Data from: Use of long-term opportunistic surveys to estimate trends in abundance of hibernating Townsend's big-eared bats

The advent of broad-scale threats to bats such as white-nose syndrome and
climate change highlights the need for reliable baseline assessment of
their populations. However few long-term, rigorously-designed assessments
of bats populations exist, particularly in western North America.
Consequently, results of informal monitoring efforts are often the only
data available upon which to base population assessments. We evaluated
whether an opportunistic collection of surveys recorded over a 22-year
period could be used to assess population trend of Townsend's
big-eared bats (Corynorhinus townsendii) at Lava Beds National Monument in
northern California. We used records of counts of hibernating bats
conducted during 1991-2012 to estimate the number of bats in 52 individual
caves as well as cumulatively. Seventeen of 22 caves surveyed in {greater
than or equal to} 4 years had an increasing trend in the number of
hibernating bats. We estimated the cumulative annual growth rate over the
period to be 1.79%. Stable or increasing number of hibernating
Townsend's big-eared bats may be a result of management actions taken
to limit disturbance of bats during maternity and hibernation seasons. We
found no evidence that annual counts depressed the number of hibernating
bats, thereby broadening monitoring options and the ability to link
population trends to extrinsic factors. Our results demonstrate that
opportunistically collected, long-term data sets may be useful for
establishing first approximations of population trends for bats.