in some alascensis (fig. 17) or remaining consistent through wingtips as in most hecatensis-types (most predominant in yakutatensis, fig. 18). A handful of yakutatensis are rather exceptionally dark-winged (fig. 19), especially in colonies near Icy Bay. Claims ofybridization with L. argentatus are likely exaggerated in the region, with many purported intermediate birds falling well in range for yakutatensis or kodiakensis (which often exhibit considerably blacker primaries, fig. 20, fig. 21). Poorly-known argenteocinctus is perhaps slightly bulkier overall (with some almost approaching certain Aleutian forms, fig. 23) and features consistent pale silvery wingtips (fig. 24). Juveniles and first-cycles are almost indistinguishable from marginally paler hecatensis-types, though some individuals appear more uniformly smudgy brown and lack "frosted" appearance (fig. 22). 

Fig. 16: alascensis adult (Victoria Vosburg, Ebird web site)

Fig. 17: alascensis adult (Marvin Hyett, Ebird web site)

Fig. 18: lighter/typical yakutatensis adult (Mark Moeller, Ebird web site)

Fig. 19: darker yakutatensis adult (Mark Moeller, Ebird web site)

Fig. 20: likely pure kodiakensis adult (Amy Clark-Courtney, Ebird web site)

Fig. 21: kodiakensis adult (Joshua Verbrugge, Ebird web site)

Fig. 22: presumed kodiakensis first-cycle (Robin Corcoran, Ebird web site)

Fig. 23: argenteocinctus adult (Ian Davies, Ebird web site)

Fig. 24: argenteocinctus adult (Lars Petersson, Ebird web site)

Borealis

-L. g. pribilofensis - St. Paul and St. George Islands
-L. g. fuscoauratus - mainland coastal southwest Alaska and Nunivak Island, north to Cape Romanzof
-L. g. borealis - St. Matthew Island and Norton Sound, rarely St. Lawrence Island

These "northern" GWG may represent the single most convincing argument for species-level treatment within the GC. Mantle and primary shade are several steps paler than in other groups, with KGS value plummeting as latitude climbs (fig. 26). This is most apparent in truly "arctic" borealis (fig. 30), where frosty tones often approach those of presumed ancestor L. hyperboreous. In fuscoauratus, the wingtips of many individuals appear uniquely dusky or gilded (fig. 29). The plumage of young birds is significantly lighter than in other groups (fig. 27, fig. 32). Overall side trends conspicuously upwards and appears to be truly clinal within this group; distinctive borealis birds are largest and bulkiest (fig. 31) with hyperboreous-esque squared heads, heavy bills, and broad chests, while fuscoauratus (fig. 28) and pribilofensis (fig. 25) average closer in size and proportions to the peninsular argenteocinctus form. This is a noteworthy example of truly clinal variation in the GC, where visual divergences are more often hopscotched without apparent gradation.

Fig. 25: typical pribilofensis adult (Steve Calver, Ebird web site)

Fig. 26: very pale pribilofensis adult, recalling L. hyperboreous (Ryan O'Donnell,
 Ebird web site)

Fig. 27: pribilofensis first-cycle (Ryan O'Donnell, Ebird web site)

Fig. 28: fuscoauratus adult (Susan Smith, Ebird web site)

Fig. 29: fuscoauratus adult (Rohan van Twest, Ebird web site)

Fig. 30: borealis adult (Nathan Goldberg, Ebird web site)

Fig. 31: borealis adult (Liam Singh, Ebird web site)

Fig. 32: borealis first-cycle, with presumed pugetensis
first-cycle for comparison (Joshua Covill, Ebird web site)

Fig. 33: unassigned borealis-type juvenile (Riley Wyna, Ebird web site)

Aleuticus

-L. g. pallidimantus - western Alaska Peninsula and Unimak Island
-L. g. unalashcensis - Fox Islands and Islands of Four Mountains groups
-L. g. adakensis - Andreanof Islands group
-L. g. aleuticus - Rats Islands group
-L. g. attuensis - Near Islands group

Arcing along the Bering Sea's southern edge, members of this group are among the largest and most variable of any Larus. Primary