Albatrossity2
Posts: 2780
Joined: Mar. 2007
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| Quote (dhogaza @ May 22 2010,16:33) | Interesting note from the Cornell:
| Quote | | occasionally a bird will lose feathers in a close call with a predator. When this happens the new feathers sometimes grow in white and then change back to the normal color at the next regular molt. This kind of white coloring looks like leucism but is not. |
Interesting ... I was triggered to look by doubting that the cause of apparent partial (pied) leucism is always genetic (i.e. "is it a mutant?"), just because it seems reasonable that physical damage could harm follicles and sometimes lead to a lack of melanin.
Hmmm I guess it's accurate to say that all true leucism is genetic (Cornell says so), but not all birds possessing some unusual white feathers are truly leucistic.
BTW, perhaps the most beautiful red-tail I've seen in the hand was a "pale leucistic" (overall off-white rather than splotches of white intermixed with normal plumage) one. It was the color of milk with a few drops of coffee ... a very pale off-white hinting brown.
So now, after identifying the species, our poster needs to follow the bird around until it molts to see if they come back colored or white! :) |
Another cause of the aberrant white feather or two is a local infection/inflammation while the feather is growing. Just like the melanin-forming pathway in cats, apparently there is a temperature-sensitive step in melanin formation in birds. A local hot spot on the skin can denature tyrosinase and result in a white feather growing from that spot. Ticks or other ectoparasites can cause these local inflammatory responses. I've seen numerous examples of white feathers in Common Grackles that I've banded, and I suspect most of them arise via this mechanism.
And these will grow out with the regular pigment after the next molt, so it's a temporary aberration.
For those interested, I published a short note about aberrant white feathers in wrens in the Bulletin of the Kansas Ornithological Society in 2002. Apparently leucistic wrens are only rarely reported in the literature.
No updates from me for a while; I'm heading to the Amazon (Manaus and upstream) tomorrow, and will be there for a couple of weeks.
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Flesh of the sky, child of the sky, the mind
Has been obligated from the beginning
To create an ordered universe
As the only possible proof of its own inheritance.
- Pattiann Rogers
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