Academic journal article The American Midland Naturalist

Seasonal Variation in Use of Caves by the Endangered Ozark Big-Eared Bat (Corynorhinus Townsendii Ingens) in Oklahoma

Academic journal article The American Midland Naturalist

Seasonal Variation in Use of Caves by the Endangered Ozark Big-Eared Bat (Corynorhinus Townsendii Ingens) in Oklahoma

Article excerpt

ABSTRACT.-We searched 19 caves, including known maternity roosts and hibernacula, in Adair and Delaware counties, Oklahoma, for the federally endangered Ozark big-eared bat (Corynorhinus townsend ingens) on eight occasions in 1989 and 1990. The same caves, and usually the same roost sites within caves, were used during summers as maternity roosts and during winters as hibernacula. An additional cave was used by large numbers of big-eared bats (>120 individuals) during spring and autumn of both years; this cave may serve as a transient roost and swarming site. At least one Ozark big-eared bat was found in 17 of 19 caves during one of the eight surveys; none was found in two caves during any survey. Numbers of bats using hibernacula varied markedly among November, December and February surveys, and we infer that Ozark big-eared bats were active during winter. Because big-eared bats move among hibernacula, accurate estimates of winter populations based on a single survey may not be possible.

INTRODUCTION

The Ozark big-eared bat ( Corynorhinus townsend ingens) was listed as an endangered subspecies in 1979 (U.S. Fish and Wildlife Service, 1984, 1995; see Tumlison and Douglas, 1992, for change from Plecotus to Corynorhinus); its current range is restricted to northeastern Oklahoma (Caire et aL, 1989) and northwestern Arkansas (Sealander and Heidt, 1990). Since Glass (1961) reported the first record of the Ozark big-eared bat in Oklahoma from a cave in Adair County, several studies have been conducted in Oklahoma on the life history of this subspecies (B. S. Clark, 1991; B. S. Clark et aL, 1993; Wethington, 1994; B. K Clark et aL, 1996). Data from these and other efforts recently culminated in a revision of the recovery plan for the Ozark big-eared bat (U.S. Fish and Wildlife Service, 1995). Ozark big-eared bats are obligate cave dwellers and occupy caves throughout the year (Humphrey and Martin, 1982; U.S. Fish and Wildlife Service, 1984, 1995). More than 100 potential roost sites, including limestone caves, talus slopes, and bluffs of exposed rocks, have been found in Adair, Cherokee and Delaware counties, Oklahoma, and Crawford and Washington counties, Arkansas. Although numbers of Ozark big-eared bats using known maternity caves and hibernacula have been monitored in summer and winter, respectively, for the last decade (see U.S. Fish and Wildlife Service, 1995), no systematic survey has assessed the temporal variation in numbers of Ozark big-eared bats using caves in eastern Oklahoma. The objective of this study was to examine seasonal variation in numbers of Ozark big-eared bats using caves in eastern Oklahoma, including known maternity caves and hibernacula. We also comment on the implications of fluctuations in numbers of bats on monitoring population trends as part of the recovery effort for this subspecies.

METHODS

The 19 caves selected for this study were located along the western edge of the Boston Mountains, a subsection of the Ozark Uplift, in Adair (18 caves) and Delaware (one cave) counties, Oklahoma (Huffman, 1959). Caves were systematically surveyed for bats in June, August, November and December 1989, and February, May, June and November 1990. All known maternity caves and hibernacula in Oklahoma were included. Caves were entered during daylight hours and numbers of Ozark big-eared bats were estimated. Small clusters of bats and solitary individuals were counted; numbers of bats in large clusters were estimated using a packing density of 16 bats/dm= (150 bats/ft2; proposed by Grigsby and Puckette, 1982). To minimize disturbance to bats, we used infrared filters on flashlights, observed bats on ceilings just long enough to count numbers or estimate size of clusters, traveled near cave walls or floors and exited caves immediately after collecting pertinent data. A video camera and night vision scope also were used to record numbers of adult females emerging from maternity caves after sunset in June 1989 and June 1990 (B. …

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