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In March 2016, scientists found bats infected with white-nose syndrome (WNS), a fungal disease that’s killed millions of North American bats across the eastern United States, in Washington state, over 1,000 miles from the nearest confirmed infection site in eastern Oklahoma.
Because most bat species in the U.S. eat phenomenal numbers of insects, bats are important to agriculture and to forests and forest health, providing billions of dollars’ worth of forest and crop pest-protection each year. Since its discovery in the United States in 2007, WNS has spread quickly, making managing forests to conserve bat populations more important than ever.
For a recent general technical report published by the U.S. Forest Service Southern Research Station(SRS), SRS wildlife biologist Roger Perry and researchers at Virginia Tech and the U.S. Geological Survey compiled a literature review on the effects of common forest management techniques such as prescribed burning, timber harvest, and tree thinning, on three of the bat species in the eastern U.S. that have been highly impacted by WNS.
“Bats can be highly influenced by structural changes in forests,” says Perry. “With populations of many cave-hibernating North American bat species in serious decline due to WNS, understanding how forest management affects day-roost and foraging ecology of bats is currently a paramount conservation issue.”
As detailed in the report, while northern long-eared, Indiana, and tri-colored bats vary in terms of social behavior, roosting habitats, and foraging activity, each of these WNS-affected species can benefit from forest management that promotes diverse forest landscapes with multiple species of trees of mixed ages and with areas of both open and dense canopies.
Roosts, where bats live when they are not out searching for food, often differ between summer and winter. In the winter months, these three species hibernate in caves and abandoned mines, where WNS can infect and kill them. However, from May to October, they roost, forage for food, and give birth in forests, either in foliage, in tree cavities, or under loose bark of live and dead (snag) trees.
“It’s important to consider that bats probably don’t select their summer roost trees based on any one roost characteristic, but rather on the overall characteristics of the tree, the forest stand where that tree is located, and the landscape surrounding that tree,” says Perry, “On the larger landscape, foresters can bolster bat populations by managing lands with bats in mind.”
For example, based on previous studies, northern long-eared bats prefer to roost in cavities of snags – dead trees – and forage in uncluttered, open forests. They also roost frequently in previously burned areas and forage in partially harvested or thinned forests.
Endangered Indiana bats also use snags, but prefer to roost in trees larger than surrounding trees, especially shagbark hickories, and in forests with plentiful gaps in the canopy. As with northern long-eared bats, burning and timber harvesting can improve roosting and foraging opportunities for Indiana bats by creating snags and more open forests for foraging in the summer months.
Tri-colored bats, however, roost in dead leaves or needles of trees in unharvested forests close to water sources. In previous studies, tri-colored bats were unaffected by burning, but most strongly preferred roosts in forests with a hardwood-dominated midstory. Although the tri-colored bat has historically been one of the most abundant bats in eastern forests, surprisingly few studies have looked at how it uses forests.
Although these three species each have different roost and foraging preferences, they are all greatly threatened by WNS and could benefit from targeted forest management tactics. The report concludes with examples of management practices that could be implemented to improve roosting and foraging habitat for these bats, which could help mitigate the damaging effects of WNS. These practices include:
- retaining snags for roosting habitat, especially those snags larger than 20 centimeters (around 8 inches) in diameter;
- removing trees primarily during the dormant (winter) season when bats are not roosting in trees;
- installing artificial roosts near water sources if roosts are otherwise lacking in the area;
- retaining some mature trees during timber harvest, especially those with cavities, defects, or hollows that could offer roosting spots for bats;
- reducing timber harvest and prescribed burns during the pup-rearing season of June and July;
- creating diverse forest landscapes by thinning trees in some stands to create a variety of overstory and midstory densities while maintaining canopy cover over water sources; and
- protecting caves and abandoned mines from disruption during winter hibernation periods.
For more information, email Roger Perry at rperry03@fs.fed.us.