Western Gull (Larus occidentalis), Glendale Recharge Ponds, Maricopa County

Tommy DeBardeleben found and photographed this Western Gull on the evening of 26 April 2010 at the Glendale Recharge Ponds around 5: 30 PM.  It sat in the pond and perched on a rock almost the entire time. It was first in the southeastern most basin of the six basins, and before it got dark the gull flew over to the northeast basin. It very likely spent the night.

There are only two previous records of Western Gull in Arizona (1946, 2001).  A possible 1979 record mentioned in Monson and Phillips (1981) could have been a Yellow-footed Gull. 

In this breeding plumage, the Western Gull and Slaty-backed Gull are the only possible birds, but Slaty-backed has never been recorded in Arizona. Both birds have pink legs, rather thick and heavy bills (Western heavier), and both also have broad tertials and a drooping "white skirt" (Sibley) on the secondaries. As shown in the pictures, Western usually has a darker iris (sometimes clear however), while in Slaty-backed it is usually clear to dirty yellow. But based upon these photos, what really nails this down as a Western is the underwing in flight, which has more visible black from below than a Slaty-backed. Slaty-backed would also have noticeable white subterminal spots, something that Western does not display as shown in these pictures.

26 April 2010, photo by Tommy DeBardeleben