QUIZ GULL #4 (answer is below)

The correct answers to Quiz Gull #4 are Herring Gull or Herring x Thayer's Gull hybrid. Such a simple adult gull, yet so confusing. The pink legs, pale gray mantle, and black in the primary tips immediately eliminate the dark-mantled gulls, all gulls with yellow legs, and Iceland and Glaucous Gulls.

The bill size and shape and the smallish head and body seem perfect for Thayer's, which is more dove-like than Herring. Note how much smaller the leg diameter is on this bird, compare to the larger Herring Gull behind it. Also, the dark eye is an excellent mark. The head markings seem more smudgy than streaky and the bill lacks any dark mark near the red mark. These also point away from Herring and more towards Thayer's.

However, look at the underside of P10-- it's black with a white mirror. This is fine for Herring, but completely wrong for Thayer's. In flight, the primary pattern resembled Herring Gull. Could this be a small female Herring Gull? A small percentage (less than 1%) of smithsonianus Herring Gulls have dark irises. Could this be a small female Herring also with a dark eye? Or could this be a Herring x Thayer's hybrid? I'm not sure which is more likely, and I'm not sure which way I lean...

The photo was taken February 24, 1998 by Mike Rogers (copyright 1999) in the San Francisco Bay Area, CA.