Big brown bats (Eptesicus fuscus) frequently establish summer maternity colonies in houses and other human-built structures. These structures seem to be preferred by the bats over other potential roosting sites, and potentially provide the bats with physiological advantages related to the warm and relatively stable temperatures. While the timing of parturition and location of maternity colonies have been relatively well-studied, the actual process of parturition (giving birth) has not been systematically studied in bats in the wild. This study compares two similar maternity colonies, where the bats roost upon a 2-dimensional surface (mesh screen) that faciliates observation of the bats. The effects of microclimate on the parturition sequence (labor duration, position within the roost, percentage of twins). Within-roost behaviors, including the use of torpor and rates of aggression that occur during parturition, are also examined. To accomplish these goals, maternal colonies in Asheville NC and Richmond VA that occupy similar structures (attics of houses) are compared. Within each roost, temperature and illumination are continually monitored, and the bats are continually filmed under IR illumination.
Results/Conclusions
In North Carolina, the births occur within the first week of June. The majority of females (87%) produced twins, and parturition typically lasts 40-60 minutes in the 31 females that were observed. Within roost temperatures regularly exceed 40°C, and at these high temperatures, bats practice avoidance by moving to cooler parts of the roost. However, high temperatures are well tolerated, and appear to have no negative effect on the bats. While inter-individual aggression rates are high (occurring in 60% of females in active labor), rates of aggression do not seem to be related to duration of labor or within-roost temperature. Quantitative data from the colony in Virginia is still being analyzed at the time of abstract submission. The ability to handle and thrive in extreme temperatures characterizes big brown bats. The physiological robustness and willingness to use human-made structures may contribute to the survival of Eptesicus fuscus and the possible displacement of other less-hardy species as global temperatures increase.