Vocalizations shape roost defence outcomes in a solitary bat

Individuals commonly compete with others that share their ecological niche, both within and among species. To avoid physical confrontations, individuals can use various types of signals to demonstrate their dominance, including vocalizations. Kerivoula hardwickii is a solitary bat species that roosts in plant structures that are highly ephemeral, making them a limited resource. So far, it is unknown whether individuals of K. hardwickii use vocalizations during competitive encounters for roosts or whether these vocalizations convey information about the roost defender to potential rivals. We hypothesized that the calls produced during roost competition contain information that influences the ability of an individual to defend its roost. We conducted roost competition experiments in a flight cage, where one individual was allowed to take possession of a roost (‘owner’) and a second individual released into the cage (‘intruder’) attempted to evict the owner. All vocalizations produced by the roost owner during these encounters were recorded and analysed to determine which acoustic parameters, if any, influenced the probability that the owner would successfully defend the roost. We found that males that produced calls with higher entropy were more likely to retain their roosts against a male intruder, while there was no such effect in female–female experimental pairs. High entropy suggests that encounters between males of K. hardwickii escalate to high levels of aggressiveness. We suggest that the vocalizations of K. hardwickii contain important information about individual characteristics, which in turn helps bats to make decisions during resource competition.