Notes on the late summer diet of male and female eastern pipistrelles (Pipistrellus subflavus) at Fort Mountain State Park, Georgia

Georgia Journal of Science, 2002 by Menzel, Michael A Jr, Menzel, Jennifer M, Carter, Timothy C, Whitaker, John O Jr, Ford, W Mark

ABSTRACT

On 21 August 1998, we collected fecal samples from 37 eastern pipistrelles (6 females and 31 males) from an abandoned talc mine at Fort Mountain State Park in Murray Co., Georgia and examined them to determine diet. We also compared the diet between females and males. We detected insect fragments from six insect orders in the fecal samples: Homoptera, Coleoptera, Diptera, Lepidoptera, Hemiptera and Hymenoptera. Female eastern pipistrelles foraged primarily on Homoptera (47.0 /- 14.07%) and Coleoptera (17.5 /- 12.63%), whereas males foraged primarily on Diptera (32.3 /- 17.71%) and Homoptera (18.2 /-- 4.81%). Sex-based differences were dramatic at the family level and insect size categories. Cicadellidae comprised 46.7% ( /- 14.24%) of female eastern pipistrelles' diet but only 18.2% ( /- 4.81%) of the males' diet. Unidentified small Dipterans comprised 21.3% ( /- 6.74%) of male eastern pipistrelles' diet, whereas none of these was detected in female fecal samples. Our study provides information that suggests late summer diets of eastern pipistrelles in northwest Georgia are contrary to previous diet studies of other pipistrelle species. Moreover, the diets of female and male eastern pipistrelles may differ during certain seasons or in particular regions of the species' range.

Key Words: diet, eastern pipistrelle, Fort Mountain State Park, Pipistrellus subflavus

INTRODUCTION

Few studies have investigated the diet of most bat species (1). However, diet data are available for pipistrelles in general (e.g. Pipistrellus pipistrellus; 2), and the eastern pipistrelle in particular (1, 3-8).

One of the first eastern pipistrelle diet studies was by Hamilton in 1930 in Kentucky (3). He noted that the diet consisted of Diptera and Coleoptera (Table 1). A few years later, Sherman (4) found fragments of Diptera (specifically the family Anthomyiidae) and Hymenoptera (specifically Formicinae, ants) in an eastern pipistrelle stomach he examined from Florida. Approximately 10 years later, Barbour and Davis (5) reported observing eastern pipistrelles foraging on Lepidoptera that were emerging from a corn crib in eastern Kentucky.

In 1972, Whitaker (1) conducted the only study of eastern pipistrelles' diet that involved examining samples collected from a relatively large number of individuals. From the contents of 23 eastern pipistrelle stomachs, Whitaker found that the diet was mostly Homoptera (specifically cicadellids) and Coleoptera (specifically carabids), followed by small amounts of Diptera and Lepidoptera.

Isolated research on the diet of a total of

A review of eastern pipistrelle food habits suggests the diet can vary greatly (Table I). Although some of this diet variability probably is the result of temporal or spatial differences in foraging, it may indicate that eastern pipistrelles may be able to take advantage of a wide variety of foods when available. Swift et al. has reported that Pipistrellus forage opportunistically, preying on each insect order in roughly the same proportion as available in the environment (2). However, Carter et al. (7) suggested that eastern pipistrelles did not forage opportunistically and found that 66% of the "forageable-sized" insects in the environment consisted of Coleoptera, but only 6% of the eastern pipistrelle diet consisted of insects from this order. Conversely, only 5% of the insects in the environment were Lepidopterans, whereas 74% of the fecal samples examined contained Lepidoptera.

The objectives of this study were (1) to determine the insect orders that occurred in eastern pipistrelle diets in the extreme Southern Appalachians of northwestern Georgia, and (2) to document and compare our results with previous studies of eastern pipistrelle food habits.

MATERIALS AND METHODS

We conducted our survey at Fort Mountain State Park in Murray Co., Georgia. Fort Mountain State Park is located in the Blue Ridge physiographic subsection of the Southern Appalachians in northwestern Georgia. On 21 August 1998, we placed two harp traps (1 X 1.5 m; 9, 10) over the entrance to an abandoned talc mine at 595 rn elevation on the northwest-facing slope of Cohutta Mountain. We also set three mist nets in front of canopy gaps at the mine entrance. We opened harp traps and mist nets at dusk (ca. 2100 hrs.) and closed them at 0200 hrs.

After removing bats from the harp traps and mist nets, we determined sex, species, reproductive condition, and mass. Studies have shown that fecal analysis is a useful method for determining the food habits of bats (11). After each bat was examined and measured, it was placed in a 946-cm^sup 3^ plastic cup for 20 mins. Bats were released after 20 mins., regardless of whether a fecal sample had been collected. Of 125 eastern pipistrelles captured, 37 (30%) provided fecal samples.

For food-habits analysis, fecal samples were placed in a petri dish, softened with ethanol, and teased apart with probes and forceps (12). We examined all samples collected from a single individual together using a dissecting microscope. Because of the subjective nature of fecal analysis, one author (JOW) analyzed all fecal samples. We visually estimated percent volume of each insect order in each fecal sample. Because Lepidopterans often were represented only by scales in the fecal samples, we estimated their percent volume in the fecal samples (13).