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Description
Communication calls serve multiple purposes in the animal kingdom, with alarm calls playing a vital role in warning group members about imminent dangers. These alarm calls are prevalent in various animal species, especially among mammalian societies, and provide valuable insights into the study of social complexity and group coordination. Despite the wide range of predators bats encounter, research on alarm calls in the order Chiroptera (bats) remains limited. Fruit bats, belonging to the diverse family Pteropodidae, exhibit a complex social lifestyle across variations in their habitats, body sizes, and foraging strategies. Our study focuses on the Mauritian flying foxes (Pteropus niger), which are an endemic species of fruit bat found in Mauritius Island. These bats have evolved in a non-predatory environment due to the absence of natural predators on the island. This unique setting provides an opportunity to explore the role and development of alarm calls under such conditions. During our fieldwork on the island, we made unexpected observations of a distinct type of call and behavior displayed by the bats when confronted a person entering their captive colony holding a net, which we hypothesize to be associated with impending danger. However, upon conducting extensive observations and recordings in the captive colony and in a wild colony for comparison, we did not detect these calls during inter-colony communication. To further investigate this behavior, we conducted an experiment involving an experimenter entering the captive colony with and without a net, as well as other tested stimuli such as food, loud noise, and "predator-like animals". The results of the experiment revealed notable differences. The bats emitted calls at higher rate and higher amplitudes when the experimenter entered with a net compared to the other stimuli. Furthermore, we conducted the same experiment during nighttime to compare the bats behavior and vocal signals between their nocturnal activity and their diurnal mainly rest period. Surprisingly, the bats called less frequently and at lower amplitudes during nighttime as oppose to daytime. They reacted by flying and moving away in the colony to avoid the net in contrast to the daytime experiment when they rarely flew away. Furthermore, their normal behavior remained relatively unchanged when the experimenter entered without a net, or with the other stimuli that were tested in the second experiment during nighttime. Furthermore, their normal behavior remained relatively unchanged when the experimenter entered without a net or with the other tested stimuli during nighttime. This comparison enhances our understanding of potential variations in their communication patterns, revealing the dynamic nature of their behavior across different time periods. To assess the influence of social factors, we conducted tests in which bats were isolated from their colony and exposed to the same conditions and stimuli. However, alarm calls were not emitted during these tests, suggesting a strong social component in this behavior. Preliminary analysis of our data suggests that these calls serve as alarm calls, to alert and protect colony members, particularly during the less active and more vulnerable daytime.
