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Index of Subjects
Index of Subjects Quoting Eric Mills: "To save a lot of memory work, I suggest "pigmentally-challenged" (politically-correct, and maybe attention-getting too) for anomalously coloured birds, followed by a short description of what they look like." Hah, friend Eric, I agree that the terminology is arcane and unnecessary in everyday parlance, but I do like to tease. Also, when trying to unravel CAUSES, it's sometimes useful to use precise terms. Take this Blue Jay currently at feeders of Fern McCuish in Hammonds Plains, HRM, photo'd by her recemntly, and the photo forwarded to me by Ken McKenna. You can see this bird under "other passerines" in NS-RBA photos if you're signed up. The bird has white (not normal gray) flanks and a lovely pale blue mantle and head, with no black markings on the head. But the feathers are wispy and frayed and it doesn't look very sleek at all in those parts. Yet its flight feathers are all sleek-looking and barred with black, as in normal birds. So, it's PARTIALLY ANEUMELANISTIC - so there! The bird lacks black EUMELANIN in those CONTOUR (body) FEATHERS that normally have small amounts to darken the white flanks and deepen the blue of the back. Why is that a problem? Trouble is that feathers that have melanin need it to help strengthen the feathers against wear - otherwise they they get frayed and messy, like our jay's (and like the faded wingtips of gulls before they molt in summer). It may be even worse if those feathers are STRUCTURALLY COLOURED, like all blue feathers in birds. These have open spaces in the feathers that refract and reflect light to produce the colours seen. Melanin particles may help modify the tone of these colours, and also strengthen the feathers. Because of their open structure, these feathers are very wimpy without melanin -hence our messy blue jay. Note on the photo of the Blue Jay that the feathers along the middle of its breast and belly seem more slick. But they never did have melanin - nicely white in normal birds - and are presumably constructed more robustly without depending on melanins. So, why wasn't our House Sparrow equally messy. Remember that sparrows have no structural colour (only brown and black pigments), so their feathers may not be as weak as the blue ones of the Blue Jay, and this individual retained its PHAEOMELANINS that may have given enough strength to its feathers. Thus endeth the perfectly useless lesson - possibly of mild interest to some (and really a working out of my own partial understanding of the issue). Cheers, Ian Ian McLaren
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Index of Subjects