Plumage Abnormalities in Birds
20th February 2023
Many of us who feed garden birds will have observed over the years birds visiting feeders showing unusual plumage. Some species such as House Sparrows and Blackbirds are prone to aberrant plumage, but it can occur in a range of species including birds of prey and waders. Whilst there is a view that many of these species will struggle, many survive for years as in the case of some long-distance migrants, they will return to the same areas for years. We refer to these birds as Albino, Leucistic, or Melanistic. An albino results from a genetic mutation and the lack of an enzyme essential to produce melanin – its eyes are usually red or pink, with flesh-coloured bills and legs. There is no such thing as a partial albino and they are best described as leucistic. Leucistic birds can produce melanin but are unable to deposit it in their feathers so might show patches of white or paler colours – however they will have normal coloured legs and eyes. Melanistic birds have an abnormal amount of dark melanin pigmentation and appear dark brown or black – some species have a dark variant but examples are extremely rare.
A white Great Northern Diver was found by Ronnie Dyer at Arisaig in January 2015. Though photographs were obtained, they were not close views. What appears to be the same bird visited Mallaig Harbour just a few weeks ago where it was photographed by Stephen MacDonald. The image clearly shows a bird with a red eye, pale bill and legs and can be truly regarded as an albino. Great Northern Divers are winter visitors to our area from Iceland, Greenland and Arctic Canada. Coincidentally a similar bird was recorded at a lake in Iceland last June. If it’s the same bird, its surviving well, migrating long distances and is clearly able to see well enough to feed.