Studies of bats in southeastern Arizona with emphasis on aspects of life history of Antrozous pallidus and Eptesicus fuscus

Abstract

During 1980-1995, 42 cohorts of free-living juvenile female Antrozous pallidus and Eptesicus fuscus were banded and recaptured at three bridge roosts in Chihuahuan desertscrub in southeastern Arizona. Surviving female colony members returned each Spring to rear young. Life tables from known-age cohorts provided comparison of survivorship within and between populations sharing similar macro-environmental conditions at these maternity roosts. Mean first-year survivorship varied between and within species and roosts and was higher for E. fuscus than for A. pallidus. First-year survivorship was affected by weather, by age of mothers through indirect influence on neonate size with number of young in the litter, and by human activity. Disease, predation, inclement weather, and human vandalism caused mortality. Second and third-year survivorship was higher than juvenile year for both species. Eptesicus fuscus had higher adult survivorship than A. pallidus. Compared to A. pallidus, female E. fuscus had lower mortality rates, and females decreased their reproductive effort by litter size reduction and deferred age of first reproduction. While A. pallidus females began reproducing at yearling age, 54% of E. fuscus females deferred their first reproduction until age two. Fifty-five percent of age two A. pallidus and up to 100% of older females produced twins. By contrast, only 9% of age two E. fuscus had twins, and 28% of older females produced twins. Lower annual productivity by E. fuscus females was apparently balanced by longer life. While no more than 10% of A. pallidus reached five years of age, at least 10% of E. fuscus attained eight years. Thus, these species have evolved a life history that allows reproductive replacement with low fecundity and high survivorship. Western populations of E. f. pallidus produced smaller litters, deferred first reproduction, and had higher juvenile and adult survivorship than reported for E. f. fuscus, demonstrating intraspecific geographical differences in life history. Maximum life-span records for A. pallidus were a 10-year old male and a female that was at least 11 years old. The oldest E. fuscus were two females that were at least 14 and 15 years old.