probable Black-headed x Ring-billed Gull - Plymouth Breakwater - Plymouth, MA - 11/6/11
by peregrinus01
This gull was first seen loafing on exposed flats just in front of the Plymouth Breakwater free-parking lot on Water Street around 3:30 pm on 11/6/11. It was in with a large number of Ring-billed and Herring Gulls, and was still present as dusk descended. I digiscoped the photos from about 75 yards.
I originally identified the bird as a second-winter BHGU, but after further scrutiny of photos and consultation with others, it seems as if this bird may in fact be a Black-headed x Ring-billed Gull hybrid.
Reasons for being a pure second-winter BHGU: dark tip on bill, fading/partial hood, less than deep red bill and legs. In addition to this, in flight I was able to see a well defined translucent-white primary triangle. The bird was noticeably smaller than the surrounding RBGU.
The inconsistencies for a pure BHGU begin by looking at overall structure and primary patterning. In the photos, the bird seems too bulky and square headed to be a BHGU. The bill is stubby and similar to that of a RBGU. It also appears that there are white windows in the primaries, which is consistent with RBGU, but not BHGU.
If this is indeed a BHGU x something, then the most likely candidate is RBGU.. both for the above listed reasons and that these species both breed in the Canadian Maritime, where most BHGU that appear in New England originate from. Common Gull cannot be eliminated for certain, but is much less likely.
