Conservation Status of the Endangered Ozark Big-eared Bat (Corynorhinus townsendii ingens) - a 34-year Assessment

Abstract

Direct counts of Ozark big-eared bat (Corynorhinus townsendii ingens) in hibernacula and maternity roosts were analyzed from 1977 to 2010. We compiled data from 1,330 survey events at 268 sites: 77 sites known to be used in Arkansas, 84 in Oklahoma, 9 in Missouri, and 98 potential use sites. Survey techniques were standardized, and baseline population indices established. Rank correlation techniques of population indices (Mann-Kendall Test) at 19 essential sites revealed important demographic trends over this 34-year period: 7 colonies have a significantly increasing trend—3 maternity sites (Cave No. AD10, AD17/18, and CW29BT3) and 4 hibernacula (AD14/125, AD3, ADT1, and WA31T complex); 3 colonies are decreasing—the maternity sites AD125 and AD13/24/25, and hibernaculum MR0702/9702/979a; and the remaining essential sites are data deficient. Historic total abundance estimates of Ozark big-eared bats ranged widely from less than 100 in 1973 to 2,500 individuals in 1990; the current population estimate is 1,600 to 1,800 bats. When all site counts are pooled by year, trend analyses indicate an increase in all maternity and hibernaculum counts over the last 34 years. Confounding this apparent increase is the discovery of new maternity colonies and hibernacula. Human disturbance and habitat loss appear to be the most important limiting factors, as the behavior and life history of this species make it inherently vulnerable to anthropogenic disturbances. Colony protection (primarily via cave gating), habitat protection (via conservation easement and fee title acquisition), and landowner management agreements have been particularly effective, yet additional time is needed before this bat’s conservation status can be upgraded.