Fall and winter activity of two bat species in response to winter flooding and decreasing temperature

Abstract

Mature trees with hollow cavities are an important resource as roost sites for Rafinesque’s big-eared bats (Corynorhinus rafinesquii) and Southeastern myotis (Myotis austroriparius). Southern populations of these bats typically remain active in the winter (ca. November-March) but seasonal flooding in bottomland forests may prevent them from exiting their roosts. Our objective was to determine if and how seasonal flooding affects activity and roost-switching patterns of these species in Cache River National Wildlife Refuge, Arkansas. In October-December of 2016 and 2017, we radio-tracked 21 Rafinesque’s big-eared bats and 17 Southeastern myotis to 33 and 42 confirmed roost trees, respectively. Tree species, cavity type (e.g., basal cavity), and GPS coordinates were recorded for each confirmed roost tree. Additionally, bat activity, temperature, and water level were monitored using acoustic devices, iButton data loggers, and gauges, respectively. Although both species remained active, some of their roosting habits changed in response to decreasing temperature (from ca. 30 ℃ to −6 ℃ at sunset) rather than flooding. Notably, Southeastern myotis used mainly water tupelo in the fall (86 %, n = 14 trees), but roosted in varied hardwood species located in adjacent floodplain forests in the winter. With adverse weather and higher water levels, behavioral changes exhibited by these species may coincide with changing priorities from foraging to avoiding seasonally rising flood waters, maintaining homeostatic balance, or breeding and social interaction. In conclusion, when creating or revising their management plans, managers will need to consider the variety of roosts that these species require at different times of the year.