Heterospecific eavesdropping in a nonsocial species

Many species respond to heterospecific alarm calls, and the majority are social taxa and possess complex alarm calls themselves. Thus, the ability to respond to heterospecific alarm calls may be facilitated by possessing both these traits. Gunther's dik-dik (Madoqua guentheri) is a monogamous, territorial, and nonsocial miniature antelope with a simple vocal repertoire. Dik-diks are highly vulnerable to predation and could benefit from eavesdropping on heterospecific alarm calls. We broadcast recordings of white-bellied go-away bird (Corythaixoides leucogaster) alarm calls to dik-diks to test whether they could respond to heterospecific alarm calls. On hearing a go-away bird alarm call, dik-diks increased their likelihood to run to cover, decreased their foraging activity, increased their rate of head turning, and increased their period of vigilance compared with a nonthreatening bird song. Thus, predation risk alone, in the absence of complex sociality or complex communicative abilities, may be sufficient to drive the evolution of heterospecific eavesdropping.