On Thursday, 9 Apr 09, Larry Gara and I spent about an hour with the Lesser Black-backed Gull Larry discovered the day before (8 Apr 09).  The bird was seen on and just off the beach in good light, standing, wading, swimming and flying.  The bird was reasonably approachable so that we were able to get good views and passable photos (see below).

The bird was in very nearly adult plumage.  It was intermediate in size between the ring-bills and Herring Gulls that were conveniently lounging close by.  The mantle was dark gray and very uniform.  The head was white, not streaked or mottled at all.  The legs and feet were yellow.  The beak was yellow with a dark smudge near the tip that was being supplanted by a red gonydeal spot.  The secondaries were broadly tipped with white.  The primaries were long and tipped with little lenses of white.  There was a distinct white mirror near the end of P10.  When the bird took flight, we saw that most of the rectrices were white but some rectrices with dark tips were retained.
Back home, I consulted Howell & Dunn, “Gulls of the Americas,” Olsen and Larsson, “Gulls of North America, Europe, and Asia;” and Peter Pyle’s new Volume 2 of his “Identification Guide to North American Birds.”  It is our opinion that this bird is near the end of the third cycle, nearly into its first definitive basic plumage.  It has all the necessary characteristics except for some retained second cycle rectrices and the remaining black smudge on the bill with an emerging red gonydeal spot.
Larry also had a Lesser Black-backed Gull at this location in 2002.  That bird stayed around for months, so we are hopeful that this bird will do the same.
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Lesser Black-backed Gull swimming.  Note projection of the primaries.  The mirror on P10 is evident on the right wing folded over the tail.  All of the visible primaries are tipped with little white lens-shaped patches.  The broad white tips of the secondaries and tertials are very dramatic.  The bill is marked by the dark smudge that is characteristic of the second cycle, but one can easily see that it is being supplanted by the red gonydeal spot of the full adult bird.  Note yellow iris.
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Lesser Black-backed Gull taking flight.  Note broad white tips on secondaries, tertials, and scapulars.  The white mirror on P10 is very evident.  In this picture the tail is too compressed to reveal any of the rectrices with black spots retained from the previous plumage.