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QUIZ GULL #7


Hint: photo taken in early February.

ANSWER:

The correct answer to Quiz Gull #7 is second-winter Slaty-backed Gull (with partial credit for Great Black-backed). Here's my reasoning:

Yikes! It's a bunch of feathers. Okay, calming down, we see the bird must be facing away from us. That's the back and scapulars up high, the lesser and median coverts on the middle right edge, the greater coverts nicely displayed below, and the tertials just left of center. There's also some folded primaries down there on the left side.

Let's age this thing first. The apparent adult gray on the back and scapulars (combined with immature plumage elsewhere) and the marbling on the tertials and greater coverts are very typical of second year birds. Now let's narrow the field. The adult gray is very dark, nearly blackish. Conservatively, let's narrow the field to Great Black-backed (marinus), Lesser Black-backed (intermedius), "Baltic" Lesser Black-backed (fuscus), Kelp, Slaty-backed, and possibly Western (wymani) and Yellow-footed (livens). Note that, for Yellow-footed and fuscus, the bird would have to be its first year, as those species mature in three years, not four. However, the marbling on the tertials and greater coverts are inappropriate for a first year bird-- this is a second year bird with a four-year cycle; so we can rule out fuscus and livens.

The pink legs are a strike against Kelp, and possibly against livens. The legs actually appear quite pink, which is best for Slaty-backed and wymani. Let's turn to the tertials. These are highly variable in second year birds. Nevertheless, the rather pale wash to the interior solid areas seem wrong for all except Slaty-backed, but that's a tenuous point. The others are typically more uniform dark in the centers. Likewise, the greater coverts are strikingly pale, with extensive solid whitish areas on the outer feathers. This is expected on Slaty-backed and observed on marinus, typically by second summer. See this page for an example. By the time marinus look like this, they are typically rather worn, more so than this bird. This bird clearly has whitish greater coverts rather early in the winter. That's a big strike against Kelp, Western, and intermedius. The lesser coverts are difficult to discern, so I'll leave those alone. The median coverts are primarily pale with dark subterminal marks. This is wrong for wymani, livens, intermedius, fuscus, and Kelp, some of which usually show more adult gray by their second year as well. Again, Slaty-backed and marinus are the best fits. (For a good Slaty-backed photo with this covert pattern, check out http://fog.ccsf.cc.ca.us/~jmorlan/sbgu2.htm, the first summer bird at the bottom of the page). Finally, the primaries are edged with pale crescents. This is quite unusual in second year and, as far as I know, only regular on Slaty-backed. Western Gulls do not show this even in third year. Marinus may show this when fresh, but not when simultaneously sporting such faded-looking greater coverts.

It'd be nice to see the bill to conclusively rule out marinus. As it turns out, this bird had a thick stubby bill and a dark smudge under the eye, as expected in Slaty-backed. It was photographed on February 5, 1996 in Ventura, CA by Don Desjardin. Copyright 1995.
Here is the full photo. Also, there are other photos of the bird at this page. The California Bird Records Committee (CBRC) has not accepted this record, citing lack of knowledge of the species and the possibility of various hybrids with Glaucous-winged Gull.


For as long as this quiz was up, very few folks took a stab at it. I guess seeing only part of the bird is a bit unnerving. As usual, the correct answer won, but with only a plurality, not a majority. Here are the results:

GUESS # OF VOTES
Slaty-backed Gull (2W) (36% correct) 8
Great Black-backed Gull (2W) 3
Western Gull (2W) 3
Western Gull (3W) 1
Herring Gull (1W) 2
California Gull (1W) 1
Glaucous-winged Gull 1
Thayer's Gull 2
Glaucous-winged x Western Gull (1W) 1