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Use of Long-Term Opportunistic Surveys to Estimate Trends in Abundance of Hibernating Townsend's Big-Eared Bats




Publication type:

Scientific Journal (JRNL)

Primary Station(s):

Pacific Southwest Research Station


Journal of Fish and Wildlife Management. 5(1): 59-69


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 bat 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-y 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 four or more 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.


Weller, Theodore J.; Thomas, Shawn C.; Baldwin, James A. 2014. Use of Long-Term Opportunistic Surveys to Estimate Trends in Abundance of Hibernating Townsend's Big-Eared Bats. Journal of Fish and Wildlife Management. 5(1): 59-69.


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