31 October 2017

October 2017 Quiz

Age: The flight feathers, all-white tail and body feathers point to an adult-type, large white-headed gull (LWHG).

Identification: Our October bird is a black-backed gull with pink legs. In North America, we have two regularly occurring black-backeds with pink legs: Western and Great Black-backed, but this individual is neither.

Structurally, both Western and Great Black-backed Gull have noticeably different bills than what's seen here. Western typically shows a brighter yellow bill with a wider gonys angle - a bulbous-tipped bill, if you will. Great Black-backed's bill is much more stout and thick - a strong bill all throughout with a blunt tip.
Adult Western. Note the bulbous-tip and mustard-yellow orbital ring.
San Luis Obispo County, California. January.

Adult Great Black-backed. The gonys is swollen and the bill is thick throughout.
 Huron County, Ohio. November.

Notice in both of the images above there is very little in the way of head markings. Both of these black-backs average much less head markings than all of our other LWHGs, even in basic plumage. Also, neither possesses the menacing stare of our quiz bird, with eyes that appear to be encircled with mascara.

Perhaps of most importance when identifying this month's quiz gull is the wing pattern. Notice the remarkably thick white trailing edge, a glaring field mark that screams Slaty-backed Gull.

Here's a cropped image of this gull's right wingtip:

The white on the inner primary tips eats into the black edges with a so-called "string of pearls" on the adjacent mid-outer primaries (white tongue tips abutting the black sub-terminal bands on p5-p8).

A species that's generally increasing in North America, particularly on the Great Lakes in winter, this month's Slaty-backed Gull was photographed in Lake County, Illinois. February.