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Killers at large

The Casade frog ( Rana cascade ) and the Western toad ( Bufo boreas ) are dying, so is the Pacific tree frog. But there is probably no single cause for the dwindling population of these sentinel creatures, says zoologist Andrew Blaustein of the Oregon State University, USA. Increased ultraviolet (UV) radiation is found to be killing the first two, but the tree frog seems to be immune to UV. Other possible reasons for their deaths could be pollutants or infections from pathogens. "If global warming is to blame, it is not obvious now,' says Cynthia Carey of the University of Colorado, USA ( New Scientist , Vol 165, No 2227).

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