Anti-Predator Behavior and Winter Activity in Midwestern Bat

The main goal of my dissertation work was to describe and understand the main factors influencing the activity of bats during both summer and winter. There are several factors that could influence the activity of bats, such as the presence of predators and food resources. During the summer activity season, predator-sensitive activity appears to be common among tropical bat species, and is often associated with important tradeoffs between resource acquisition and predation risk. However, whether the activity of temperate-zone bats is similarly predator-sensitive is unclear. Bat activity during the winter months is not well characterized, but could be a pervasive aspect of the biology of wintering bats. My dissertation work provides the first in-depth investigations into these two aspects of bat activity.;Chapter 2 addresses the timing of emergence from roosts in a colony of endangered Indiana bats (Myotis sodalis), using a long-term dataset from central Indiana. Emergence from roosts generally began shortly after sunset, but sometimes occurred before or well after sunset. Using an information- theoretic approach, I compared statistical models representing hypotheses based on three broad environmental influences: predators, competition, and physical variables (meteorological and astronomical). The best performing models included most of the variables associated with anti-predator trade-offs, assuming that early-emerging bats experience a foraging benefit and substantial risk of predation by diurnal raptors. One such variable was reproductive period. During times of high energetic demand for reproductively active females, the number of pre-sunset emergences increased four-fold. Roost population size and distance to forest edge also influenced emergence timing consistent with anti-predator tradeoffs. The emergence behavior of Indiana bats is thus consistent with a trade-off between energetic demands and the risk of predation, most likely due to the temporal overlap of early emergences with the activity period of diurnal raptors.;Chapter 3 addresses the possibility of moonlight avoidance in temperate-zone bats. Moonlight avoidance is commonly observed in small mammals and tropical bat species. However, such avoidance has rarely been noted in temperate-zone bats. To investigate this further, I used acoustic recording devices to quantify the activity of two bat groups in open powerline corridors running through forest. I examined the general activity of those two groups, as well as their tendency to avoid the moonlit side of a corridor. I created models using relevant environmental variables and compared them using an information-theoretic approach. Neither bat group showed a significant preference for flight in shade over light on full moon nights. Low-frequency bats, however, showed generally lower activity on full moon nights. The general activity of mid-frequency bats was predicted by reproductive condition, temperature and wind, although they also tended to avoid activity on full moon nights. These somewhat contradictory results may reflect the avoidance of flight near tree edges (i.e. in corridors) under bright moonlight, a location from which nocturnal flying predators (owls) could mount ambush attacks. This work provides some of the first clear evidence for moonlight avoidance in temperate-zone bats.;Chapter 4 addresses the topic of bat activity during the winter, a period in which hibernating bats are traditionally thought to be inactive. Most previous research on winter activity of temperate-zone bats has focused on activity within or near hibernacula, where bats are highly concentrated, and relatively easy to study. Very little research has been conducted on overall activity in open landscapes away from these hibernacula. Thus, I recorded bat activity across open landscapes over 4 winters, including multiple "normal" winters, and one extremely warm winter (Winter 4). Temperature was a main driver of activity in low-frequency bats. Nearly every period with above-average nightly temperatures was associated with activity. Bat activity was detected at every sampling site. Mid-frequency bats were either generally absent during much of the winter, or were less responsive to temperature increases. Mid-winter activity during the normally-coldest portion of the warm winter was surprisingly unaffected by the extreme warmth of Winter 4. However, the start of spring-like bat activity began approximately 6 weeks earlier than usual during Winter 4. Evidence from insect sampling suggests that mid-winter activity was not driven by feeding, but late-winter insect activity during Winter 4 may have supported feeding by bats. The overall results strongly suggest that mid-winter activity by bats in western Indiana is a surprisingly widespread phenomenon.