Interspecific eavesdropping by birds on a keystone mammal improves antipredator behaviour

Abstract

In animal communication networks, keystone information producers generate large volumes of reliable information, which eavesdroppers can use to improve fitness. To better understand how these interactions can shape animal behaviour, we investigated potential eavesdropping between long-billed curlews, Numenius americanus, and black-tailed prairie dogs, Cynomys ludovicianus, a social, colonial keystone species known for their vigilance behaviours and distinct alarm calls for different predator types. We used playback and a simulated predator in paired experiments to test whether prairie dog alarm calls cause curlews to exhibit defensive behaviours sooner, namely when nonincubating males alarm-call and mob and when incubating females adopt cryptic posture on the nest. The median distance of the simulated predator from the nest when the incubating curlew adopted cryptic posture was significantly farther away with prairie dog alarm calls than without alarm calls. However, nonincubating curlews did not show a difference in their alarm-calling or mobbing behaviour in response to prairie dog alarm calls. We infer that incubating curlews eavesdrop on prairie dog alarm calls to improve nest defence, and we suggest that black-tailed prairie dogs are keystone information producers, which has not been widely recognized as one of their keystone effects. Reduced predation risk via eavesdropping could explain why animals associate with prairie dog towns despite high levels of predator activity. These findings emphasize the need to better incorporate keystone information producers into conservation efforts because they provide unique ecological benefits that cannot be replicated otherwise.