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A Great Brak River and Surrounds Community Newspaper

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By Sally Adam Reading recent research describing how certain chameleon species have bones which fluoresce under UV light had us wondering about how other creatures might use that area of the light spectrum. Many species of birds, including perching birds, gulls and parrots, are tetrachromatic, with dedicated cone cells for picking up wavelengths in the ultraviolet (UV) and violet (VS) regions of the light spectrum (300-400nm). How do they use it? UVS vision can be useful for finding and selecting a mate. Birds that do not exhibit plumage differences between the genders in visible wavelengths are sometimes distinguished by the presence of ultraviolet reflective patches on their feathers. Male blue grosbeaks (a North American species) with the brightest UV blue in their plumage are larger, hold the most extensive territories with plenty of prey, and feed their offspring more frequently than other males. In one experiment done on budgies, researchers found that their fancy plumage caused the contrast of color under UV to be 25 times more extreme than in visible light. 78 of 108 bird species studied were found to have UV-colored feathers, and 93% of them have evolved to strategically have their most colorful and reflective plumage on parts of the body that are used in sexual display. UVS vision is also thought to help with navigation, prey identification, and foraging. The waxy surfaces of many fruits and berries reflect UV light that advertise their presence to UVS birds. Useful as UV vision is, the trade-off is the damage done to the birds' DNA by the harmful rays, resulting in their relatively short life-spans. What is still not well understood is how parrots are able to maintain their eyes over their long life-times (often 50 years) while using UV vision. Perhaps there will be some clues there as to how best to treat human diseases of eye degradation.

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