A Black-tailed Gull (Larus crassirostris)
at Herring Cove Beach, Provincetown, Massachusetts
1 November 2008

Blair Nikula

This Black-tailed Gull was associating with a large (1500+ birds) aggregation of gulls feeding on the beach at Herring Cove in Provincetown on 1 November 2008. It is in an essentially adult-like plumage, but the brownish markings in many of the coverts suggest either a 3rd winter or perhaps a 3rd summer bird molting into its first adult winter plumage. The bird was present, albeit sporadically, through at least 7 November. All photos were taken with a Canon 40D and Canon 100-400mm IS lens and are copyright 2008 Blair Nikula.

Salient features evident in the first photo are the slate gray mantle; attenuated profile with long primaries (despite P10 not being fully grown) and a shallow sloping forehead; long greenish-yellow bill with black subterminal band and red tip; and greenish-yellow legs (which looked even greener in the field than in these photos).

A direct comparison with an adult Ring-billed Gull. The Black-tailed was about the size of a large Ring-billed.

The broad, solid black subterminal tail band and white terminal band are obvious here. Note also that the outermost primary (P10) is still growing.

Note the brownish tinge in many of the coverts, suggesting a less than fully adult bird. Curious is the gaps in both wings apparently the result of a missing P2; I'm at a loss to explain this in a bird that otherwise appears to be just completing its primary molt.

A portion of the gull concentration at Herring Cove - 1500+ individuals of at least 9 species were present.

The attraction: masses of 1" long, shrimp-like mysids, probably either Neomysis americana or Mysidiopsis bigelowi, that had collected in windrows along the high tide line. (Thanks to Karsten Hartel of the MCZ for providing the identification of these creatures.)

The windrows of mysids along the upper beach.