Insular tammar wallabies (Macropus eugenii) respond to visual but not acoustic cues from predators

Abstract

We studied the way in which a population of tammar wallabies (Macropus eugenii), which have been isolated from mammalian predators since the last ice age, responded to the sight and sound of historical and ontogenetically and evolutionarily novel predators. Tammars were shown a range of visual stimuli, including taxidermic mounts of two evolutionarily novel predators, a red fox (Vulpes vulpes) and a cat (Felis catus), and a model of an extinct predator, the thylacine (Thylacinus cynocephalus). Controls were a conspecific, the cart on which all mounts were presented, and blank trials in which spontaneous change in behavior was measured. We played back recorded sounds to characterize responses to acoustic cues from predators and to a putative conspecific antipredator signal. Treatments included the howls of dingoes (Canis lupus dingo), an evolutionarily novel predator; calls of a wedge-tailed eagle (Aquila audax), a historical and current predator; and wallaby foot thumps. Controls were the song of an Australian magpie (Gymnorhina tibicen) and a blank trial. After seeing a fox, wallabies thumped their hind feet in alarm, suppressed foraging, and increased looking. The sight of a cat similarly suppressed foraging and increased looking. The sounds of predators did not influence responsiveness, but wallabies foraged less and looked more after thump playbacks. Our results suggest that tammars respond to the sight, but not the sounds, of predators. In contrast, the response to foot thumps demonstrates that this particular sound functions as an antipredator signal. We suggest that responsiveness to visual cues has been preserved under relaxed selection because predator morphology is convergent, but vocalizations are not.