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The eyes have it

May 1, 2019

A recent blog described the appearance of an unusually coloured bird in the neighbourhood, a pink and white Sulphur-crested Cockatoo, the colouring of which had a number of possible explanations. This week another oddity turned up – a black and white Common Blackbird (Turdus merula), see pictures left and below right. The reason for this colouring is more easily explained.

This bird is leucistic (from the Greek word leukos meaning white). Leucism is a condition where an animal has a partial loss of pigmentation causing white patchily coloured skin, hair or feathers. It is debatable whether the condition is a mutation or is caused by a disruption to the development of pigmentation during growth.

Leucism is different from albinism which is the absence of melanin, a natural pigment found in most organisms. As well as an absence of colour in the skin, hair or feathers albinos also characteristically have no pigmentation in their eyes. The eyes therefore tend to look pink or red which is the colour of the blood vessels within. Leucism does not affect eye colour.

The Blackbird clearly has dark eyes as has the leucistic magpie (pictured left) previously reported.

If I next see a pink elephant in the street I’ll be sure to check out the eyes to determine the cause of its colouration. I’ll also give up alcohol.

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