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Just before I caught the flight home to the UK from Phoenix I sent a photo of a partial-albino Cactus Wren I'd photographed the day before at Papago Park to the very popular Birds-Pix Yahoo group.
I had hoped that it might be interesting to its members, but instead I seemed to have caused quite a debate over my use of the term "part albino" in the subject bar. Can you have a "part" albino?, asked one member. Surely, he means 'leucistic', said another...Well, yes you can, and no I didn't: and here's why.
Firstly, what is "albinism"? Simply put, albinism is a genetic aberration where there is a total absence of pigment in the plumage and/or bare-parts. An "albino" bird therefore is one with no pigment whatsoever: it will have totally white feathers, and it will have a pink bill and legs, and pink or red eyes, caused by the blood supply under the pigmentless skin being visible.
Secondly, what is "leucism"? Scientists and aviculturalists use the term slightly differently, but in essence "leucism" is a partial loss of pigment which affects all of the colours present and 'dilutes' their intensity. Colours and associated plumage marks are still present, therefore, but are washed-out.
This dilution or washed-out appearance can be caused by another aberration called "schizochroism". Here, though, one or more specific pigments (perhaps red or green) is missing: every other pigment is present at normal levels, but where a dominant colouration is lost this can result in the bird looking abnormally "pale" (if the dominant colour was black, and the genes for creating black pigment is faulty, then the bird will have white feathers instead of black ones, but will still more than likely have normally-coloured bare parts).
So, on to the bird that sparked this discussion. The Cactus Wren here has white patches scattered throughout its plumage, but does have normal - not 'diluted' or washed-out - colour in eg the folded primaries and in the retrices (tail feathers). It has no pigment in the bill or legs, but does appear to have a normally coloured eye - though because of the rich blood supply to the eye "full albinos" often appear to have dark eyes.
Clearly, this is not an "albino" and is not "leucistic": but is it a partial albino - after all many birds have the odd white feather or feather tracts? If the bare parts had been normally coloured, then the Wren could possibly have been described as just "aberrant" (though to an unusual degree), the loss of colour in the feathers perhaps (?) caused by illness or stress and therefore perhaps temporary: but as the bare parts are mostly pigmentless as well I do feel justified in using the term "partial albino" - in this case the loss of colour is genetically-based and permanent (ie moulted colourless feathers will always grow back white).
It's interesting to speculate just how long an abnormally coloured bird like this one might survive in the wild - on the one hand the mottled colour makes it stand out (and therefore easier for a hawk or cat to see) against the dry brush, but on the other it disappears in the broken sunlight/shade under a bush and looks disconcertingly 'shapeless' when running along the ground...
I've posted a Gallery of Cactus Wren photographs taken in Mexico and California, with two more photos of this unusual bird at Cactus Wrens
There's also an interesting discussion on the wonderful MilkRiverBlog at milkriver.blogspot.com/2005/03/env-albinism.html
And I'd like to thank Diane from Arizona who mailed me in Jan 2007 with the following - note in particular how long she has been seeing her part-albino Cactus Wren:
"I was pleased to find the excellent photos of the white cactus wren on your website. I have been seeing a white bird at the same spot in my neighborhood for more than three years, and it has taken a while to get a close look at it. Well, I finally got within about four feet of it today to confirm my suspicions that it was a cactus wren. I also confirmed that it was not entirely an albino because it has a dark eye. It has fewer gray feathers than the one in your photo, but they look quite similar. It was hanging around with a normally pigmented cactus wren, which I have seen do it over the years. I read once about a subspecies of cactus wren “San Diego” that is lighter, but this bird is almost completely white."
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