Thayer's Gull (thayeri)

(last update: January 22, 2013)

Thayer's Gull 4cy (3rd basic moult) / sub-adult August

The Iceland Gull complex in Greenland – David Boertmann
British Birds 94, November 2001.

McGowan & Kitchener (2001) in their historical and taxonomic review of the Iceland Gull Larus glaucoides complex suggested that the form kumlieni is a hybrid population between the subspecies glaucoides and thayeri, a hypothesis which I find very convincing. I should like to supplement their review with some recent and mainly unpublished information front Greenland where all three subspecies occur.

The common and widespread large gull in low-arctic Greenland is glaucoides, breeding colonially along the coasts as far north as 74°N in west Greenland and 66°N in east Greenland. It may, however, breed even farther north in west Greenland since I saw a pair feeding newly fledged young in the Thule district (77°N) in 1995.

Ten years ago, kumlieni was considered a rare vagrant to Greenland, mainly in winter, with only nine published records (Boertmann 1994). These included a rather strange breeding record, involving a chick captured in west Greenland and held in captivity in Austria, which showed kumlieni wingtip markings when it attained adult plumage (Goethe 1986). A recent increase in observations at Nuuk, west Greenland (64°N), however, has revealed that kumlieni occurs regularly throughout the winter, from mid-August to early May, in small numbers (up to 1% of the number of glaucoides present). Farther north still, in the Disko Bay area (69°N), in late April 1996, I saw at least ten different adult kumlieni among thousands of glaucoides attracted to a fish factory. These ten showed a marked variation in wingtip melanism (ranging from one dark grey outer-primary vane to almost black markings on the upper side), as well as in iris colour (ranging from pale to dark, and not correlated with wingtip melanism).

During the summer, on the other hand, although I have observed tens of thousands of Iceland Gulls since 1974, in almost all parts of west Greenland, I have seen only one kumlieni, in the Thule district in 1998. ln the summer of 2001, however, a kumlieni was found breeding in a colony of glaucoides and Kittiwakcs Rissa tridactyla near Nuuk (M. Kviesgaard & L. Witting in litt.); unfortunately its mate was not seen.

The westernmost form, thayeri, bred in small numbers in the Thule district, in northernmost west Greenland, in the 1920s and 1930s (Salomonsen 1950). In recent years, many ornithologists have worked in this area, but have never reported thayeri, although I have urged them to look for this particular taxon. The only published records of thayeri from this district in recent years are of a small number of individuals seen in early autumn 1987 at Thule Air Base, and a few adults which l saw at the same site in 1994 and 1995. Outwith the Thule district, thayeri has been recorded a few times in spring and summer in the central and northern parts of west Greenland (Boertmann & Mosbech 1999).

All in all, therefore, glaucoides is the widespread and common subspecies of the Iceland Gull in low-arctic Greenland. The intermediate form, kumlieni, seems to be increasing as a winter visitor (although this could also be explained, at least in part, by an increase in ornithological activity during the same period), but only two breeding records are known. The form thayeri has probably disappeared from Greenland as a breeding bird, but occurs as a spring and summer vagrant.

References, see PDF.