For decades, the Indiana bat (Myotis sodalis) has been imperiled. Until recently, population declines were associated with disturbance of caves where the small, insectivorous species hibernates during winter or to summer habitat loss from deforestation and development. Then, in 2006, white-nose syndrome (WNS) was discovered in Albany, New York. The fatal disease is caused by a fungal pathogen, Pseudogymnoascus destructans, which invades the soft tissues of hibernating bats, disrupting torpor and dehydrating infected individuals. WNS has since spread to 33 states and seven Canadian provinces, killing more than six million bats along the way. Eleven North American species have been infected, including the Indiana bat, and researchers have been unable to slow its spread. Meanwhile, range-wide Indiana bat populations continue to decline, with current estimates at their second-lowest in more than 30 years.

While disease ecologists attempt to combat WNS, management efforts have increasingly focused on summer habitat in hopes of maximizing reproductive success and slowing WNS-related declines. In spring, female Indiana bats migrate from winter hibernacula to form summer maternity colonies beneath the loose bark of dead trees. Roost trees provide protection from predators and the elements, but more importantly, they supply ambient heat that’s essential for gestation and early development of juveniles. These colonies rely on a network of roosts, often more than 20, and individuals switch trees every few days. Therefore, large tracts of appropriate roosting habitat that are readily available across the landscape may be needed to conserve this species. This is especially true for infected bats that are likely to emerge from hibernacula already weakened from WNS.

To better understand summer habitat requirements and the drivers of maternity roost selection, the Missouri Cooperative Research Unit partnered with U.S. Fish and Wildlife Service to examine maternity habitat selection on National Wildlife Refuges (NWRs) in northern Missouri. The three-year project captured female and juvenile Indiana bats with mist nets and tracked them to maternity roosts using radio telemetry. Used roosts were then compared with unused but suitable trees to determine which characteristics drive selection.

Researchers tracked 23 individuals over two seasons, and 21 previously-unknown roosts were identified. In addition to confirming broad-scale habitat associations noted by previous studies, such as a preference for bottomland hardwood forests in close proximity to water, the latest study revealed major differences in primary (≥ 30 bats) and alternate (< 30 bats) roosts. The former are known to occur in tall, large-diameter trees with direct solar exposure, but there’s been less focus on characteristics of the latter. Preliminary results from this study indicate that alternate roosts are located in smaller trees with dense canopy cover, and weather data revealed a correlation between high temperatures and the use of these roosts. This suggests that individuals may select alternate roosts to avoid overheating in highly exposed primary roosts, emphasizing the importance of smaller interior snags to the health and survival of maternity colonies.

The current study also noted that more than half of the 21 roosts were located in American elm snags. This is unsurprising as Dutch elm disease has decimated populations throughout the eastern half of the U.S., resulting in an abundance of available elm snags. However, if Indiana bats in the region rely heavily on this species, maternity colonies may become vulnerable in the future as elms become less common across the landscape.

Results from this study will provide public land managers with valuable insight into habitat selection and assist recovery efforts for this endangered species. Better understanding drivers of habitat selection may allow managers to anticipate future obstacles, prioritize specific habitats, assist efforts to promote new habitat, and guide future land acquisitions. Notably, this research highlights the importance of smaller, interior roost trees during periods of extreme weather and the reliance of Missouri colonies on tree species that are likely to become less common on the landscape.

The ONB features articles from Cooperative Fish and Wildlife Research Units across the country. Working with key cooperators, including WMI, Units are leading exciting, new, fish and wildlife research projects that we believe our readers will appreciate reading about. This article was written by Dane Smith, graduate research assistant with the Missouri Cooperative Fish and Wildlife Research Unit.