Do mule deer respond to the sounds of their predators?

Abstract

Many, but not all, animals respond to the sounds of their predators to assess predation risk. For those that can, does this ability persist after a predator has gone extinct? Are all predatory species equally likely to generate antipredator responses? And, more generally, what are the proximate mechanisms underlying these responses? We reviewed the literature to draw generalizations about predator discrimination abilities and found that prey broadly are responsive to the sounds of both familiar and unfamilar predators, that most of the predators used are birds and mammals, and that responses may require experience, but that some species appear predisposed to respond to certain types of predators. Given that ungulates face risks from a variety of predators, predator discrimination abilities in relatively few species of ungulates have been studied. We then asked whether mule deer (Odocoileus hemionus) possessed the ability to discriminate between predator vocalizations by broadcasting the sounds of coyotes (Canis latrans), mountain lions (Puma concolor), and locally extinct wolves (Canis lupis), as well as the song of novel non-predatory pied butcherbirds (Cracticus nigrogularis). We compared the difference in the proportion of time allocated to heightened responses (the sum of time allocated to alarm walk, stott, run, and stand- look) following playback compared to before playback. Mule deer both respond to predatory sounds, and discriminate among predators. This response was influenced by the familiarity to humans: deer greater than 0.5 km from human residences allocated more time to heightened responses both before and after stimulus playback. Taken together, we found that mule deer can respond to the sounds of some of their vocal predators, and retain an ability to respond to extinct wolves.