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Hint: The dark bird in the top photo is a juvenile Herring Gull (smithsonianus).

ANSWER: The correct answer is Herring Gull, a juvenile leucistic or schizochroistic smithsonianus Herring Gull to be exact.

Right off the bat we see it's a pale-winged gull, which seemingly narrows the field down to Glaucous, Iceland, and Glaucous-winged Gulls. But something is amiss. The primaries, secondaries, and rectrices are too dark relative to the rest of the bird. We may expect a tail this dark on Glaucous-winged, but not combined with such a pale body. This suggests a possible hybrid between a pale-winged species and a dark-winged species.

But hold on; more is amiss. The overall body is exceptionally pale (even white) with fawn tones and a lack of any barring on the coverts. Because the bird has a fairly dark bill and no sign of adult gray on the mantle, it appears to be a first-year bird (possibly second-year). This plumage that doesn't fit any species, combined with the fawn tones and degree of paleness we wouldn't expect in any hybrid, should cause us to suspect this is a bird with a feather pigmentation abnormality. It appears faded, diluted, washed-out, with only some strange fawn-tan tones coming through. This abnormality, called schizochroism, is fairly common in birds. Note that the soft parts appear somewhat normal, although the basal two-thirds of the bill are not as black as the tip (which is also wrong for a normal Glaucous-winged Gull).

With a bird like this, we cannot trust the plumage very much. If we rely solely on structure (including bill shape), the bird appears identical to the juvenile Herring Gull next to it. Could they be siblings? Returning to what we can see of the plumage, it is consistent with a faded juvenile or first year Herring Gull, with relatively darker remiges and some pale barring at the base of the outer rectrices (which is rarely present on Glaucous-winged). Using these clues, it's probably safe to assume the bird is a juvenile Herring Gull like its neighbor.

Terminology regarding plumage abnormalities is hardly a settled affair. Here is my understanding:

Albino refers to an animal which has a complete lack of the cells that produce pigments and thus has no pigment anywhere. This is caused by two recessive genes. Such birds would be completely white with pink eyes and pale pink legs. They are very rare.

Partial albino is somewhat of an ad hoc term. Some would say there is no such thing and that such birds are leucistic (or partially leucistic). However, the term is often used for birds with white patches, where certain feathers (ranging from one to a whole group) are white.

Leucistic is a genetic mutation in which a bird has lost all pigmentation (i.e. is white) on one feather (thus, covering "partial albinos", but is technically "partial leucism") to all feathers, but normally colored soft parts. However, the term is often used incorrectly for pale, washed out birds where the coloring is diluted (as with the quiz bird) (called "dilution" by bird breeders).

Schizochroism is technically the correct term for faded or diluted birds, being a loss or dilution of only some pigments, but allowing other pigments to remain. For example, melanic schizochroism occurs when there is a loss of the phaeomelanins (the browns) resulting in a more uniformly gray bird, or the loss of the eumelanins (the dark browns or blacks) resulting in an all tan or "fawn" colored bird. Bird breeders refer to these as "greyinos" and "creaminos", respectively.

Our quiz bird appears to be a creamino, or schizochroistic.

This bird was photographed August 2, 2005 along the Kenai River, Alaska, by Randall Davis.

Herring Gull 24 (38% correct)
Iceland Gull (Kumlien's or glaucoides) 15
Glaucous Gull 7
Herring x Glaucous Gull 4
Glaucous-winged Gull 3
Thayer's Gull 2
Glaucous x Glaucous-winged Gull 2
Glaucous x Slaty-backed Gull 1
Glaucous x Thayer's Gull 1
Thayer's x Kumlien's intergrade Gull 1
Ivory Gull 1
Laughing Gull 1
Red-legged Kittiwake 1