About a week ago Leonard and I discovered a leucistic Canada goose (Branta canadensi) and its mate near our home in Big Valley (Modoc County CA). The two geese appear to be a nesting pair and the leucistic goose seems to be the female. According to my research leucistic geese are rare. Leonard and I do not get too close so as not to disturb them.
Leucistic birds lack melanin (pigment) in some or all of their feathers. Birds have two types of melanin – black and brown. These pigments are produced by birds using enzymes and are deposited in growing feathers by color cells. Depending on where in the process of producing or depositing the pigments a defect occurs, different types of abnormalities occur.
Leucistic birds (and other animals) are not true albinos. True albino birds have white skin, feathers and pink or red eyes (because without pigment in their eyes one can see the blood vessels in the back of the eye). Leucistic birds lack melanin in some or all of their feathers and are sometimes called “partial albinos”, a term that is not technically correct. To further confuse the situation occasionally the melanin is deposited in the feathers in very low concentrations producing a washed-out effect called dilute albinism.
According to David Sibley there are several causes for leucisism:
- inability to produce melanin resulting in no melanin in the entire animal,
- Inability to deposit melanin thus the absence of melanin (color) in some or all feathers.
- lack of one type of melanin therefor an animal with no black or no brown coloration,
- the melanin is not completely oxidized during formation changing the black color to brown or making the brown color faint, or
- partial loss of one or both melanin types yielding less concentrated color in the feathers.
I do not know the cause for this Canada goose’s melanism, but from its appearance I would guess that the goose has lost its ability to deposit melanin in some of its feathers.
If this pair of Canada geese are nesting Leonard and I hope to see their offspring to determine if the leucistic trait is passed on.