Bat Colony Social Patterns on Defense Lands

USGS Cooperative Research Unit Corner

Bat Colony Social Patterns on Defense Lands

Bat conservation and management is a tricky business. Hard to catch, count and track, most species' life history aspects, including those "relatively" well studied such as the endangered Indiana bat (Myotis sodalis), remain a mystery. For land managers in the eastern United States tasked with a myriad of stewardship responsibilities and multiple-use outputs, finding the right strategies to balance resource management needs with the needs of forest-roosting bats has been difficult. Often, the mere presence of Indiana bats or the discovery of a tree or snag hosting a maternity colony in the summer has meant substantial project modification, curtailment or abandonment to avoid direct take, especially on state and federal lands. The Virginia Cooperative Fish and Wildlife Research Unit, in collaboration with the U.S. Army Engineer Research and Development Center and the resource managers at Fort Knox, are working together to address questions about bats' resiliency to roost-loss. Specifically, they are looking to determine if combining knowledge about forest stand dynamics and the fission-fusion social strategy could be useful for developing novel and proactive ways to manage bats.

Forest stands with suitable day-roost conditions for bats are often readily identifiable with moderately to poorly stocked stands of species that have large amounts of exfoliating bark such as shagbark hickory (Carya ovata) or standing dead snags. These conditions are ephemeral on the landscape and follow particular regeneration or disturbance events. Research through the Virginia Cooperative Unit has shown that within these forest conditions, bats such as the Indiana bat or the Northern long-eared bat (Myotis septentrionalis) display fission-fusion social patterns during the maternity season. Female bats, depending upon their reproductive condition (pregnancy, post-parturition, volancy of young), may form large colonial aggregations in a few trees and then disperse through the season to more trees as smaller groups ? but with most periodically returning to specific core trees with their conspecifics. Hence, for land managers, with forest stands containing bat maternity colonies, understanding what trees are critical roosts, how those stand conditions arose, how resilient bats are to tree loss and/or how new roosts can be recruited into the future forest are paramount. On Department of Defense lands, endangered species and biodiversity management is a stewardship priority due to the uniqueness of the military mission and specific range needs, and the presence of Indiana bats, for example, can be a significant management issue. Moving bats on the landscape where they would not impact range needs could provide incredible flexibility to current management strategies.

Using the Northern long-eared bat as a surrogate, bat maternity colonies at Fort Knox have been identified and monitored by netting "Judas" bats over streams and waterholes and then radio-tracking them back to their maternity sites. Whole tree bat colonies are then netted, radio-tagged and monitored over the maternity season to determine the temporal and spatial nature of the fission-fusion dynamic and the characteristics of the trees and stands used. The research has shown that Northern long-eared bats display a complex social dynamic of association and tree use that varies spatially and temporally. Once the conditions were known at Fort Knox, central core trees, secondary trees, and combinations thereof were felled when bats were dormant in their hibernacula to gauge subsequent bat response in following summers. Also, adjacent to removals, trees in some stands were killed with herbicide to create standing dead snags as potential new bat roosts.

Post-removal monitoring found that Northern long-eared bats were somewhat tolerant of removal of their roosts and the spatial footprint of the roost areas shifted only slightly in the following year. The bats were adept at finding and using new trees locally (often suppressed sassafras Sassafras albidum with cavities created by heart-rot fungi and woodpeckers). But this was true only up to a point. Once removals exceeded 20-30 percent, single maternity colony networks started showing patterns of break-up with the original network still connected by only one or a few trees sharing a few individuals from what probably now constituted two socially separate groups. Concomitant to the work, Fort Knox, unfortunately became a White-nose Syndrome positive area, affecting the installation's Indiana bats and Northern long-eared bats. Although disappointing, its occurrence also allows this research to assess an additional component of how habitat conditions interact with disease impacts and hopefully future recovery for bats.

Insights learned at Fort Knox are now being used by the Virginia unit to help managers at Fort A.P. Hill, Fort Drum and Fort Pickett also understand how northern long-eared bats use forests on their installations and how forest management can be tailored to protect bats and improve habitat conditions. These efforts and research are particularly timely now that the U.S. Fish and Wildlife Service has proposed this species for listing as threatened or endangered.

Each month, 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.

November 17, 2014