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Literature Review: Hybridization in Iceland and Thayer's Gulls

by Ron Pittaway

A recent paper on "Hybridization and changes in the distribution of Iceland gulls (Larus glaucoides/kumlieni/thayeri)" was published in the J. Zool., Lond. (2000) 252: 517-530 by The Zoological Society of London in the United Kingdom. The authors are D.N. Weir (deceased 15 August 2000), A.C. Kitchener and R.Y. McGowan. I thank Michel Gosselin of the Canadian Museum of Nature for sending me this timely paper.

Abstract follows in quotations:

"Three Iceland Gull taxa were defined mainly from adult wingtip melanism. Up until about 1860, nominate glaucoides (no melanism) was known to breed from Greenland to western High Arctic Canada, but by about 1900 it was essentially confined to Greenland. Until 1860, thayeri (most melanism) was known only from western High Arctic Canada, but from 1900 to 1980 it was found throughout High Arctic Canada and a small part of north-west Greenland. At high latitudes in Canada it replaced glaucoides, with which it was formerly sympatric in the west and probably interbred. The first known kumlieni (intermediate, variable melanism) were from west Greenland in the 1840s, and by 1900 the western and northern limits of most of its breeding range in the eastern Canadian Low/High Arctic were known. The range of kumlieni lies between those of thayeri and glaucoides and overlaps both:kumlieni bred in Greenland by 1964. It freely interbreeds with thayeri and probably with glaucoides. Winter ranges of glaucoides and thayeri have changed little since they were first determined for glaucoides by 1860 and for thayeri by the 1920s. However, winter adult kumlieni was unknown from Greenland to the British Isles until 1900; there were a few records prior to 1915 and progressively more after 1950. The study adds to the evidence that kumlieni represents introgressive hybridization by western thayeri into eastern glaucoides."

Here are some interesting statements from the paper:

1.

"Compared to other hybrid and parent distribution changes in large gulls...the extent and speed of change in Iceland gulls has been extreme." "We believe that thayeri spread east and interbred with glaucoides, giving rise to the variable hybrid kumlieni. As the eastward shift continued, the hybrid zone moved east and introgression may now extend to the eastern limits of the greatly reduced range of glaucoides."

2.

"In the Iceland gull there were rapidly shifting distributions of both parent and hybrid taxa, but kumlieni is now probably more numerous than thayeri, and glaucoides may be 10 times more abundant than either of them." Population estimates are 4,000 to 6,000 pairs of thayeri in Canada; 10,000 pairs + or - 50% ofkumlieni in Canada; and probaby less than 80,000 pairs of glaucoides in Greenland.

3.

"...thayeri and glaucoides need not necessarily be one species; it is only necessary that kumlieni is intermediate between them." "Whatever taxonomic treatment is adopted, Kumlien's gull is a useful common name for the hybrid population and it commemorates a man who made an outstanding comprehensive study of Arctic natural history..."

This paper is based on journals and museum documents from historical and more recent expeditions to the Arctic, examination of skins in museums, and includes about 124 cited references.

There is a lot more in the paper than I have outlined. Students of gull taxonomy will want to have their own copy of this paper, which is the most significant addition in years to the ongoing discussion about Iceland, Kumlien's, and Thayer's Gulls.

This note is reproduced by permission February 2001. Copyright 2001 with the author Ron Pittaway (Minden, Ontario). Thanks to Jean Iron for facilitating this production.

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