Survivorship in the Endangered Gray Bat (Myotis grisescens)

Abstract

Analyses of gray bat survival were made for three summer colonies, based on band recoveries in two hibernacula. Recoveries made in each hibernaculum were compared by sex and age groups both within and between summer colonies. No comparisons were made between hibernacula, even for individuals from the same summer colony, due to differential hibernaculum band recovery success. One summer colony was represented well in both hibernacula, providing a measure of the extent of this bias. The data were analyzed with regression and nonparametric trend test techniques, and the two methods were compared. Census estimates from 1970 and 1976 provided additional information on survivorship in the colonies. Results of the trend tests represent the relative survivorship of the colonies more accurately than the regression analyses. Differential recapture success in different hibernacula was shown to affect strongly life table results. The census and recovery results document the severe decline of a major colony in Alabama and suggest a major decline in a majority of other colonies that use the hibernaculum in Alabama. Survival rates in the declining colony ranged from 6.0 to 13.9% in the first year after banding and 57.0 to 65.5% in subsequent years. Rates in the stable colonies were 17.2 to 72.7% and 65.7 to 85.1%, respectively. No significant differences were found in survival between sex and age groups within colonies, but significant differences did exist between colonies. Gray bats clustered nonrandomly with respect to both sex and age. Highly significant differences in these variables were found within clusters of bats according to edge versus center, height above floor, and location within or among rooms. Bats roosting singly differed significantly in age from those roosting in clusters. Banded gray bats showed a significant tendency to avoid, when possible, roosts where they had been handled by researchers.