THE INFLUENCE OF STRUCTURAL CLUTTER ON ACTIVITY PATTERNS OF INSECTIVOROUS BATS

We experimentally tested the hypothesis that three-dimensional structu ral clutter is a major factor affecting habitat choice by insectivorou s bats. To do this we artificially increased clutter at two sites used by bats without affecting prey availability. Our measure of available insect prey did not differ between treatment and control sites, indic ating that only the spatial complexity of the habitat type was manipul ated. Artificial clutter negatively affected foraging activity by smal l bats (Myotis spp.), supporting the hypothesis that physical clutter does affect foraging by bats. In direct contrast to our expectation, l arge bats (Eptesicus fuscus, Lasiurus cinereus, Lasionycteris noctivag ans) were apparently unaffected by the clutter treatment. We suggest t hat this may be an artifact of our experimental design, because our ul trasonic detectors probably recorded large bats flying above the artif icial clutter.