13 October 2014

More Gull Specimens From Chicago's Field Museum

I again had the pleasure of looking through the gull collection at Chicago's Field Museum last Friday. The most interesting specimen studied during my visit was this first cycle bird:

Monterey County, CA. March 1909.
It was identified as a California Gull (L.californicus), but the bill's pattern and shape didn't seem consistent with that species. I also felt the lack of post-juvenile scapulars seemed wrong for a 1st cycle California Gull in March. Herring Gull crossed my mind but the uppertail coverts and outer tail edges didn't agree with Herring. I left the specimen alone and wasn't comfortable labeling it. Thanks to Steve Hampton and Tristan McKee - both gull aficionados from California - for steering me in the right direction on this one and suggesting "Western Gull" (which I fully agree with). Here are Tristan's comments regarding the scapulars:

"...looks just like a March Western. The small size is probably a preparation thing. My impression is that ALL the juvenile scaps have been replaced, as expected. Western's preformative molt is so early that the feathers come in quite young-looking".

Given that it was collected in Central California in March is another reason to believe it's indeed a Western.
The last few days have been very educational for me as several people have cautioned me on the condition of old specimens housed in museums. In particular, taxidermist Keith Mueller had many useful comments to make that were taken to heart:

"Be careful about relying on bill and tarsii measurements on any Taxidermy mount (unless an cast artificial head is used) especially very old skins whether full mounted or drawer skins. These dried skins can dry and shrivel so varied that it would be impossible to gauge the extent or the shrinkage and distortion, and for that matter, color fading. Even plumage coloration fading and handling wear can be completely different than the actual color values. I have been a Taxidermist since 1974 and have seen s o much variation in fading and distorted bare parts, actually this info is almost useless in relation to reality."

"Amar, the colors can do just about anything as the bill dries. I have seen a few lighten up, but mostly they get darker and often turn blotchy and uneven."

"A skin that is that old will be subject to quite a bit of degradation through time, especially if they are not cared for properly. Markings can change also when the feather texture degrades giving a false optic as to the actual shapes and forms of the markings. Evaluating study skins can be challenging with all these factors taken into consideration. The best approach I have found is to compare a drawer skin to an actual photograph and make your conclusion that way."

"When a skin is prepared for a drawer skin, how the "inside" of the skull is handled will also change the shape of the skull and bill. The concept behind drawer skins is to prepare the skin so it can be examined, referenced and researched for time."

It's becoming clearer to me that size measurements and bare part colors from old skins - perpared decades ago - are to be carefully considered, especially if no in-field experience is tied to these values. This makes the measurements taken from live birds (such as those found on gullresearch.org) much more meaningful. I wonder what implications this has on measurements found in the literature, specifically our gull guides.

Other interesting specimens from this visit include a leucistic 2nd cycle type Laughing Gull:

New Jersey. Early June.
The faded hood feathers are interesting - this might be a consequence of long-term feather deterioration exhibited by old skins, or a result of this bird's leucism. Notice the complete fading of the bill color! This is a clear example of a dark bare-part color becoming light, just as a light bare part color may become darker when housed over a long period of time.

There are lots of other interesting skins that I saw during this visit and I'll eventually get around to posting all or most of them with comments, but for now, I'll finish with a set of four folded wingtips, from darkest to lightest. Care to guess what species these are? The answers are posted below.

The two on the left were identified as Thayer's Gulls (Alaska and British Columbia) and the two on the right as Iceland Gulls (Nova Scotia). The third bird was actually collected by Earl Godfrey.

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