Foraging strategy and predation risk as factors influencing emergence time in echolocating bats

Abstract

We hypothesized that interspecific differences in evening emergence time among echolocating bats are subject to natural selection through effects of variation in food availability and predation risk, both of which are related to flight technique and foraging strategy. We predicted that bats that feed on small aerial insects emerge relatively early to get access to the peak in flight activity of small dipterans at dusk. By emerging well before dark, however, they expose themselves to increased risks of predation and/or harassment from raptorial or insectivorous birds which may still be active. Bats that can feed independently of the dusk peak of dipterans, i.e. those that are adapted to feed on moths, on flightless or diurnal prey or on plants, would be expected to emerge later, thus minimizing the predation risk. We tested these predictions by analysis of two data bases: one including European bats only and another including a worldwide sample. The predictions were largely supported. The evening emergence time appears to be a function of dietary specializations and foraging strategy, and is probably also affected by the ability to avoid predation.