Video exit counts of gray bats (Myotis grisescens).

Conservationists are actively working to stem the decline of gray bats (Myotis grisescens) in the eastern United Sates. The estimation of colony size can be used to evaluate the success of gray bat conservation efforts and properly guide future management decisions. Although many survey techniques can be used to estimate colony size, exit counts are the least intrusive, can be the most accurate and can be reported with significance values. The current study at Tumbling Creek Cave, Taney County, and other Missouri caves employs the use of simple video recording equipment, infrared lighting and slow motion playback. Using this method, in addition to a cluster sample counting technique, we conducted exit count surveys at a reasonable cost, and we obtained statistical confidence values. We found that there was a general trend of increasing gray bat colony size throughout the summer season, and we observed variation between successive nights. In addition, during internal, night surveys in the cave, we witnessed monthly changes in the location of the maternity roost. Such switches generally occur between geographically close caves and are rarely within cave movements. We placed plastic plates beneath all known roost sites to collect guano. We observed the amount of guano deposited on each plate monthly to determine the most recently used roost. The maternity colony was observed roosting at five different sites separated by a considerable distance; young bats were found in three of these locations through the months of May to July.

* Samoray, S.T., S.E. Gardner and W.R. Elliott. Resource Science Division, Missouri Department of Conservation, Jefferson City.