Ecomorphology of Insectivorous Bats: A Test of Predictions Using Two Morphologically Similar Species

Abstract

Wing morphology and echolocation call design have been used to make predictions regarding habitat—use and resource partitioning in insectivorous bats. Species with very different morphologies and/or calls forage in different habitats or in different ways. However, bat communities contain many morphologically similar species, which would be predicted to overlap ecologically. We tested the reliability of such predictions and assumptions by investigating the habitat use and diet of two similar species, the little brown bat (Myotis lucifugus) and the long—legged bat (Myotis volans), in southern Alberta, Canada. We recorded the echolocation calls of free—flying individuals and measured wing morphology. The echolocation calls of the two species overlapped in design, although on average the calls of M. volans were shorter and had higher maximum frequency than those of M. lucifugus. Both species had low wing loading and aspect ratio although M. lucifugus had significantly higher values than did M. volans and was thus expected to forage in areas with less environmental clutter. Field observations did not substantiate this, however. We assessed the foraging ecology of the bats by: (1) monitoring species—specific echolocation calls of free—flying individuals, (2) capturing bats in mist—nets set in various habitats, (3) observing the foraging behavior of light—tagged individuals, and (4) assessing the diet from fecal samples. There was no evidence of temporal partitioning of resources by the two species, but some spatial partitioning occurred. Although individuals of both species generally fed in open areas, M. lucifugus foraged primarily low over water while M. volans fed high above the ground and along cliff edges. Neither fed consistently in cluttered areas despite wing and echolocation call designs that should permit such behavior. Despite the overlap in foraging areas, the diets of the two species differed significantly. Myotis volans ate primarily lepidopterans while M. lucifugus ate a wider variety of prey, including dipterans, lepidopterans, and coleopterans. Our results suggest that there are several levels at which morphology influences the ecology of insectivorous bats. Large differences may influence foraging—habitat choice by restricting some species to certain habitats. At another level, however, we suggest that small differences influence prey availability rather than habitat availability. Bats may select habitats based on the distribution of suitable prey rather than due to direct limitations imposed by morphology or echolocation call design.