Bird of the Month: Iceland Gull
By Andy McCormick
Iceland Gull by Brian Wulker
Scientific name: Larus glaucoides
Length 23””
Wingspan 54”
Weight 2.2 lb (1,000 g)
AOU Alpha Code ICGU
A 2017 decision by the American Ornithological Society lumped the gull formerly known as Thayer’s Gull with Iceland Gull making it a subspecies of Iceland Gull.
“The taxonomy of the Iceland Gull is confusing and has been much disputed. The Iceland Gull was formerly treated as two species…, but the two were recently merged …. The Iceland Gull is among the least known of all North American gull species and few studies have been dedicated to their natural history” (Snell, Pyle, and Patten).
AN ARCTIC GULL SPECIES
Iceland Gull is a high Arctic gull that breeds in the coastal regions of the Canadian Arctic Archipelago and Greenland. It is medium-sized and slightly smaller than a Herring Gull. It nests on sea cliffs on islands in areas that are inaccessible in winter (Alderfer). Due to the remote environment, research on Iceland Gull is limited and little is known of its breeding habits. The nest is a bulky mound of grasses, moss, and debris probably built by both sexes. The length of the incubation period and age at fledging are not known (Kaufman).
Iceland Gulls forage on cold-water fish such as Capelin and Eulachon, both small forage fish of the smelt family. They spend most of their time in the intertidal zone typically taking the fish from the surface of the sea. They will also land on the surface and pick fish from the water. At more southern latitudes during winter they will forage more closely to humans on lawns, around fishing wharfs, and in garbage dumps.
SUBSPECIES STATUS AND DISTRIBUTION
The three subspecies of Iceland Gull breed in close proximity to one another, but in distinct areas of the Canadian and Greenland Arctic. The former “Thayer’s Gull” (L. g. thayeri) breeds in small island colonies on the western and northern edges of the breeding range. The cliffs on which they nest often face the ocean. These gulls will winter on the western coasts of the Pacific Northwest from British Columbia south to Washington, Oregon, and California (Snell, Pyle, and Patten). One of the reasons for previously considering Thayer’s Gull as a separate species was because it is the only subspecies that winters on the west coast of North America, and thus it is the Iceland Gull most commonly seen by Washington birders.
The subspecies known as “Kumlien’s Gull” (L. g. kumlieni) breeds in the Baffin Island area, and the nominate Iceland Gull (L. g. glaucoides) breeds the farthest east in Greenland. There is evidence of some interbreeding between Thayer’s and Kumlien’s Iceland Gulls and this is one of the reasons these birds were lumped again (Alderfer).
PLUMAGE VARIATION
The Iceland Gull was also previously split because the Thayer’s Gull more closely resembles a Herring Gull (Larus argentatus) and the Kumlien’s Gull is similar to a Glaucous Gull (Larus hyperboreus). The Thayer’s has dark wingtips with white mirrors and white under the wing. The Kumlien’s has white wingtips with gray markings. All four of these gulls are considered part of the large group of white-headed gulls, which is how they appear in their adult plumage.
A thorough discussion of the Iceland Gull can be read at the Cormell Lab of Ornithology’s Birds of North America.
A WORD ON THE THAYER’S GULL CONTROVERSY
Thayer’s Gull was split from Herring Gull in 1973. It was determined that based on phenotypic data such as size, color, shape, and behavior that it was closer to Iceland Gull than Herring Gull. One study completed in 1966 had suggested that Thayer’s and Iceland were separate species and the AOS agreed. However, in recent years the data from the 1966 study was found faulty and some reviewers consider it fraudulent. When that study is removed as evidence from consideration, there remains little evidence that Thayer’s Gull is a separate species. In 2017 the AOS decided they no longer had evidence to maintain Thayer’s at the species level, and decided they had to lump Thayer’s with Iceland until an acceptable study can be undertaken in the contact zone of Arctic Canada. However, this is a difficult environment for bird study, and at this time there is no one planning such a study in the near future. So, Thayer’s Gull is now an Iceland Gull.
References available upon request from amccormick@eastsideaudubon.org.