The onset of activity in animals restricted to being active for only part of the day is one of the most fundamental aspects of their biology because it marks the beginning of activities that they need to do to survive and reproduce. Initiation of activity is subject to several factors including presence/absence of predators and the vagaries of environmental conditions at the time of emergence. We tested if the emergence times amongst seven species of sympatric insectivorous bats were explained by predation risk, insect activity and weather conditions. We measured bat emergence times by recording echolocation calls. Peak emergence was correlated with body size, time of sunset, foraging strategy and diet, factors associated with risk of predation. Larger, faster flying bat species emerged earlier than smaller, slower flying species suggesting the former relied on flight speed to avoid predation. Clutter foragers emerged earlier than clutter-edge and open foragers, suggesting that vegetative cover is important for bats trying to avoid predation. Bats feeding on Lepidoptera emerged earlier than bats feeding on Diptera. However, insect peak activity was highly variable and did not differ between orders or time of season. Emergence time was not correlated with any of the weather variables we measured. These results suggest that predation influences fundamental aspects of the biology and ecology of insectivorous bats by determining when it is safe to become active.
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Vol. 15 • No. 1