Please help identify. Taken last Friday in St Marys (IOS -UK)

Welcome to the forum Mr Claude.

The bird in your photo is a male Blackbird that has Leucism.

There has been some disagreement in the scientific community about what exactly to call birds with white spots.

Solid white birds with pink eyes everyone agrees are albinistic, and pale birds with normally colored but pale plumage everyone agrees are leucistic. But birds with white patches intermingled with normal plumage have been described with a variety of terms.

Albinism is a genetic mutation that prevents the production of melanin in the body.

Leucism is a genetic mutation that prevents melanin from being deposited normally on feathers.

Scientifically, a bird with white patches is, in fact, leucistic.

Since the white patches on birds have no melanin, birds with these patches have been said to have partial or imperfect albinism.

Albino refers only to things which have two recessive genes and, therefore, no pigment anywhere.

As such, you cannot be 'partial albino' as you do not have both recessive genes.

As leucism is a spectrum between white and normal, any odd white feathers are leucistic. This could be genetic, or indeed possibly from infection/trauma. Leucism is kind of the opposite of melanism.

Therefore the white patches are caused by a defect preventing normal deposition of the melanin. And since leucism is a deposition problem, it makes sense that birds with white patches would be leucistic. Consequently leucism comes in two main varieties — paleness, an equal reduction of melanin in all feathers; and pied, an absence of melanin in some feathers creating white patches.

Interestingly, albinism only applies to an absence of melanin. Since some colors come from other pigments, such as carotenoids, it is possible for a bird to be albinistic and still have color.

Leucism, on the other hand, applies to all pigments. It is also possible for a bird to be completely white and still have melanin in the body. In this case the bird would be considered leucistic and would have dark eyes because the mutation only applies to depositing melanin in the feathers.

Albinistic birds have pink eyes because without melanin in the body, the only color in the eyes comes from the blood vessels behind the eyes.

Typically birds with abnormally white feathers do not survive long because they are so much more visible to predators. Those that do survive may have trouble attracting a mate. Consequently, the mutated genes that cause albinism and leucism are less likely to be passed on to a new generation. If you are ever fortunate enough to see one of these oddly plumaged birds, consider yourself lucky!

Regards Buzzard