Mule deer (Odocoileus hemionus) respond to yellow-bellied marmot (Marmota flaviventris) alarm calls

Abstract

Individuals may obtain valuable information about the presence of predators by eavesdropping on heterospecific alarm signals. While playback studies have demonstrated that similarly-sized and taxonomically-related species may respond to the calls of each other, less work has been done to define the boundaries of eavesdropping. In theory, individuals should respond to calls from any species that provide information about the presence of important predators, regardless of body size and taxonomic relationship, however size is often associated with vulnerability. Coyotes (Canis latrans) in the Rocky Mountains prey upon both mule deer (Odocoileus hemionus) and yellow-bellied marmots (Marmota flaviventris), which differ considerably in size, alarm vocalizations, and antipredator behavior. We conducted a playback experiment to see if deer discriminated between marmot alarm calls and the song of a common sympatric bird. We found that deer increased vigilance significantly more after hearing a broadcast marmot alarm call compared to the bird song. Interestingly, deer that were studied within 0.5 km of homes showed significantly greater discrimination than those studied farther from humans. Our results suggest relative size differences do not prevent interspecific communication and that common predators should generally drive the evolution of the ability to learn to respond to meaningful risk cues. As long as two species share a predator, it should benefit the other to respond to its alarm calls.