Birding Alaska

Back in the Bering Sea on the NOAA Ship Oscar Dyson.  We left Kodiak on April 23rd and we’ll finish this cruise in Dutch Harbor on May 3rd. The mission of the cruise is to service oceanographic moorings in the eastern Bering Sea.

Young Spotted Seal Phoca largha, Bering Sea, 28 April 2010.

Thayer’s Gull Larus thayeri and third-cycle Glaucous Gull L. hyperboreus, Bering Sea, 28 April 2010.

While watching seals on a small flow of brash ice about 60 miles north of Unimak Island today I noticed this adult Thayer’s Gull in a group of Glaucous and Glaucous-winged Gulls. Thayer’s Gulls are probably casual in the Bering Sea. This adult is separated from Herring, Vega, and Herring x Glaucous-winged Gull hybrids by outer primary pattern, its smallish bill and rounded head, and relatively long primary projection.

First cycle Thayer’s Gull Larus thayeri, Homer Spit, 25 February 2010.

Thayer’s Gull is a good find in Homer in the winter.  This first cycle bird was in a flock of 4,000 gulls at the offal discharge site on the end of the Homer Spit.  It was first reported by Martin Renner on 21 February.  Rich MacIntosh and I found the bird again on 25 February and got these photos.  Most of the gulls were Glaucous-winged L. glaucescens, and Mew Gulls L. canus brachyrhynchus.  Also present in the flock was one first cycle Glaucous Gull L. hyperboreus and an adult Herring Gull L. argentatus smithsonianus.

Structurally this Thayer’s Gull is identified by it’s smaller size, more rounded head, smaller and narrower bill, and wings that are proportionately longer than the abundant Glaucous-winged Gull.  Also, on this Thayer’s Gull the outer primaries, tail and tertials are darker than the rest of the upper parts–this is evident on both the sitting an the flying bird.  Note that the primaries of this Thayer’s Gull are dark brownish with pale fringes.  A first cycle Herring Gull would have more blackish primary tips lacking the pale fringes.  The upperparts of a first cycle Glaucous-winged Gull is very uniform in tone and the primaries, tail and tertials do not contrast with the rest of the upperparts.  See the next two photos for comparison with Glaucous-winged Gull.

First cycle Glaucous-winged Gull Larus glaucescens, Cordova, 30 December 2005.

First cycle Glaucous-winged Gull, southern Bering Sea, 26 February 2009.

On both of these Glaucous-winged Gulls note the completely uniform tone of the upper parts.  There is no contrast between the tail, outer primaries, tertials and the rest of the upper parts.