Are Bats in Indiana Declining

Abstract

The number of big brown bats in Indiana was estimated using an estimated number of colonies per county times the average number of bats per colony times the number of counties in the state. Estimates of the number of individuals of other species in the state were assessed using their relative abundance by mist-netting in relation to the big brown bat. Assessment of population levels over time was made by examining four decades of submission of specimens to the Indiana Department of Health rabies lab. Twelve species of bats are known from Indiana, of which one, Rafinesque's big-eared bat, Corynorhinus rafinesquii, occurs only sporadically and is considered of accidental occurrence. Myotis austroriparius was known to hibernate in certain caves in south central Indiana through the early 1970's, but it is apparently now extirpated. This leaves ten species of bats in the state. Two - the gray myotis, Myotis grisescens, and the Indiana myotis, Myotis sodalis - are on the federally-endangered list. However, there is only one colony of gray myotis in the state. It is in Clark County and has increased from about 400 bats in 1982 to about 4000 today. The Indiana myotis has increased from about 124,000 in 1980 to about 173,000 today, whereas rangewide, that species has declined from about 589,000 in 1980 to 381,000 today. Four other species appear to have declined in Indiana since 1980: the evening bat, red bat, hoary bat and little brown myotis. The big brown bat, eastern pipistrelle, and silver-haired bat may have in- creased. The northern myotis apparently has remained relatively stable over this period.