24 July 2013

Arctic Gull Specimens at CAS

I visited the Chicago Academy of Sciences the other day (twice this month) to review, yet again, a very important Western Gull specimen taken in Chicago, 1927. After finishing up with that work, I took some time to look over a few "fun" skins...

First cycle Ross's Gull (left) with similar aged Black-legged Kittiwake.
The question to ask yourself is how one would tell the Ross's from a Little Gull in this plumage. Besides the lack of any black on the crown (which may be absent in a minority of Littles), the primary pattern is helpful. With first cycle Little Gulls, the black tips on the mid-primaries tend to merge and form a rather solid black portion to the outer edge of the stacked primaries (Martin Reid describes the dividing edge as a "saw-tooth" pattern). In Ross's, the mid-primaries show black tips that are each almost entirely surrounded in white. This is more or less the difference one would be looking for. Of course in flight the identification should be much easier (if one was mentally prepared to call out a 1st cycle Ross's to begin with). Also of note is bill size. It dawned on me while looking at the two trays of ROGU specimens at the museum that Ross's has a very petite bill - very pigeon-like. Indeed, Ross's bill is notably smaller than Little's.

These two are almost exactly the same exact size and this is how the field guides describe them, each about 12.5 inches in length.

Ross's (left). Sabine's (right).

The Ivory is clearly a juvenile. Interestingly, all of the Ivory specimens (even the adults) had this strong "creamy-yellow" tinge to them. It may be unique to this species post-mortem as I did not notice it with any other white feathers on the other gulls. And yes, Ivory Gull is larger than BLKI.

Black-legged Kittiwake (left) with Ivory Gull.

Now for a group photo of some of the most sought after arctic gulls on the planet:

From left to right: Ross's, Black-legged Kittiwake, Ivory and Sabine's Gull.

All of the specimens were collected in Alaska and off its shores. The Ross's was collected in Barrow in September. Here's a first alternate Ross's Gull collected in Barrow in June:

1st alternate Ross's Gull.
The black necklace is usually obtained by about 10-12 months of age and is not always nicely defined as in alternate adults.

A special thanks to Dawn Roberts for again allowing access to the collection and putting up with my childness while reveling over these skins.