Winter Prescribed Fire and Litter-Roosting Bats

Burning on warmer days and during afternoons could promote bat survival

by Sarah Farmer, SRS Science Communications
Some bat species such as the eastern red bat roost under leaf litter for short periods of time during the winter. Photo by billy liar, Creative Commons.

Some bat species such as the eastern red bat roost under leaf litter for short periods of time during the winter. Photo by billy liar, Creative Commons.

Rather than hibernating in caves, some bat species in the southeastern U.S. get through the coldest parts of winter by roosting under fallen leaves, twigs, and other dead plant material on the forest floor. Although this leaf litter protects bats from the cold, it could also put them at risk of being injured or killed by prescribed fires.

“Prescribed fires are often conducted in winter, which minimizes the risk to ground-nesting birds, reptiles, and other animals,” says Roger Perry, a U.S. Forest Service Southern Research Station (SRS) scientist. “However, burn crews frequently observe bats being flushed from the leaf litter during winter burning, and these observations led us to ponder the potential effects of winter burning on litter-roosting bats.”

A study led by Perry, a research wildlife biologist at the SRS Southern Pine Ecology unit, and published in the International Journal of Wildland Fire, offers some recommendations for managers conducting winter prescribed fires in areas where bat species roost in forest floor litter.

Litter-roosting bats enter torpor, which means that their body temperatures drop and their metabolism slows. Bats may be in shallow or deep torpor, and the colder it is, the deeper the torpor. “Bats in deep torpor take longer to arouse and respond to potential dangers,” says Perry. “However, bats in shallow torpor are able to escape more quickly from approaching flames.”

Perry and his colleagues established 64 study plots in the Ouachita Mountains of Arkansas. Personnel from the Ouachita National Forest conducted the prescribed fires, which were generally low intensity. Researchers measured temperatures below the leaf litter just before and during the prescribed fires. Across all the plots, the average maximum temperature during burning was 558o F and ranged from 50o to 1323o F.

Although scientists are not sure exactly what temperatures are lethal to bats, Perry and his colleagues estimated that bats could survive temperatures as high as 140o F as long as these temperatures lasted less than a minute. Based on this estimate, if bats were unable to escape approaching flames, they would have survived in only 5 percent of the study plots.

Just before the arrival of fire, the average temperature below leaf litter was 67o F. “Apparently, leaf litter warms up pretty well on clear afternoons during winter, and these warmer temperatures keep the bats in shallow torpor during this time,” says Perry. “Studies suggest that fire cues, such as smoke, may cause these bats to arouse from torpor, and these warmer temperatures allow bats to arouse quickly and escape.”

Because bats in deep torpor would take longer to arouse, they could potentially be killed in the fire. Therefore, conducting prescribed fires during the warmer periods of winter and during afternoons, when bats are likely to be in shallow torpor, could promote bat survival while still

improving wildlife habitat, consuming hazardous fuels, and providing the many other benefits of prescribed fire.

Read the full text of the article.

For more information, email Roger Perry at

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Posted in Fire, Fish & Wildlife, National Forests, Restoration

Managing Forests to Conserve Bat Populations Affected by White-Nose Syndrome

New Forest Service General Technical Report available

by Anna Walker, SRS Science Communications Intern
A tri-colored bat, an eastern North American bat species heavily impacted by white-nose syndrome. Photo by Roger Perry, U.S. Forest Service.

A tri-colored bat, an eastern North American bat species heavily impacted by white-nose syndrome. Photo by Roger Perry, U.S. Forest Service.

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


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Can Urban Forest Settings Influence How Well Children with Autism Manage?

U.S. Forest Service researchers collaborate on unique grant program

by Zoё Hoyle, SRS Science Communications
Grant Park in Atlanta. Photo by Scott Ehardt, courtesy of Wikimedia Commons.

Grant Park in Atlanta. Photo by Scott Ehardt, courtesy of Wikimedia Commons.

In late July, USDA Agriculture Secretary Tom Vilsack announced the four recipients of the 2016 USDA Forest Service’s National Urban and Community Forestry Challenge grants. One of the four, the winning proposal from Georgia State University (GSU), investigates the impact of natural environments such as urban and community forests on symptom expression in children with autism spectrum disorders (ASD).

Brian Barger, research assistant professor at GSU, is principal investigator for the grant, with collaborators from other universities, nongovernmental agencies, and the Forest Service Southern Research Station (SRS). Cassandra Johnson Gaither, project leader of the SRS Integrating Human and Natural Systems unit based in Athens, Georgia, and Annie Hermansen-Baez, SRS science delivery and Kids in the Wood coordinator in the same unit, will provide their expertise in assessment and technology transfer.

“Research results showing the positive effects of managed natural environments such as urban parks and forests on human general and mental health have grown exponentially over the last decade,” said Barger. “Yet no studies to date have explored the effects of these environments on the expression of core and associated symptoms in children with autism spectrum disorders.”

In a unique experimental design, the researchers will combine census block-level data on tree canopy cover from the National Land Cover Database with comparable data from the National Survey of Children’s Health, which includes questions of parents of children with ASD about the severity of ASD symptoms associated with anxiety, intellectual functioning, learning, and attention. Researchers will conduct multiple analyses to explore the association between canopy cover from managed natural environments and the severity of the symptoms of children with ASD reported by parents.

Project researchers will also conduct experimental studies at sites in four different states – Arizona, Colorado, Georgia, and Nebraska – where children with ASD will participate in activities designed to induce cognitive fatigue followed by walks in canopied forests or parks. Cortisol will be measured from the participants’ saliva to provide data on the anxiety and stress levels in the children, and an executive functioning test will follow each full session. Results will be compared with those from the same exercises conducted in non-canopied conditions.

In addition to these exercises, SRS scientist Johnson Gaither will conduct qualitative interviews with parents at the Georgia sites to add data about the participants’ social and physical environment. “We’re particularly interested in the family structure of participating children and their parents’ attitudes towards nature and the managed natural environments we’re studying,” said Johnson Gaither. “We’d like to know if and how parental attitudes influence stress responses in their children.”

The data from the project will be used to provide insights for groups who want to work with children with ASD in managed natural environments. SRS science delivery expert Hermansen-Baez will help develop a “Lessons Learned” document for nature centers, camps and other groups seeking to develop programming for children with autism. The core “Lessons Learned” document and related materials will build on the project’s studies with added insights from nature site staff, research psychologists, special education specialists, and forestry experts towards creating and maintaining the best urban forest and park environments for managing symptoms in ASD children.

“We plan to design a printed booklet with tips for working with children with autism,” said Hermansen-Baez. “These will be distributed at professional meetings, to boards of education and other community-based nature and disability groups, and to local, state, and federal parks. We will also share key findings and recommendations from the study through other youth-friendly outlets such as the Forest Service’s Natural Inquirer, as well as through the partners’ respective communication outlets.”

For more information, email Cassandra Johnson Gaither at or Annie Hermansen-Baez at

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Posted in Ethics & Values, Restoration, Urban Forests
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