RARE SIGHT: Bird colouration not always black and white
A reader sent me a photo of a white crow and asked how it could get like that so this week I will explain how an excess or a lack of the pigment melanin can result in black and white birds.
Normal levels of melanin in birds will result in a normal range of colours in their feathers which can range through all colours of the rainbow.
Darker feathers have more melanin than lighter feathers so when there is an excess of melanin the dark feathers and the light feathers can turn black.
This can be seen in the photo of the kookaburra (left) which is nearly all black except for some blue on the wings.
A lack of melanin means that normally dark feathers will turn white as can be seen in the photo of the zebra finch (right).
You will notice that some colours remain so it is not what would be called an albino which happens when there is a total absence of colour and pink eyes.
In the case of the kookaburra it would be said to be melanistic, having an excess of melanin.
In the case of the finch it would be said to be leucistic, having a lack of melanin.
It is quite a rare condition but can happen in a wide range of bird and other animal species including humans.
In birds either condition will cause a difficulty in attracting a mate because they do not look normal and they often get attacked by other birds and many do not survive.
An excess of melanin also makes the feathers quite brittle so that they are damaged more easily and broken wing feathers mean that the bird cannot fly.
Let me know if you have seen a melanistic or leucistic bird and send in a photo if you have one.
Allan Briggs is the secretary of BirdLife Capricornia. Contact him with your bird questions at email@example.com