Long-term bat abundance in sagebrush steppe

Justin A Frye,Brent J Sewall,Devin K Englestead,Gary Wright,Jericho C Whiting,Todd Stefanic,Bill Doering

doi:10.1038/s41598-018-30402-z

Abstract

Bats of western North America face many threats, but little is known about current population changes in these mammals. We compiled 283 surveys from 49 hibernacula over 32 years to investigate population changes of Townsend’s big-eared bats (Corynorhinus townsendii townsendii) and western small-footed myotis (Myotis ciliolabrum) in Idaho, USA. This area comprises some of the best bat habitat in the western USA, but is threatened by land-use change. Bats in this area also face invasion by the pathogen causing white-nose syndrome. Little is known about long-term trends of abundance of these two species. In our study, estimated population changes for Townsend’s big-eared bats varied by management area, with relative abundance increasing by 186% and 326% in two management areas, but decreasing 55% in another. For western small-footed myotis, analysis of estimated population trend was complicated by an increase in detection of 141% over winter. After accounting for differences in detection, this species declined region-wide by 63% to winter of 1998–1999. The population fully recovered by 2013–2014, likely because 12 of 23 of its hibernacula were closed to public access from 1994 to 1998. Our data clarify long-term population patterns of two bat species of conservation concern, and provide important baseline understanding of western small-footed myotis prior to the arrival of white-nose syndrome in this area.

Highlights

Bats of western North America face many threats
We compiled a long-term, regional-scale dataset from bat monitoring, and used generalized additive mixed models (GAMMs)[35,36,37] to understand population trajectories of Townsend’s big-eared bats and western small-footed myotis—both species of conservation concern18,38—while addressing factors that have previously complicated analyses of wildlife monitoring data[19,39]
We focused on repeatedly surveyed caves that served as hibernacula for ≥ 1

Summary

Introduction

Bats of western North America face many threats. Disturbance during hibernation and destruction of hibernacula by humans have long been concerns for bat conservation in many areas[1,2,3]. The recent arrival of white-nose syndrome, a deadly disease of hibernating bats[7,8] in western North America[9], is an important emerging threat to bats in this region This disease has led to mass mortality in seven bat species in eastern and midwestern North America[10,11], resulting in severe regional declines in several species[10,12], and the potential for regional extirpation of some species within the decade[13,14]. These threats make an understanding of population changes in western bats essential for the conservation of these mammals and their habitat[15,16]. Our results will clarify long-term trajectories of these populations, suggest possible causes for population changes, and provide baseline data in a region at risk for imminent invasion by white-nose syndrome

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