THE USE OF CHEMICAL CUES IN PREDATOR RECOGNITION BY WESTERN TOAD TADPOLES

Western toad, Bufo boreas, tadpoles were collected from a lake in the Cascade Mountains of central Oregon, where they occur in sympatry with backswimmers, Notonecta spp., giant waterbugs, Lethocerus americanus, common garter snakes, Thamnophis sirtalis, roughskin newts, Taricha g ranulosa and rainbow trout, Oncorhynchus mykiss. Backswimmers, waterbu gs and snakes prey on toad tadpoles. Newts and trout are potential tad pole predators, but they find toad tadpoles unpalatable. In laboratory tests. groups of tadpoles responded with anti-predator behaviour when exposed to live backswimmers, waterbugs and snakes, but not when expo sed to either newts or trout. In subsequent tests, when only chemical cues from the stimulus animals were presented, the toad tadpoles again responded to backswimmers, waterbugs and snakes, but not to either ne wts or trout. When tests were conducted using only visual cues, tadpol es did not respond with anti-predator behaviour to any of the heterosp ecifics with the possible exception of garter snakes. These results sh ow that western toad tadpoles can distinguish between predatory and no n-predatory heterospecifics with which they co-occur, and that predato r recognition by toad tadpoles is primarily based on chemical cues. (C ) 1996 The Association for the Study of Animal Behaviour