albinism vs leucism

 

Both birds are Canadian geese, but why is one of them white?  It happens because of a loss of pigment and is attributable to either albinism or leucism.  Which one is it, and what's the difference?

Albinism is a term most are familiar with because of pet mice, rats, and rabbits.  The gene that codes for melanin, a pigment in the skin, hair, and eyes that produces colour, is faulty and either is not transcripted at all or, if it is, does not cause a change in colour.  Albino birds are stark white and have yellow, or at the least, very light coloured bills and legs.  Unlike the mice noted above, birds with albinism have dark eyes, although they may be lighter than a bird without the condition.

Leucism is a condition where there is a reduction in pigment in part or all of the organism.  Leucistic birds have dark eyes, bills, and legs.  They may have patches of white or may be white throughout.  Birds with patches of white are sometimes called pied or piebald.  The cause of leucism is uncertain.  Some sources say that it is genetic in nature while other sources attribute the condition to an error in embryo development.  

It turns out that feathers devoid of melanin are more brittle and easily damaged.  The pigment makes the feather more resistant to abrasion.  This is why many gulls have black wing tips.  

The white Canadian goose in the photo is leucistic because the bill is black and there is some pigment (tail, cheek patch) present.  If you want to see images comparing albino and leucistic birds, click here.

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