Methods for Assessing the Distribution, Activity Rates, and Health of Bat Populations

Rojas, Vanessa

ABSTRACT: For effective conservation, it is necessary to study the presence and distribution of bats, which are long-lived, high trophic level consumers largely dependent on forested environments. Bats are sensitive to habitat loss, particularly forest fragmentation, and bats are also excellent bioindicators of environmental degradation, such as contamination by heavy metals. In North America, bat populations are experiencing significant declines due to white-nose syndrome, habitat loss, and other anthropogenic impacts; thus, it is becoming increasingly difficult to study bat presence and species’ distributions. In this dissertation, I compare survey methods and analytical techniques for assessing detection and occupancy rates for rare bats, present data and discuss important considerations for analyzing data collected along mobile acoustic survey routes, and describe heavy metal loads for common bat species in urban and rural areas. In Chapter 1, we assessed the performance of false-positive versus standard occupancy models and important factors predicting presence for a low-density bat population, northern long-eared bats (Myotis septentrionalis). We surveyed 35 sites in the northern districts of the Cherokee National Forest in northeastern Tennessee using both mist-net and acoustic methods. False-positive models received more support, while none of the standard occupancy models were plausible. In addition, false-positive occupancy models produced a wider range of probability of occupancy estimates (0.004–0.998) and a lower mean occupancy estimate (0.62) than standard models (0.482–0.970, mean = 0.859). Important predictors in two plausible false-positive occupancy models indicated that the probability of occupancy for northern long-eared bats was higher at less rugged, lower elevation sites. Due to low capture rates and the uncertainty of acoustic identifications with northern long-eared bats, we recommend coupling a certain method with uncertain methods. Applying false-positive occupancy models to our data yielded less biased site-specific occupancy estimates and informative predictors, and, hence, more reliable predictions to inform conservation management plans. In Chapter 2, we conducted mobile survey methods along 12 transect routes in order to survey bat populations across a large area and assess the relative effects of land cover types on the distribution of three phonic groups (Low, Mid, Myotis). Mobile transect guidelines recommend conducting surveys on straight routes to reduce the chance of duplicate recordings of an individual bat. We tested the effects of road sinuosity on the number of call files recorded during a transect survey in a mountainous region of Tennessee. We found that in this study region, sinuosity did not affect the number of identified acoustic files. Next, we assessed bat occupancy for each phonic group. As the proportion of agriculture within a 250-m buffer around the transect segment increased, the probability of occupancy for low-frequency bats decreased. The proportion of forest within a 250-m buffer surrounding the transect segment had a positive effect on occupancy of Myotis bats. None of the parameters we tested (proportion of forest and proportion of agriculture in the 250-m buffer surrounding the segment, distance to lakes/rivers, distance to city, and elevation) were informative regarding mid-frequency bat occupancy. We recommend following the guidelines set forth by the North American Bat program for mobile acoustic surveys, but note that sinuosity of the route did not affect the number of calls recorded in our study; thus, we suggest that curvy roads in mountainous terrain not be excluded from mobile acoustic transects. Finally, in Chapter 3 we focused on the health of bat populations in the southern Appalachian and central Indiana regions. Bats are high trophic level consumers that live relatively long lives, and thus, are excellent bioindicators. We compared heavy metal concentration levels in bat populations in the southern Appalachian region and for bat populations at sites closer to urban areas in Indiana. From May to July 2009–2017, we collected fur from big brown bats (Eptesicus fuscus) and eastern red bats (Lasiurus borealis) captured in the Cherokee and Nantahala national forests and the Great Smoky Mountains National Park (Southern Appalachian sites), and Yellowwood and Morgan-Monroe state forests, and Indianapolis Airport Authority property (Indiana sites). In the lab, we analyzed metal concentrations (Ba, Cd, Cr, Cu, Fe, Pb, Zn) within samples using an Inductively Coupled Plasma–Optical Emission Spectrometer. We compared heavy metal concentrations between regions, sex, and species. We saw differences in heavy metal concentration levels between study areas and among species-sex groups. We used mist net surveys, plus stationary and mobile acoustic methods to survey bat populations in northeast Tennessee, where fragmentation and environmental contamination issues exist. Estimating probability of occupancy, determining the effects of land use on bat distribution, and identifying levels of heavy metal contamination in bats in relation to their habitats can aid land managers with conserving imperiled bat populations in areas subject to anthropogenic pressures such as forest fragmentation and environmental degradation.