Possible Thayer’s Gull @ Windsor Landfill – Patrick Comins

23 02 2009

Patrick Comins found this possible Thayer’s Gull up at Windsor Landfill. Just putting these photos up for him for so that CTbirding listserve members can have a perusal of them. The pictures look pretty promising for Thayer’s to me, but I am basing this more on booksmarts than field experience with this particular species. I’m sure Patrick would be happy to see any informed feedback. Below are Patrick’s initial postings on the bird from the Connecticut Listserve:

Feb 20

I have some decent photos if anyone would like to have a look. I’d say Iceland
is pretty much ruled out but there is thoughts that it might be a recessive
form of a hybrid HerringXGlaucous since the bird isn’t especially small. It
appeared to be smaller than the surrounding Herring Gulls in the field, but
certainly not appreciably smaller. Some features that aren’t typical of
HerringXGlaucous include a nearly all black bill and a smudgy hooded appearance
around the eye, much like a Thayer’s. I have had some funky Thayer’s-like Gulls
in the past so I am always a little hesitant to make that call. In any case,
maybe I can get the shots posted online somewhere or I’d be happy to email a
bunch if anyone wants to venture an opinion.

I also caught a brief look at an adult or near adult black-backed gull with
marked head streaking, and pink legs, but it was a very brief look and I’d only
put it in the ‘something to keep your eyes open for’ category.

Feb 23

For anyone who might be considering going up to the Windsor Landfill trying to
add Thayer’s to their CT list, the ID pendulum seems to be swinging back
towards Thayer’s for the bird found on Friday. A hybrid HerringXGlaucous just
doesn’t make sense to me for a bird with a bill that is blacker and with more
extensive black than a typical smithsonianus at this time of year. There is
some fading at the base of the lower mandible, but otherwise very black. In
addition, while the bird is larger than the Thayer’s that have been
photographed in CT, it is still smaller than your average Herring Gull and well
within the range of variation I think (there is overlap in size between the two
species). Bill structure also looks better for Thayer’s than Herring or
Glaucous or in between the two. The open wing pattern looks pretty good to me
for Thayer’s and atypical of ‘Nelson’s’. If anything, perhaps the bird is a
hybrid HerringXThayer’s, but that combination is unrecorded as far as I know.

Another Thayer’s feature is the uniform color and lack of blotchiness on the
breast and back, those diffuse streaks on the neck and fine pattern of
streaking on the crown, all of which say Thayer’s to me. The black face mask is
also good for Thayer’s, but not Glaucous nor Herring and the retained juv Scaps
would also fit Thayer’s. Legs are also deeper pink than most smith, another
Thayer’s feature. One feature that was troubling me was the relatively short
primary projection, but after looking at many photos of Thayer’s Gulls I think
it is fine. Birds with longer primaries are sometimes thrown into the dark
Iceland Gull bucket, so maybe it is even good. At least we know this bird isn’t
an Iceland Gull.

I am hoping to find a way to post some of the photos so we can get some input
from the west coast, but for now the bird is still worth chasing down if you
want a Thayer’s for CT. While I wouldn’t be totally stunned if this bird isn’t
a Thayer’s and I am still open to good arguments as to why it might not be, I
would be surprised. It is certainly an interesting bird in any case.