Timber rattlesnakes (Crotalus horridus) use chemical cues to select ambush sites.

Chemicals left by organisms moving through the environment are used by other organisms to mediate interspecific interactions. Most studies of chemical eavesdropping focus on prey responding to chemical cues from predators, despite the fact that chemical cues are frequently used by predators as a source of information about prey. Crotalus horridus uses a foraging strategy that is widespread among sedentary predators: the snake chooses a site where it is likely to encounter prey and remains immobile for many hours. I investigated this ambush hunting behavior in captive-raised timber rattlesnakes and provide evidence that sit-and-wait predators may discriminate among prey chemical cues, even when they have no prior experience with the prey. Snakes explored chemical cues with chemosensory behaviors, and more frequently adopted a stereotyped ambush foraging posture toward chemical cues from prey sympatric with their population of origin than either allopatric prey or sympatric nonprey species that are eaten by other viperids. These results support the notion that intra- and interspecific variation in diet may be mediated proximally by innate recognition of cues from particular prey items. This system also describes a bioassay that may be used in the isolation and identification of prey-derived kairomones. Studies such as this can be used to determine more realistic parameters for models of predator-prey interaction and foraging behavior that involve secretive, less active predators.