Yesterday on the Inwood Hill Park part of the Lower Hudson
CBC, Alan Messer found and photographed an immature gull on the pier at the end
of Dyckman Street on the Hudson River.. The bird intrigued
Alan and after consulting some references last night he sent me some photos
wondering about it being a Thayer’s Gull. I have circulated them to a few
people and the consensus is that it looks good for a Thayer’s. Alan saw the bird yesterday morning around 9:45 am.
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| possible immature Thayer's Gull (left) © Alan Messer |
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| possible immature Thayer's Gull © Alan Messer |
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| possible immature Thayer's Gull © Alan Messer |
Opinions? If anyone refinds the bird, please get the word out. I will be looking for it probably tomorrow morning.
[UPDATE: So far I have heard from about half a dozen birders, most with experience with the species, and all have said the bird looks like a Thayer's Gull, so I have taken the word "possible" out of the title of this post.]
What a find by Alan! I'm gonna try for it before work tomorrow.
ReplyDeleteOkay, so: what's the field mark difference between this and a juvenile herring gull? Both dark brown patterned, although the Thayer's seems a little lighter. Both pink legs, both black bill. Is it the lack of darker wing tips on the Thayer's, as seen on the herring gull?
ReplyDeleteThayer's is never an easy call, but there are a number of structural and plumage points on this bird that point to Thayer's. Starting with size, since it is near a Ring-billed Gull, you can see it is bigger than the Ring-bill, but apparently not as big and bulky as a Herring Gull. While there is much overlap in size between Herring and Thayer's, Thayer's average smaller. Much more important in this case is the bill. Thayer's have smaller, more slender bills than Herring Gull. This bird definitely seems to be smaller billed than a typical Herring Gull. The bill is also mostly dark, Herring's are typically much later at the base than this. In plumage, this bird is generally paler and shows less contrast than a young Herring Gull - more like a dark Iceland Gull. The primaries and tail band in particular are not as dark and as contrasting as you find in juvenile Herring Gulls - best shown in the flight shot. In a juvenile Herring Gull the tail band and primaries should be blackish-brown, not washed out gray-brown as in this bird. Overall, the bird is much more like a dark Kumlien's Iceland Gull than a Herring Gull, but the primaries are darker and show more contrast with the rest of the bird than in a typical Iceland. All told it is the combination of small things that points toward Thayer's.
DeleteThe best references are "Gulls of North America, Europe, and Asia" by K. M. Olsen and Hans Larsson (2003, Princeton university Press) and "Gulls of the Americas" by S.N. G. Howell and J. Dunn (2007, Houghton Mifflin).
Thanks!
ReplyDelete