Date: 1/4/18 5:15 pm
From: Walter Marcisz <wmarcisz...> [ILbirds] <ILbirds-noreply...>
Subject: IBET RBA Slaty-backed Gull - Cal River from Stony Island Overlook, Chicago (1-4-18)
I arrived at the Stony Island overlook over the Calumet River just south of Deadstick Pond, Chicago, IL (ebird hotspot: Lake Calumet area – Turning Basin #5) at 1:15 pm on Thursday (4 January 2018). I had just set up my scope when Andrew Aldrich arrived. A minute or two after Andrew arrived, I spotted an adult black-backed gull on the ice with a broad white tertial crescent. For sure, a good candidate for Slaty-backed Gull. I took some photos. When I went to my car to get some bread to throw, Andrew was able to see one of the legs – it was pink.  Then an eagle flushed the all of the gulls, but after a while they reassembled on the ice. At that point I got a good look at the Slaty-back standing on the ice – both of its legs were bright pink. My one distant flight shot is somewhat less than diagnostic. Although it hints at the string of pearls, the resolution is really not good enough to discern the wingtip pattern. Andrew secured a really good flight shot which to me looks diagnostic for SBGU – hopefully Andrew will post it. My “at rest” photos tell the rest of the story: dark mantle (at the dark end of L. f. graellsii LBBG); very broad white tertial crescent; overall size smaller in length (but bulkier) than the adult HERG behind it; primary projection shorter than the adult HERG behind it; white head with menacing dark eye-shadow and dusky “neck boa.” This is an adult SLATY-BACKED GULL.

Photos at the link: 

https://www.flickr.com/photos/38600858@N06/24640217637/in/dateposted-public/

Walter Marcisz
Chicago, Cook Co.


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Posted by: Walter Marcisz <wmarcisz...>
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