Effects of moonlight on the capturability of frugivorous phyllostomid bats (Chiroptera: Phyllostomidae) at different time scales

Marco A R Mello,Wesley R Silva,Elisabeth K V Kalko

doi:10.1590/s1984-46702013000400005

Abstract

Some bat species seem to be lunar phobic, i.e., they avoid flying in bright areas or during bright periods of the night; however, the evidence is still controversial. We think that part of this controversy comes from pooling data on bat captures and moonlight intensity according to broad categories, such as moon phases, which conceal the high variability among nights. Therefore, we used detailed, long-term field data on three phyllostomid bat species, in order to test the hypothesis of lunar phobia at two different time scales: 1) among nights, by pooling data of different nights according to moon phases and testing for differences in the distribution of captures; and 2) within a night, by analyzing the relationship between capturability and moonlight intensity (measured as illuminance) in one-hour intervals for 29 individual nights. Although most captures of the studied bat species occurred in the first half of the night, their activity pattern varied largely among nights, and was not always unimodal as commonly assumed. At the larger time scale, all studied bat species showed evidence of lunar phobia, as they were more frequently captured on dark moon phases. Nevertheless, at the smaller time scale, only Carollia perspicillata (Linnaeus, 1758) was less frequently captured on brighter periods of the night. We propose that the unimodal activity pattern assumed for frugivorous phyllostomid bats may be an artifact of data organization, and that activity and lunar phobia are much more variable than previously assumed.

Highlights

As proposed first by MÁLAGA (1954) and observed in subsequent studies (e.g., CRESPO et al 1972, ESBERARD 2007), some bat species tend to be less active on brighter nights. MORRISON (1978) coined the term ‘lunar phobia’ to explain this behavior: some nocturnal animals avoid brighter periods of the night, in order to reduce predation risk, as their main natural enemies are visually oriented
We propose that the unimodal activity pattern assumed for frugivorous phyllostomid bats may be an artifact of data organization, and that activity and lunar phobia are much more variable than previously assumed
In the present study, using detailed, long-term field data, we observed that the capturability of three very common species of frugivorous phyllostomid bats is highly variable among nights, and that evidence of lunar phobia are observed at a large time scale, but not at a smaller scale

Summary

Introduction

As proposed first by MÁLAGA (1954) and observed in subsequent studies (e.g., CRESPO et al 1972, ESBERARD 2007), some bat species tend to be less active on brighter nights. MORRISON (1978) coined the term ‘lunar phobia’ to explain this behavior: some nocturnal animals avoid brighter periods of the night, in order to reduce predation risk, as their main natural enemies are visually oriented. For bats (Mammalia: Chiroptera), positive (ELANGOVAN & MARIMUTHU 2001) and negative (GANNON & WILLIG 1997) evidence of lunar phobia has been obtained. This controversy may result from ecological differences among bat species. There seem to be differences among data collection methods, as evidence from radio-tracking and mist netting studies, for instance, are sometimes contradictory (THIES et al 2006). If phyllostomid bats really avoid brighter nights or periods of the same night, in order to escape predators, we expected a lunar phobic bat species to show this behavior at both time scales

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