Mystery Bird: Leucistic/albino European Herring Gull, Larus argentatus

Looks like a gull. Not a "normal" white-winged as should have pale grey wings, so a leucistic bird. With just the structure to go on the bill is heavy and the forehead is shallowly sloping and wings are longer than tail. The nearest I can get from this posture is either Herring Gull or Great Black-backed Gull. A GBB should have a deep chest and this bird looks slimmer than that so I'll hazard Herring Gull.

Both Iclandic and Glaucous Gull juveniles can have a pure white plumage. Brittany seems to be just off their normal winter range, but not by much.
Of the two, I'd say Glaucous which is a bit tougher looking.

I was under the impression that all juv/imm plumages of Iceland and Glaucous Gulls had some degree of pale brown feathering until attaining adult plumage. In fact they are referred to as "biscuits" in the UK. I had thought about these two but the red eye-ring still suggests Herring to me.

Bill pattern looks like an adult. My impression of the structure is more towards Great Black-backed.

I'm not convinced that the condition would necessarily be described as leucism (pigments reduced resulting in a complete or partial "washout" appearance), and certainly not full albinism (complete absence of all pigmentation), but instead "incomplete albinism" which would involve the absence of pigmentation in the plumage, irises, or skin but not all three.

The primaries on a Glaucous Gull (Larus hyperboreus) meet or slightly exceed the tail when the bird is at rest however the primaries of both the Herring (L. argentatus) and Iceland Gulls (L. glaucoides) are noticeably projected beyond the tail, as seems to be indicated in the photo above.

Glaucous Gulls have big heavy bills, and Iceland Gulls have bills that are shorter and thinner than Herring Gulls- the weight of the bill and the sloped forehead above certainly exclude the Iceland Gull.

The iris is pale, but the orbital ring should provide a more definitive identification since this photo was taken in the breeding season- the Iceland Gull would have a purplish-red ring, the Herring orangish-red, the Glaucous eyering would be bright yellow, the Lesser Black-backed and Great Black-backed would be red...

As for build, I think the bird above is not bulky enough for a Glaucous or a Greater Black-backed but about right for the Herring...

If the legs were yellow I would be tempted to go for a Lesser Black-backed (L. fuscus) or even the newly encroaching Caspians (L. cachinnans), but as they are more pink I'm going to go for the Herring Gull that populates the British Isles/Northern and Western France/Western Germany, Larus argentatus argenteus.

Let's see ... while Glaucous Gulls never show a 'typical' all-white plumage, a 2nd year bird can show just a little barring in out-of the way spots. However, it wouldn't show an adult bill or a breeding-condition orbital ring. In any case, a Glaucous Gull should always show white outer primaries -- in this bird, it appears that the only pigment is actually on the primaries. The same applies to Iceland Gull (the nominate race, at least), and Iceland would have a much smaller bill. Using primary extension on a bird in this position seems a bit risky, but a Glaucous should have short primaries compared to the tail.

So, it looks like a partial albino/extremely leucistic bird. (The gray on the primaries argues against an incomplete albino). I'll agree with David that the leg color seems wrong for L. cachinnans or fuscus, or Yellow-legged Gull, L. micahellis.

That leaves us with Herring Gull or Great Black-backed Gull. The eye color seems closer to Herring Gull, the orbital ring to Great Black-backed. If we assume that the photo was taken late enough that the bird is actually within its breeding range, then the Herring ssp. we expect would be L. a. argenteus. And here's where a close inspection of those primaries comes in. It appears to me that the outermost primary (P10) is entirely white at the tip. This is typical of Great Black-backed, somewhat rare in L. a. argentatus (the northern race of Herring Gull), and not typical of argenteus. In addition, while the bird doesn't appear all that bulky, the bill seems quite large to me.

So, assuming that the bird is actually on its breeding ground, I'll say that this is a Great Black-backed Gull. Of course, I won't be surprised to hear any of several other species.

Paul, a confounding variable here is how "leucism/incomplete albinism" would affect the skin color of the feet if they were yellow- I can't refer directly to the photo from work (flikr is blocked!) but I remember going back and forth over the legs because they were a little off-color- certainly not yellow but not as pink as I would expect from a Herring or Great Black-backed... so if we were to put the leg color on hold for a moment, what would we actually have?

Acknowledging the phylogenetic connection, I would also be tempted to bear in mind the following herpetological terms which would rationalise why eyes and not legs, plumage and not skin, or a number of other combinations out of the ordinary might apply:

Erythrism (Erythristic) - excessive production and deposition, or distribution of red pigments (orange possibly).

Anerythrism/Anerythristic - lack of production of pigments in the darker orange to red range.

Hypoerythrism/Hypoerythristic - reduction in the amount of darker orange to red pigments so that the appearance of this color is largely absent except for traces or appears "washed out."

Xanthism (Xanthic) - excessive production and deposition, or distribution of yellow pigments (orange possibly).

Axanthism/Axanthic - lack of yellow and lighter orange pigments, depending on the point in the pigment cascade, this mutation can also cause corresponding anerythrism since erythric pigments (drosopterins) appear to come from the more yellow pteridines biochemically.

Hypoxanthism/Hypoxanthic - reduction int he amount of yellow or lighter orange pigments so that the appearance of this color is only found in trace amounts or appears "washed out." This may also result in hypoerythrism since the red pigments appear to be made from the yellow pteridines.

Melanism (Melanistic) - excessive producution and deposition, or distribution of melanin pigments (may be orange if pheomelanin to black if eumelanin).
Amelanism/Amelanistic - lack of melanin production. At least three basic forms are possible, though whether all forms have been observed is questionable. 1) amelanism where the chemical cascade is defected before eumelanin and pheomelanins take separate biochemical routes, resulting in a complete lack of melanin production. 2) aeumelanism - where only eumelanin production is blocked. 3) apheomelanism where only production of pheomelanins is blocked.

Hypomelanism/Hypomelanistic - condition resulting in the reduced production of melanins. At least three types are possible by restriction of production at the initial stages of melanin production, at the eumalnin production cascade or at the pheomelanin cascade.

Iridism (Iridistic) - excessive production and deposition, or distribution of iridophore platelets (this is, as yet, only a theoretical condition).

Aniridism/Aniridistic - (again theoretical - I have not heard this reported) lack of the formation of refractile platelets in iridophores.

Hypoiridism/Hypoiridistic - (theoretical) reduction in the number of refractile platelets formed in iridophores.

I'm afraid that herpetology is a field I don't know much about -- apparently the mechanisms underlying pigment variation are better known in reptiles than in birds, or at least than when I was teaching Orn. lab a few years back.

I do know that in birds, it's not particularly rare to find a) birds with partially white plumage, b) birds with largely or entirely white plumage, but normal or at least close to normal bare parts. Complete albinos, with a lack of pigment in the bare parts, are apparently much rarer. Given that the bare parts are often a much different color, and therefore likely involve a different set of pigments, this probably shouldn't be too surprising.

In this case, there appears to be a normal amount of yellows and reds but there is clearly a greatly reduced production of melanins -- melanin only just barely shows in the primaries, normally the darkest part of the bird to begin with.

I've seen a Franklin's Gull in Colorado that showed a somewhat similar condition -- I was sure I had an Ivory Gull until I got the scope on it, and could see a faint shadow of a hood.

Incidentally, with birds you need to add another set of conditions -- I don't know that they have iridophores, but the feathers often show a structural component to their color (Hummingbirds, any bird with blue), and that could hypothetically be missing, or appear in strange spots.

I'm not sure where you draw the line between extreme leucism and partial/incomplete albinism. We in the UK certainly get "black birds" ie corvids and Blackbirds that commonly show some or a lot of white feathering, although completely "white" birds are rare enough to gain a few line in the national papers when someone photographs them. Also do completely albino birds have the red eyes that are seen in mammals?

Just to give the proper attribution, the herp info was from a Veterinary Herpetologist Blog...

I suggested he herp connection because of the phylogenetic implications of the class Aves and it's sister group, the clade Crocodilia, both together being the sole living members of the reptile clade Archosauria.

Thanks for the link, David. How much of that is known from Crocodilia, and how much from lizards and snakes? I ask because at that point the phylogenetic connection is much older.