Heterospecific nonalarm vocalizations enhance risk assessment in common mynas

Animals rely on their acoustic environments to gain information regarding predator threats and social opportunities. However, because individuals have limited attention, focusing on a particular aspect of their acoustic environment may affect their ability to allocate attention elsewhere. Some previous studies support the distracted prey hypothesis, which suggests that animals may be distracted by any stimuli, inhibiting their ability to detect approaching predators. In this study, we further tested the distracted prey hypothesis by employing playback experiments to simultaneously examine the relative effects of 3 types of noises—anthropogenic sounds, conspecific nonalarm sounds, and heterospecific nonalarm sounds—as distractors for common mynas (Acridotheres tristis). We used 3 different stimuli: motorcycle noise, social common myna calls, and social red-vented bulbul (Pycnonotus cafer) calls. We first examined myna response to each stimulus by measuring time allocation to various behaviors immediately before and during broadcasting the 3 playbacks. We then studied how these stimuli affected their antipredator behavior by measuring the distance at which they fled from an approaching predator (flight initiation distance). We found that mynas responded to all 3 stimuli by delaying their return to relaxed behavior following the playbacks compared with a silent treatment. In contrast to the distracted prey hypothesis, we found that mynas fled at greater distances when hearing red-vented bulbul social vocalizations than during our silent treatment. This suggests that rather than distracting, some social vocalizations may enhance prey vigilance and lead to earlier flight.