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Sunday, 24 January 2010

The variability of NORTH AMERICAN HERRING GULLS

Last week a friend lent me her new Canon digital SLR with a moderately long lens (250mm). It was my first chance to photograph birds by other than digiscoping in the last 10 years, and it was my first experience with a digital SLR. The big excitement for me was shooting flying birds. (I took over 3,000 photos in the first weekend.) I used the opportunity to try to document some of the variability in North American Herring Gulls (Larus smithsonianus) that visit central New York in winter. I have put a number of shots at

http://picasaweb.google.com/KevinJ.McGowan/HerringGullsInIthaca.

These were all taken over 2 days at the Cornell compost facility east of Ithaca (I will be adding some more from the next weekend, eventually). I have been working at this particular facility for over 10 years now, mainly looking for marked crows for my long-term study. In the last 5 years or so we have had a bonanza of different gull species occurring there, recording Ring-billed Gull, Laughing Gull (1x), fly-over Bonaparte's, Herring Gull (including some European-looking individuals), Iceland Gull (ca. dozen yearly), Thayer's Gull (at least 5 1cy), Lesser Black-backed Gull (ca. 10 yearly), Great Black-backed Gull, Slaty-backed Gull (2 adults), Glaucous Gull (ca. 2-3 yearly), and hybrids Herring x Glaucous (Nelson's), Herring x Lesser Black-backed, and possibly others.

Herring Gulls breed in New York state, but not in the near vicinity of Ithaca. From reading band numbers we know that we get some from breeding colonies along the St. Lawrence River and from Maine. Where else they come from, I don't know.

I see a huge amount of variation in adults in terms of dark head markings, bill markings, and pattern of dark in the wings. We see individuals with the underside of the wingtips as dark as Ring-billed Gulls and some as white as Thayer's. I posted some examples of adults a while ago at http://www.birds.cornell.edu/crows/HEGUadults.htm. Whether the extremes represents variation within a single breeding unit or the occurrence of several different and distinct clusters from disparate locations is unknown.

The examples posted at http://picasaweb.google.com/KevinJ.McGowan/HerringGullsInIthaca
are not a random sample; they are essentially birds that flew past my car close enough to be photographed and at the right angle for sunlight to illuminate them under the wings. I tried to exclude multiple pictures of the same individual. I did not include multiple photos from the same sequence, but I will not guarantee that the same individuals are not represented more than once. I have thousands of digiscoped photos of immature Herring Gulls showing an incredible mix of characters from past years, but, oddly, right now we have primarily adult Herrings present, and they represent the bulk of what I have posted.

Kevin J. McGowan, Cornell Laboratory of Ornithology, 159 Sapsucker Woods Road, Ithaca, NY 14850, kjm2@cornell.eduhttp://birds.cornell.edu/crows/