EVOLUTION OF NOCTURNALITY IN BATS - POTENTIAL COMPETITORS AND PREDATORS DURING THEIR EARLY HISTORY

Despite their taxonomic and ecological diversity, modem bats (Order Ch iroptera) are almost exclusively nocturnal. This behaviour is too ubiq uitous to be explained by common patterns of temporal variation in ava ilability of their diverse food sources or by the risk of hyperthermia when flying during the day. Other explanations For bat nocturnality i nclude competition and increased predation risk from birds during the day. In the early and mid Eocene, the known bat fauna consisted of sev eral insectivorous species of sizes similar to those of the modern Eur opean assemblage. This fauna was contemporaneous with several species of predatory birds, including owls (Strigiformes), hawks (Accipitridae ), falcons (Falconidae) and rollers (Coraciiformes), which were the sa me size as modern predators on bats. Predation risk could therefore ha ve been a significant Factor preventing the early bats from becoming d iurnal. Competition from aerial insectivorous birds, however, was less likely to have been significant for bats during the early Eocene, sin ce very few such groups, mainly small Aegialornithidae, were present, with most of the major groups of aerial insectivores evolving later.