Albinism among birds is not uncommon but the British Trust for Ornithology is appealing for sightings for its own research, writes ELIZABETH EDWARDS

Reports of sightings of birds with variations in colour are always received with interest, both by scientists and ornithologists. One variation most often seen is albinism and in Oxfordshire affected species such as blackbirds are seen quite frequently.

Albinism can show itself to a greater or lesser extent. Often it is just one or two white feathers, even appearing just as white spots. Other birds may have a completely white section of feathers, such as on the wing or on the head or neck.

This colouring can be dangerous for a bird, for it makes it more visible to a predator.

It can also cause alarm to birdwatchers, for an albino is equally conspicuous by its absence, raising fears for its safety.

The British Trust for Ornithology has carried out studies into the causes of the condition, which is found in a number of species, including sparrows and carrion crows and also in other forms of wildlife. There can be examples of white hedgehogs.

The causes include genetic mutation, dietry deficiency, stress, injury and damage to the gland through which the pigment passes to the feather. A completely albino blackbird would have pink eyes and legs, feet and beak of pink or yellow-white. It is the bird in which albinism is most seen.

The amount of white colouring in white albinos can increase with age. It can also appear in a matching symmetrical pattern, for example in the same feathers on both wings.

An interesting observation relating to blackbirds is that it is most usually the males that are affected by albinism. It may be that the contrast with their black plumage is more noticeable than it would be in the lighter, more brownish colour of the female.

Another cause of white or very pale colouring is leucism, a condition in which the birds lack pigment in the pigment cells.

A condition which has the opposite effect is melanism, where an excess of melanin results in the appearance of a black rabbit or a black squirrel, instead of their normal grey. Birds affected include the bullfinch and the collared dove.

Melanin is also what gives your skin colour when exposed to the sun, your sun tan and freckles.

This, though, is less common than albinism in birds. The BTO has a list of 26 species affected, including the wren and the sparrowhawk but only of nine affected by melanism.

The trust would be interested to hear of any sightings of female albino blackbirds. It can be contacted on 01842 750050 or by email at gbw@bto.org.