Thayer's-like Wingtip Pattern in a Herring Gull

Ron Pittaway and I observed this Thayer's-like Herring Gull in Ajax on Lake Ontario on 5 February 2016. A gray tongue reaches the white mirror on P9 and it has the "string of pearls" pattern not seen on most Herring Gulls. A further distinction from most Thayer's is the more extensive black on P10 with a gray tongue not joining the white tip. Average Thayer's has a pale grayish or whitish tongue joining or almost joining the white tip on P10. Note: Herring Gulls with a Thayer's-like wingtip pattern appear to be females (Macpherson 1961). An adult female Herring Gull with a Thayer's wingtip pattern was collected in Ottawa, Ontario. It is in the Canadian Museum of Nature. We also examined a female Herring Gull with a Thayer's wingtip pattern from Yukon in the Royal Ontario Museum in Toronto.

This Herring Gull's folded black wingtips have larger white primary spots than on most Herring Gulls. Adult Herring Gulls in winter often have black near the bill tip such as on this individual, but this is not usually seen on winter Thayer's. The eyes are clear yellow which is rare in Thayer's. The yellow bill lacked greenish tones typical of Thayer's in winter. Also, the orbital ring is yellowish whereas Thayer's is purplish. 5 February 2016.

The undersides of the wingtip show more blackish than on most Thayer's. Compare with typical Herring Gull below which shows more black on undersides of the primaries. 5 February 2016.

Typical Herring Gull show extensive blackish on the undersides of the primaries. 5 February 2016.

Acknowledgements: We thank Michel Gosselin of the Canadian Museum of Nature for information on Thayer's-like Herring Gulls.

Literature Cited: Macpherson, A.H. 1961. Observations on Canadian Arctic Larus gulls, and on the taxonomy of L. thayeri Brooks. Arctic Institute of North America Technical Paper 7:1-40.