A Retrospective Survival Analysis of Townsend's Big-Eared Bat (Corynorhinus townsendii) from Washington State

Abstract

Townsend's Big-eared Bat (Corynorhinus townsendii) is a species of conservation concern for many states and provinces. However, little is known about key demographic parameters, such as survival, for this species due to its sensitivity to human disturbance. This species can also be vulnerable to injuries from wing bands; the most commonly applied marking technique used in the past to estimate survival in bats. During the US Fish and Wildlife Service's Bat Banding Program (1932–1972), CM Senger banded 1,346 Townsend's Big-eared Bats at 3 major cave systems in Washington during 1964–1975, and continued to recapture banded bats until 1980. I applied current mark-recapture techniques to retrospectively estimate survival of hibernating Townsend's Big-Eared Bats banded by CM Senger. I also investigated sex, time, and trend effects on survival and capture probabilities of these 3 populations of bats using Cormack-Jolly-Seber (CJS) open models and the modeling capabilities of program MARK. For each location, estimates of annual survival and capture probabilities varied somewhat by sex and ranged from 0.54 to 0.68 for males and 0.60 to 0.67 for females. During the banding study, band injuries were noted and populations declined at all locations potentially violating assumptions of the CJS model. However, the dataset from which these estimates were derived is likely to be the most complete and well-maintained dataset in the Bat Banding Program files. Resulting annual survival estimates from these data were relatively precise and modeling provided evidence of time and trend effects and differences in survival between the sexes. These results provide historical, post hoc estimates of an important life-history parameter for this species of bat wintering in caves in 3 localized areas of Washington State.