Erin H. Gillam

Brazilian free-tailed bats (Tadarida brasiliensis: Molossidae, Chiroptera) at high altitude: links to migratory insect populations

Existing information on the activity of bats in the aerosphere is restricted almost exclusively to altitudes that are within a few tens of meters above the ground. We report a total of 50.2 h of ultrasonic recordings made using radio microphonic bat detectors suspended from free-floating helium balloons and from kites. The data include a total of 22 353 echolocative calls from ground-level to 1118 m above ground level (AGL). These calls are attributed to Brazilian free-tailed bats based on acoustic features and the large numbers and high-altitude aerial dispersion of these bats over the local landscape. Bat activity varied significantly throughout the air column and was greatest at 400-500 m AGL and near ground level. Feeding buzzes, indicating feeding on aerial prey, were most abundant near ground level and at 400-500 m, and were detected to altitudes of ∼ 900 m AGL. The peak activity of bats at 400-500 m AGL is concordant with the altitude of the atmospheric boundary layer and the seasonal formation of the low-elevation southerly wind jet that has been identified as a major aeroecological corridor for the nocturnal dispersal of noctuid moths and other insects.

Echolocation behavior of Brazilian free-tailed bats during dense emergence flights

Abstract Brazilian free-tailed bats (Tadarida brasiliensis) emerge from cave roosts in dense columns in which adjacent bats are separated by only small distances. We describe and quantify variation in the structure of echolocation calls produced by these emerging bats and determine if call structure changes in relation to the rate of emergence measured using thermal infrared imaging. We recorded emergence calls at 2 roosts, 1 housing approximately 200,000 bats and the other approximately 17,000 bats. We found that Brazilian free-tailed bats emit distinct frequency-modulated (FMstart) and constant frequency (CFstart) calls during emergence that are significantly different from echolocation calls they emit while foraging. We propose that these calls provide different information for orientation within the emergence column. CFstart calls are very similar to social calls used by Brazilian free-tailed bats, suggesting 2 potential functions for this call type. The structure of both the FMstart and CFstart calls were not related to the number of bats emerging from a roost, although significant structural differences existed between sites. The differences between sites could be associated with the spacing of bats during emergence, because bats appeared to form tighter columns at the larger roost colony compared to the smaller colony.

The Impact of Sampling Method on Maximum Entropy Species Distribution Modeling for Bats

As species distribution modeling (SDM) becomes more commonly incorporated into ecological studies, there is a need to address how the use of different sampling techniques for assessing the presence of a species can impact the final models produced. Over a four-year period, we sampled for the presence of bats throughout North Dakota via mist netting (physical capture) and ultrasonic acoustic monitoring. We used maximum-entropy modeling to develop habitat suitability maps for each study species using physical capture data, acoustic data and both detection techniques combined. We evaluated the amount of niche overlap between maps to determine how sampling technique impacted the final SDMs and which technique was best for modeling SDMs for each species. We found variation among species in the amount of overlap between SDMs, ranging from pronounced differences (33.9% overlap; Myotis septentrionalis) to highly similar models (80.4% overlap; Myotis lucifugus). Our findings show that acoustic detection results in better SDMs for Myotis spp. while physical capture was best for modeling Eptesicus fuscus and Lasionycteris noctivagans. Although both methods produce highly reliable SDMs, care must be taken when using maximum-entropy modeling for species in which presence data can be gathered in multiple ways. We emphasize that researchers should consider the ecology and behavioral characteristics of their focal species to address any biases associated with sampling technique.

Documentation of Overwintering Bat Species Presence and Hibernacula Use In the Badlands of North Dakota

Abstract Little work has focused on species presence, distributions, and habitat use of bats in the Great Plains of North America. In particular, no previous study has attempted to determine if bats are utilizing hibernacula during the winter months in North Dakota. The current lack of information regarding bat species presence during the winter months in North Dakota can have great conservation implications. Pseudogymnoascus destructans, the fungal pathogen responsible for white-nose syndrome (WNS) in bats across the United States and Canada, has led to great concern for wildlife managers. For many of the areas where WNS is present, information about the presence and location of hibernacula are known, allowing for close monitoring of the spread of the disease. However, some locations within the predicted path of WNS still lack information as to bat species presence during the winter months. Due to mortality rates sometimes reaching upwards of 100% as a result of WNS infection, filling in these information gaps is critical for conservation research. The purpose of this study was to determine if the badlands region of North Dakota supports over-wintering bat communities, document both utilized and potential hibernacula, and develop a Geographic Information Systems model in the program MaxEnt to be used for future studies and wildlife managers. Six species were positively identified in the badlands region of North Dakota during the pre-hibernation and winter hibernation periods: Big Brown Bat (Eptesicus fuscus), Silver-haired Bat (Lasionycteris noctivagans), Little Brown Bat (Myotis lucifugus), Long-eared Myotis (Myotis evotis), Townsends Big-eared Bat (Corynorhinus townsendii), and Western Small-footed Myotis (Myotis ciliolabrum). Habitat suitability modeling was employed to model potential hibernacula in the study area. Knowledge of these potential hibernacula could be of great importance to wildlife managers, and results from this study may be used by regional wildlife managers to develop strategies for curtailing the spread of this disease into North Dakota.

Understanding Peripheral Bat Populations Using Maximum-Entropy Suitability Modeling

Individuals along the periphery of a species distribution regularly encounter more challenging environmental and climatic conditions than conspecifics near the center of the distribution. Due to these potential constraints, individuals in peripheral margins are expected to change their habitat and behavioral characteristics. Managers typically rely on species distribution maps when developing adequate management practices. However, these range maps are often too simplistic and do not provide adequate information as to what fine-scale biotic and abiotic factors are driving a species occurrence. In the last decade, habitat suitability modelling has become widely used as a substitute for simplistic distribution mapping which allows regional managers the ability to fine-tune management resources. The objectives of this study were to use maximum-entropy modeling to produce habitat suitability models for seven species that have a peripheral margin intersecting the state of North Dakota, according to current IUCN distributions, and determine the vegetative and climatic characteristics driving these models. Mistnetting resulted in the documentation of five species outside the IUCN distribution in North Dakota, indicating that current range maps for North Dakota, and potentially the northern Great Plains, are in need of update. Maximum-entropy modeling showed that temperature and not precipitation were the variables most important for model production. This fine-scale result highlights the importance of habitat suitability modelling as this information cannot be extracted from distribution maps. Our results provide baseline information needed for future research about how and why individuals residing in the peripheral margins of a species’ distribution may show marked differences in habitat use as a result of urban expansion, habitat loss, and climate change compared to more centralized populations.

Development of the Over-Water Mist Net Support System: A Novel Ecological Research Tool

The habitats in areas like the Northern Great Plains of North America present challenges to bat researchers in the field. Due to limited vegetative cover, mist-netting efforts often must be concentrated over ponds, streams or rivers. This can present problems to researchers, such as deep water, soft mud bottoms or uneven terrain, all of which can make traditional mist netting difficult and unproductive. While boats can be useful under these circumstances, this leads to additional safety and logistical challenges. The purpose of this study was to address these problems by developing a novel tool that permits sampling with mist nets over water without the need to directly enter the water. We developed a basic conceptual design for a mechanical gate-like support system that: 1) supports a traditional mist net system, and 2) swings out over a body of water. Initial results indicate that the over-water mist net support system is an effective, versatile research tool that allows researchers to sample for bats under challenging field conditions in which placement of traditional mist net systems would be dangerous or not feasible.