Another Presumed Hybrid
Lesser Black-backed Gull X Herring Gull

Provincetown, Massachusetts - 31 January 2010

Blair Nikula

The adult gull depicted below was photographed at Herring Cove Beach in Provincetown (Barnstable County), Massachusetts on 31 January 2010. Just about every feature of the bird suggest it is a Lesser Black-backed X Herring Gull hybrid. All images were taken with a Canon 40D and a 100-400 IS lens.

When I first spotted the bird it was on its belly facing away and I assumed it was a Lesser Black-backed. However, the mantle appeared a bit too pale and the bill rather thick for that species. When it stood up, the legs, although distinctly yellowish, were not as pure or bright a yellow as I would expect on an adult LBBG. In profile the rear end of the bird has the rather long-winged, attenuated look of a LBBG, but up front seems pretty stocky, more like a HEGU.

The bird was pretty close in size to a HEGU and a bit large for a LBBG. The mantle, though distinctly darker than the adjacent HEGUs, was a bit paler than a typical graellsi LBBG, though perhaps not out of the range of that form.

As is typical for these birds, the yellow on the legs was most obvious from behind and on the "knees."

The primary pattern seemed intermediate between LBBG and HEGU as well. The extensive white tip on P10 and the large white mirror on P9 are suggestive of HEGU, while the relatively extensive black on P5 (and more extensive black on the bases of P10-P8?) are suggestive of LBBG. The primary pattern actually seems like a pretty good match for some forms of Yellow-legged Gull as well, though other features (e.g., the slate-gray rather than blueish-gray mantle and thick head streaking)  do not fit that species.

Curiously, P9 on the right wing (only) was just partially grown; since this was not the case on the left wing, presumably that feather was being replaced after the original was lost or damaged.