Heterospecific alarm call eavesdropping in nonvocal, white-bellied copper-striped skinks, Emoia cyanura

Abstract

Many species benefit from listening to the vocalizations of their predators as well as the alarm vocalizations of other species. This eavesdropping is an important way to acquire information regarding predator location and threat magnitude. Previous studies have investigated lizards eavesdropping on predators, while others have studied lizards eavesdropping on alarm calls. Studies that examine lizard responses to playbacks of both predatory calls and heterospecific alarm calls are absent, even though eavesdropping may be especially important in nonvocal species. By comparing both types of calls, we can assess their relative importance to skinks and understand how skinks discriminate between these calls. We broadcast sympatric predator vocalizations and both alarm call and nonalarm social vocalizations from a nonpredatory bird (red-vented bulbul, Pycnonotus cafer) to determine whether nonvocal, white-bellied copper-striped skinks could discriminate among them. Upon hearing red-vented bulbul alarm calls, white-bellied copper-striped skinks reduced their rate of looking and increased their rate of bloating compared to a baseline period. However, they did not respond significantly to red-vented bulbul social calls or to vocalizations from potential predators. Our study is the first to look at the relative magnitude of response to playbacks of predator and heterospecific vocalizations in lizards. White-bellied copper-striped skinks most likely depend on heterospecific vocalizations for predator information because they are nonvocal and found low on the forest floor, making it harder for them to identify predators directly than through alarm calls of avian heterospecifics.