A Study of Hibernating Populations of Myotis Velifer In Northwestern Texas

A 5-year study of hibernating colonies of Myotis velifer in northwestern Texas was conducted by recapture of banded bats and by experimentation. Nearly 17,000 captures of 12,000 bats provided most information. The bats occur in small hibernating colonies of 1,000–5,000 and rarely make major movements during the winter. Movements within a cave and to adjacent caves are frequent, perhaps for the purpose of selecting sites where the temperature is suitable for maintaining a metabolic rate optimal for maximum energy conservation. Short movements of less than 100 miles occur in the spring from hibernacula to nurseries in warmer caves. Temperature, relative humidity and air movement all seem important in effecting stability of clusters of hibernating bats. Weight loss occurs throughout hibernation, but especially in the early months. Most temperatures of hibernating bats range from 1–10° C, which is similar to the range in ambient temperatures. Sex ratios are unbalanced in favor of females and several factors responsible for this imbalance are discussed. About 25% of banded bats were not recovered in the season immediately after banding or were recovered in nonconsecutive hibernating seasons. This fact introduces some error into estimated population loss. The mean duration of the presence of a bat in the hibernating populations is about 2 years; bats older than 5 years apparently make up a small fraction of the breeding population. Ninety-five per cent of the banded bats accounted for returned to the same area for hibernation. Quantitative data are provided for the population parameters discussed, and comparative data for other species are presented.