Shared predators between primate groups and mixed species bird flocks: the potential for forest-wide eavesdropping networks

A basic tenet of animal behavior is that animal groupings (e.g. schools of fishes or flocks of birds) are widely influenced by predators. Many studies have focused on communication between individuals within the same species or different species within a defined social group; but predators typically select from a number of different co-occurring species. To evaluate whether two distantly-related species with similar predators share vocal information regarding predator threats, we conducted a field experiment in the Amazonian rainforest involving an avian prey-species, a primate prey-species and a shared predator. In our reciprocal field experiment, we elicited alarm calls from birds (bluish-slate antshrikes Thamnomanes schistogynus) and primates (saddle-backed tamarins Leontocebus weddelli) by exposing them to a trained raptor (bicolored hawk Accipiter bicolor). We then played all types of recorded alarm calls back to birds and tamarins, and measured 1) the time to respond (for both birds and tamarins), and 2) the distance moved across the substrate (for tamarins). Our results show that both birds and tamarins were significantly more likely to flee when hearing vocal alarms compared to a control (a common bird call, the screaming piha Lipaugus vociferans), regardless of the species who produced the alarm. In addition, tamarins moved significantly more upon hearing bird alarm calls when compared to the control. We suggest that signals regarding shared predators may be highly valued across prey from distinct social groups. These data support the hypothesis that overlapping potential predators can drive communication between distinct prey groups, resulting in taxonomically diverse eavesdropping networks within tropical rainforests.