Masters Theses

Ya-Fu Lee

Date of Award

12-1993

Degree Type

Thesis

Degree Name

Master of Science

Major

Ecology and Evolutionary Biology

Major Professor

Gary F. McCracken

Committee Members

David A. Etnier, Virgil Brack Jr., Karen Tyrell, John Gittleman

Abstract

Feeding strategies and food habits of insectivorous bats in the temperate zone may show intraspecific or interspecific variation due to internal factors (e.g. different energy demands, morphological differences) or external factors (e.g. the distribution and abundance of insect prey, interactions with other sympatric bat species). The present study (1) describes the resource utilization of Myotis sodalis in their summer nursery habitats and (2) investigates whether prey selection differs among bats with regard to their age, sex, and the different reproductive status of females. This study also (3) tests the hypothesis that insectivorous bats tend to be opportunistic in foraging, and (4) investigates whether M. sodalis, M. keenii (septentrionalis)M. lucifugus partition available food resources by foraging in different locations, at different times, or by selecting different prey.

Bats were mist-netted at 94 sites in central and northern Indiana during the summers of 1991 and 1992. Insect availability was assessed at the same sites using sticky traps and light traps. The activity times and height distributions of foraging bats were determined by the times and heights at which bats were netted. Myotis sodalis and M. keenii showed temporal separation at sites where both species were caught. Myotis sodalis and M. lucifugus foraged at different heights when both species were netted together on the same nights at the same sites.

Fecal pellets were collected from captured bats for dietary analysis. The body sizes of the prey taken were estimated by measuring the femora lengths of Coleoptera found in fecal samples. Intraspecific dietary variation in M. sodalis and interspecific dietary variation among the three Myotis species were investigated at sites where different groups (sex, age, reproductive status) of M. sodalis were netted or where the three species were netted. The correspondence of diets to prey availability, and diet preferences of the three Myotis species for major prey taxa were assessed relative to the different availability of prey taxa.

Lepidoptera was the major prey of M. sodalis throughout both field seasons; however, dietary variation occurred among the different age, sex, and reproductive status groups. Adult females consumed more aquatic insects than adult males and juveniles. Lactating females had the highest dietary diversity. Juveniles and pregnant females also had higher dietary diversities than nonreproductive adult females and adult males. Presumably, the higher energy demands of reproductive females and juveniles resulted in a more general diet. The lower consumption of Lepidoptera and Trichoptera by juveniles may have been due to their less efficient echolocation and flying capability.

Myotis keenii fed primarily on Coleoptera, Lepidoptera, and Diptera, and took more large Coleoptera (over 6 mm) than M. sodalis and M. lucifugus. Myotis lucifugus had the highest dietary diverstiy, fed on more small prey (0-4 mm), and consumed more aquatic insects than the other two Myotis species. Both M. sodalis and M. keenii had higher preference for Lepidoptera and Coleoptera than M. lucifugus. The interspecific dietary variation among these three species is compatible with their foraging activity patterns and with morphological differences in their jaw lengths. Myotis sodalis had a relatively narrower diet. However, all three species showed evidence of opportunistic feeding by apparently switching prey selection due to changing prey abundance or due to interactions with associated species. These results and the temporal and height distributions of bat captures suggest evidence for resource partitioning between these three Myotis species within areas of sympatry.

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