Bat colonies roosting, flourishing thanks to artificial bark
April 19, 2013
Fort Knox has the largest known maternity colony of federally endangered Indiana bats in Kentucky and the second largest known colony in the species' range. During an emergence count in 2007, 282 individuals were observed emerging from a single maternity roost tree. This maternity colony has been monitored each year since its discovery in 2005 through the use of mist netting, radio telemetry, and acoustical surveys. In addition to monitoring, Fort Knox has initiated a project to augment summer roosting habitat through the use of artificial roosting structures which mimic the bats' natural roosts.
Indiana bats hibernate in caves and mines during winter; but in summer, roost, give birth, and rear their young under slabs of loose bark of primarily dead or dying trees. These natural roosts are ephemeral by nature, lasting only a few years; however, artificial roosting structures will have a much longer lifespan providing suitable roosting sites for many years, which is important because Indiana bats return to the same maternity area year after year. If proven effective, artificial roosting structures could be an important tool in the management of Indiana bats, as well as other imperiled tree-roosting bats.
The first maternity colony of Indiana bats discovered on Fort Knox (approximately 150 individuals) was in 1999 during a preconstruction survey conducted for the MultiPurpose Digital
Training Range and Northern Training Complex. As part of the mitigation measures set forth in the Final Environmental Impact Statement Record of Decision developed for the construction and operation of the MPDTR and NTC, Fort Knox established the 1,458 acre Indiana Bat Management Area to create and enhance existing bat habitat and to increase the population of Indiana bats.
The IBMA is situated in the northeastern part of the installation, immediately adjacent to the MPDTR. Management activities include timber stand improvement, invasive species removal, selective girdling of trees to create roosting sites, wetland management, and forest management to provide and enhance quality foraging habitat. Population monitoring also continues to be a part of the management activities in the IBMA, as well as on other portions of the installation.
In 2006, Fort Knox began installing artificial bark on standing dead trees in the IBMA near known maternity trees. The first iteration of bark installed was small Eco-shake® shingles (12 inches x 22 inches). Between 2008 and 2010, larger pieces of artificial bark (3 feet x 8 feet) were installed. Bats began using the artificial bark almost immediately; as many as 240 bats have been observed emerging from two of the trees. Mist netting confirmed that at least some were pregnant Indiana bats, indicating use as a maternity site; however little brown bats and one northern bat were seen as well.
During the artificial bark project, several roost trees fell down due to wind or natural deterioration. In an effort to create longer-lasting roosting structures, power poles pressure-treated only at the bottom to eliminate possible negative effects to bats, were placed in the IBMA and outfitted with artificial bark in 2012. The artificial roost trees should last many years providing quality roosting sites for Indiana bats and other species of tree-roosting bats. They also offer a certain amount of flexibility due to the fact they can be placed on the landscape in areas that may reduce potential conflicts with military training, which will be good for military readiness and for the conservation of bats.
While Indiana bats have been reported to use artificial roosts, mostly bat boxes, use of this scale is unprecedented, which is very encouraging. It offers another tool by which to manage this endangered species, as well as other bat species. While the use of artificial bark is encouraging, natural roosts are still very important, because Indiana bats switch roosts every two to three days during the summer. Research is currently being conducted in the IBMA to refine methods of producing natural roost trees through varying treatments of girdling and chemical injection. Forest management activities are also ongoing to improve foraging habitat. Fort Knox will continue to monitor the artificial roost structures in the IBMA and plans to install them in other areas of the installation where suitable summer Indiana bat maternity habitat exists.