Leucism

It is hard to walk around Filey and miss the number of leucistic carrion crows that exist within the town, but what is leucism and why does it occur?

Leucism is a genetic mutation which prevents the body producing melanin (black pigment) and accurately depositing it around the body. Where feathers lack melanin they are white/or paler, this can include parts of a feather or entire feathers. Leucism does not always result in feathers being white, sometimes the lack of melanin makes the feather paler giving it a diluted look (some consider this to be a separate condition). Leucism is slightly different to albinism in that it blocks all pigments not just melanin, where as albinism still allows carotenoids to occur giving other colouration i.e. yellow, red. In completely leucistic individuals the entire body is white, but the eye is not red like in albinism, as leucism only affects the feathers. The red eye in albino animals is a result of the eye lacking any melanin, allowing the red blood vessels in the eye to be seen.

Interestingly the condition must be passed down through generations as it has certainly existed in the Filey carrion crow population for a number of years.  Leucistic feathers are thought to wear quicker, and may make some species more prone to predation, although it certainly does not seem to be having a huge impact on these crows. A smaller passerine is perhaps at a greater risk of been seen by a predator. However chances of survival are higher than albino birds, which usually die soon after fledging due to their poor eyesight and increased vulnerability to predators.



Leucistic Carrion Crow