We recently had a report at the nature centre, from a local birder, that an American Robin had discoloration throughout its plumage, appearing nearly white. The robin had a normal bill, eye and leg colour but its body appeared almost white except for a few dark feathers in the wings.
The initial thought was, "an Albino robin". But when we investigated further we found there are several species of animals and birds that have a condition called Leucism (also spelled leukism).
So to explain what leucism is we have to start with "what is and what causes albinism". A little confusing but bear with me (or is it bare with me). Okay, that is for another blog.
Albinism is a rare, genetic mutation with a complete absence of (or very little) melanin production. Melanin is a natural pigment in the skin, hair, eyes and even brain tissue. The type and amount of melanin in animals determine the colour of the skin, hair and eyes. With the lack of melanin production albinos have white or pinkish coloured skin and red eyes due to the underlying blood vessels showing through from behind the eyes.
With leucism there is only a partial loss of melanin production and/or distribution. The animal can have white or patchy coloured skin, hair and/or feathers. The pigment cells in the eyes, legs and bills of birds, however, are not affected.
Birds that have this condition face many challenges from courtship rituals to lack of protective camouflage. With lighter colouring throughout their feathers, they are more vulnerable to predators, making them stand out and become easier targets. Without the proper colouring, birds may not find healthy mates. Melanin is also a structural component of feathers, making them strong and durable. So with the absence of melanin, the feathers are much weaker, making flight more difficult and limiting insulation against harsh climates.
In conversation with Bob, he mentioned that Leucistic robins, blackbirds and even chickadees are often observed in our area.
"There is a pure white Red-winged Blackbird at
Matchedash Bay and has been there since
early spring and is doing fine. I know it is often
said that these cases are more subject to predation
but I am not sure that is always the case. There
have been reports every autumn of at least one
pure white moose cow or calf."
So next time you are out birding and you see a bird with unusual white patches or completely white try to see if the eyes, legs and bill are normal. You will then know if you are looking at an albino or a bird with leucism.
American Robin with a condition known as leucism