Summer activity patterns of four resident south Texas bat species

Abstract

Although the activity patterns of bats are recognized to vary widely, both, temporally and spatially, the underlying drivers for those patterns remain poorly understood. Presently, studies focusing on foraging bat ecology have only generalized activity and influence of the environment (across sampling periods, sampling nights, or seasons). The influence of environmental features on foraging bat activity on a finer temporal scale (e.g., throughout a single sampling night) is markedly less studied. The recent emergence of Pseudogymnoascus destructans, a cold-adapted fungus and the causative agent of white-nose syndrome (WNS), has led to the precipitous declines in North American bat populations since its arrival in 2006. P. destructans has been recently documented in 10 Texas counties and, although WNS primarily affects hibernation cycles, it is recognized to have significant detrimental impacts on summer bat activity. It is imperative we understand and provide a baseline of summer bat activity patterns prior to the arrival of WNS to better manage and protect these, relatively understudied, populations of bat species in south Texas. We used a mixed model approach and acoustic monitoring to quantify how shrub density, canopy height, distance to water, roads, and bare ground coverage influenced nightly foraging activities of four summer resident bat species in south Texas: Eastern Red Bat (Lasirius borealis), Cave Myotis (Myotis velifer), Evening Bat (Nycticeius humeralis), and Brazilian Free-tailed Bat (Tadarida brasiliensis). Total bat activity peaked at 2:00-a for all species included in our study. A secondary, smaller peak was notable between 5:00-a and 6:00-a and activity decreased sharply immediately following 6:00-a. However, the trend for total bat activity differed substantially from trends exhibited by the individual species. Eastern red-bats and Evening bats exhibited bimodal nightly activity patterns and showed variable associations with water proximity whereas Cave bats and Brazilian free-tailed bats exhibited unimodal activity patterns and strong associations with canopy height and roads. Our results support the concept that insectivorous bats partition resources, temporally and spatially, in the presence of other sympatric species.