[CT Birds] RE Todays curious gull in Windsor

Comins, Patrick PCOMINS at audubon.org
Thu Feb 21 07:30:51 EST 2013

Hi James:
Thanks for the input on Mark's photos. In answer to your questions, although I have limited experience with Slaty-backed in person, I would say that the structure is pretty darn good for Slaty-backed, or at least it was very wrong for Herring Gull.  The bird stands out structurally as much as it does in plumage.  It is a big bruiser and very wide-bodied, with a short wing projection beyond the wing, which I think are all good for Slaty-backed.  As to leg color, it seems to match very well with first cycle birds in photos from Japan.   I went back and looked at your 2009 bird, which is also quite intriguing.   One concern I have heard expressed is the 'string of pearls' of white spots in the primaries, which are making some folks think it may be some sort of Glaucous-winged, Thayer's or Iceland hybrid.  I think the later two are ruled out by the huge size and barrel chested appearance of this bird, but who knows if some strange combination could look like this.   I have seen photos of quite a few Slaty-backed in Japan that have this same feature and it is often mentioned as a good sign.  While we may not be able to rule out some sort of hybrid combination, I'm pretty confident that it is not a pale Herring Gull.  Primary pattern and structure just don't fit to me.

As to the  other bird of the week, I am now leaning more towards a hybrid Herring X Lesser Black-backed.  I had initially thought size and bill size "ruled that out", but while on the larger side (perhaps top 20% of herrings present), it could still represent a large hybrid.  Also, I had thought that the tertials and tail were wrong, but have subsequently seen a few photos of 2nd year lessers with a similar tail and tertial structure.

I do still have one reservation for the hybrid hypothesis though, and that is the retarded state of molt.   Generally all of the 2nd year lesser I've seen and the photos of hybrids I've seen have quite a bit of adult gray coming in, whereas this bird has very little.  It is almost hard to make up your mind as to whether you're seeing any.   Perhaps this could just be the Herring Gull genes dominating though.   Another sticky wicket is that some of the Appledore hybrids are now reaching breeding age and we could start to see some backcross individuals.


Date: Wed Feb 20 2013 13:23 pm
From: keenbirder AT yahoo.com

Exceedingly interesting Mark....thanks for posting. My only question would be - is the structure and leg color sound for Slaty-backed? It's tough to get a true sense of structure from the images. Cool find and images what ever conclusions you may draw in the end.

Best birding,


James P. Smith

Gill, MA

Patrick M. Comins
Director of Bird Conservation

Audubon Connecticut
185 East Flat Hill Road
Southbury, CT 06488

Phone: (203)264-5098 x308

Fax: (203)264-6332

pcomins at audubon.org
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