No, I'm not referring to those of us who don't conform to what is generally accepted as 'normal', but to those of our feathered friends whose colouring doesn't conform to what is 'normal' for them!
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I'm sure many of us have seen such a bird and perhaps wondered about it? I know I have.
My curiosity was aroused after we saw what we thought at first was an immature magpie with unusual markings, which never developed into the traditional magpie colourings. We saw it over a period of three or four years, and even when fully mature the colourings never changed. After some research (via Mr. Google of course!) I discovered the reason for this maggie's unusual colouring - it had leucism.
Leucism is an abnormal plumage condition caused by a genetic mutation that prevents pigment, particularly melanin, from being properly deposited on a bird’s feathers. As a result, the birds do not have the normal, classic plumage colours, and instead the plumage has several colour changes, including: white patches, paler overall plumage, overall white plumage with little or no colour.
The degree of leucism will vary depending on the bird’s genetic makeup. It can affect the plumage only slightly, or in a major way where the plumage is totally white.
Albinism is another genetic condition that can turn a bird’s plumage pale, but there are distinct differences between albino and leucistic birds.
Leucism affects only the bird’s feathers, and typically only those with melanin pigment – usually dark feathers.
A leucistic bird with different colours may show some colours brightly, especially red, orange or yellow, while feathers that should be brown or black are instead pale or white. Some leucistic birds, however, can lose all the pigment in their feathers and are pure white.
Albinism, on the other hand, affects all the pigments, and albino birds show no colour whatsoever in their feathers. Furthermore, an albino mutation also affects the bird’s other pigments in the skin and eyes. Albino birds show pale pink or reddish eyes, legs, feet and a pale bill, while leucistic birds often have normally colored eyes, legs, feet and bills. So, if you see a bird that you think may be an albino, check carefully to see if it is only mostly white, take a good look at the eyes!
Leucistic birds face special challenges in the wild.
Lighter plumage may rob the birds of protective camouflage and make them more vulnerable to predators such as hawks and feral cats. Because plumage colours play an important role in courtship rituals, birds with leucism may be unable to find strong, healthy mates. Melanin is also an important structural component of feathers, and birds with extensive leucism have weaker feathers that will wear out more swiftly, making flight more difficult and eliminating some of the bird’s insulation against harsh conditions.
Melanism is a condition caused by a genetic mutation that gives a bird excess amounts of melanin in its feathers. This makes the feathers much darker than normal plumage, and many melanistic birds appear completely brown or black. There are two ways melanism can affect birds’ plumage: normally dark markings are bolder and overrun their typical boundaries, or all the plumage is darkened.
Just like with leucism, melanism can vary for different birds and some individuals will show much darker plumage than normal, while other birds will have less noticeable changes in their colouration.
Whereas leucism can be dangerous for birds because it robs them of camouflage, melanism can actually be beneficial by helping conceal birds more fully. Of course, a bird with melanism may still have difficulty attracting a mate because their colouration is not the expected breeding plumage. Too much melanin in feathers may also rob the birds of some feather flexibility, which could lead to brittle feathers that are subject to damage more easily.
Birds of course aren't the only creatures to be affected by these conditions – I have used them as an example as they are the wildlife that most of us see on a regular basis. However, if you live in the Northern Territory you may come across 'Pearl' - the leucistic crocodile spotted last November in the Adelaide River!