Mystery Gull. 26 June 2011 at Newport, Oregon by Chet Conklin.
Every summer a few very white gulls--similar to the one photographed above and sent to me by Chet Conklin--show up and really confuse birders. [Thank you, Chet, for allowing me to use your photos.]
Gulls like this with a bit more pink on the bill are often reported as first-year Glaucous Gulls on the West Coast in summer. But with the dark bill, one may be tempted to match this with an illustration of a juvenile Iceland Gull!
This is not a Glaucous Gull nor is it an Iceland Gull. Here is why.
Ignore the bright white feather color for a minute and look at other field marks, especially shape. This fairly stocky gull has wings that extend barely beyond the tail (it is “short-winged”). The eye is dark, but I do see a paler iris than pupil in one photo. The forehead is rather flat and sloping. Legs and feet are pink. The bill is nearly entirely black, with pink gape (the corners of the mouth on the face) and a bit of paleness at the base of the lower mandible. The bill is heavy and thick, “swollen” at the gonys (where the red spot would be on the lower mandible, if this was an adult of one of the larger species of gulls). The bill is strongly hooked.
The body shape of Iceland Gull is long and thin, with long wings. The bill is small and petite on Iceland Gull, and doesn’t show such a strong hook. The head should be quite round. The Iceland Gull as a whole is “petite.” The bird in the photo is stocky.
The body shape is all right for Glaucous Gull, but the bill is wrong. The bill of Glaucous Gull is stout, but not overly wide at the gonys. The bill shape is not a good fit. More importantly, the bill of young Glaucous Gull is 3/4 to 4/5 pink with the outer 1/4 (or 1/5) of the bill sharply black.
Now go back to the color. Only the Ivory Gull is this all-over-white in normal plumage. Other white gulls will show darker gray or brown bars on the body plumage. So this gull is not in “normal” plumage.
One condition that could explain the white coloration is leucism, a condition where the feathers are unnaturally pale or even white. This is not albinism, as that condition is the lack of all color, which would include pale legs and bill, with an eye with a colorless iris—blood in the vessels making the eye appear pink. I learned recently it was incorrect to call a bird a “partial albino.” But this bird is not leucistic, either, as a close examination of the feathers will reveal.
Take a look at the top photo. Click it to bring up a larger view. Can you make out any nice-looking individual feathers?
Not really. The feathers are shaggy and many look more like hair. This bird is extremely worn. The feather vanes are mostly worn away and only the feather shafts remain. White feathers are weaker than dark feathers; they wear away more quickly. Even though this bird did get new head and breast feathers in April or May, this bird is in desperate need of new feathers again. But it’s not going to get any soon. Gulls go through a complete molt of all their feathers in fall, September through November.
Because this bird has a mostly black bill, we can say it was hatched 1 year ago, probably June 2010. After a few weeks in a downy state, it grew its first set of feathers. But juvenile birds do NOT turn around and molt right away again in the fall. Thus it keeps its first feathers (wing and tail) for over a year. (Body feathers—head, neck, breast, belly, back—are replaced also in spring.) Such one-year old gulls can become very worn and sun-bleached by summer—especially the wings and tail. Thus, this is a very worn and bleached gull.
Now that we know this vital piece of information we can go on to ask: "what species is this?" Well, the angled head and “monster” bill, as well as short wings and stocky body, point to the common West Coast gulls: Glaucous-winged Gull or Western Gull. Since the bird is so pale and worn—and paler feathers wear faster than dark feathers—we can say that this bird was originally quite pale. That makes this a first cycle Glaucous-winged Gull (some plumage descriptions of the past may call this a “first summer” plumage, in the sequence of downy, juvenile, first-winter, first-summer, second-winter, etc. until it becomes an adult in the 4th winter).
As noted earlier, many Glaucous-winged Gulls of this age have a much paler pink base to the bill (though uneven) and are reported as Glaucous Gulls.
There. More, I’m sure, than you ever wanted to know.
But in case you're not satiated yet, here is more:
A previous post on Glaucous-winged Gulls.
My pBase photo album images of Glaucous-winged Gulls.