Fat Bats and Thin Forests: A Conservation Conundrum

This article was originally published in the Winter/Spring 2024 edition of the South Park Heritage. This version has been revised with updated information as of July 2025.

Fungus Among Us

As the summer sun sets over the Mosquito Range, the aerial grace of chickadees and bluebirds gives way to a more acrobatic silhouette that dominates the moonlit skies. These shadowy figures belong to our allusive, misunderstood mammalian cousins - bats. 

Bats are deeply ingrained in folklore and popular culture around the world, often symbolic of death and darkness. For many, bats evoke images of vampires and a primal aversion to diseases like rabies. But unlike vampires, bats play a pivotal role in supporting the ecological health of our planet. Bats are among nature’s most effective pest control. A single half-ounce little brown bat (Myotis lucifugus) can consume over 1,200 insects in an hour, including mosquitoes and spruce budworm moths (Choristoneura freemani), while also pollinating plants and dispersing seeds. 

Unfortunately, unlike vampires, bats do not enjoy the benefit of immortality and currently face a threat so dastardly that it would cause even Count Dracula to quarantine in his Transylvanian castle. 

Little brown bat with WNS. Published by U.S. Fish and Wildlife Service Headquarters via Flickr.

In 2023, Colorado Parks and Wildlife (CPW) confirmed Colorado’s first case of white-nose syndrome (WNS). The disease was found in a female Yuma bat (Yuma myotis) at Bent’s Old Fort near La Junta. This news was devastating but not unexpected. 

WNS is a disease caused by the fungus Pseudogymnoascus destructans (Pd). Infected bats appear to have white fuzz on their nose and wings. Luckily, WNS does not pose a risk to human health, but it is often fatal for bats. First detected in New York in 2006, WNS has spread rapidly across North America, leaving millions of dead bats in its wake. Today, WNS has been confirmed in 40 states and eight Canadian provinces. 

As expected, WNS has rapidly spread in Colorado. In 2024, WNS was confirmed in Boulder and Larimer Counties. Earlier this year, WNS was detected west of the Continental Divide at the Holzwartz Historic Site in Rocky Mountain National Park in Grand County.

Body temperature of a bat without WNS (Graph B - top) versus a bat with WNS (Graph C - bottom) during the winter of 2008/2009. Spikes in temperature occur during arousals. The bat with WNS experienced more arousals and a sharp drop in body temperature before eventually dying. Source: Reeder et al. (2012)

Many bat species hibernate during winter, lowering their body temperature to conserve energy, called torpor. Every few weeks, bats briefly wake up from torpor, called an arousal. Arousals are energetically costly. WNS disrupts this normal cycle, threatening the life of its host. Like Dracula, WNS sucks the life out of bats. Dr. Tina Cheng, Director of White-Nose Syndrome Research at Bat Conservation International (BCI), explains: 

“While bats may spend over 99% of their time in torpor, they actually use 80-90% of their energy budget arousing from torpor… Bats are perturbed by this fungal infection on their skin, and they arouse much more frequently. [It is] estimated that they arouse twice as frequently as a healthy bat. Every time it’s waking up, it’s burning through critical fat reserves. This makes surviving winter much more challenging."

Pd can be found throughout Europe and Asia, where bats have adapted to the fungus and are less affected by it. When Pd arrived in North America, it found species without natural resistance, spelling disaster for our native bats, particularly little brown bat, northern long-eared bat (Myotis septentrionalis), and tricolored bat (Perimyotis subflavus). Populations of these species across the eastern US and Canada have experienced a greater than 90% mortality rate, with some populations becoming completely extirpated.

Nine of Colorado’s 18 known bat species call South Park home, including the little brown bat. Because of the vital ecological role they play, a significant loss of bats could hinder agricultural production and cause insect population booms that degrade forest health and disrupt the outdoor activities that make South Park special. WNS is expected to continue spreading throughout the western US and Canada in the coming years. 

Bat-ter Days Ahead

The outlook for these little critters is grim, but there is still hope.

There is currently no cure for WNS; however, results from vaccine trials show promising results. Even if a reliable vaccine is developed, the challenge of administration remains: it is a nearly impossible task to administer an oral or injectable vaccine to millions of individual bats across the continent, but it is a positive step regardless.

Natural evolutionary resistance offers a glimmer of hope as well. In the past few years, studies of east coast caves devastated by WNS have shown populations stabilizing and even rebounding to 5 - 30% of their previous populations! Bats that survive exposure to Pd have several genetic variations compared to conspecifics that succumb to the disease, meaning future generations will likely have an improved genetic resistance to WNS.

While it may be easy to sit back and let nature take its course, bat populations take 10 - 15 years to start showing signs of recovery. For us Coloradans, that means we may be swatting away more mosquitoes while hiking, fishing, camping, and hunting until our bats rebound in the 2040s.

Ecolocating a Solution

Bat conservation should be top-of-mind for homeowners and those who enjoy recreating in South Park. Fat bats are the name of this conservation game, urges Mylea Bayless, BCI’s Chief of Strategic Partnerships, “the healthier and the fatter the bats can go into hibernation in the winter, even if they encounter white-nose syndrome, the more likely it will be for them to survive.” 

However, bat conservation is not so simple because some of the actions we can take to support bats conflict with another critical conservation concern in the West - wildfire mitigation. 

Ponderosa pine (Pinus ponderosa) snag

Standing dead trees, also called snags, are important bat habitats. “During the summer, female bats are seeking the warmest settings to use as maternity roosts or nurseries, where they will give birth to and raise their pups,” says Dan Neubaum, Species Conservation Program Manager at CPW, “a good maternity roost ensures that the pups are kept warm while ‘mom’ is out foraging at night for bugs.” Research conducted by Neubaum found that little brown bats utilize aspen snags in the fall, “this scenario allows bats to maximize energy storage before tucking into rock crevices and talus slopes where they drop into deep hibernation for the long winter.” 

While snags are great for bats, they are also excellent fuel for wildfires. Fire is a natural process, but decades-long forest management policies have suppressed beneficial small fires, resulting in the uncharacteristic accumulation of dead wood and dense understory across western forests. This buildup of fuel invigorates larger fires that have many negative downstream effects. Hotter fires leave behind large burn scars with little vegetation and poor soil quality. Rainstorms on burn scars result in major flood events that cause sedimentation in streams, rivers, and reservoirs, decimating the water quality essential for living, farming, and recreating. To combat this, programs such as Firewise encourage homeowners to reduce fuels on forested properties. 

Fuel reduction and bat conservation may seem diametrically opposed on the surface, but  striking a healthy balance between the two can create a mutually beneficial ecological relationship. 

We can accomplish this in three steps: Safety, Snags, and Stewardship

Engelmann spruce (Picea engelmannii) with ladder fuels removed

Safety First 

The safety of your home, family, and community is paramount. Prioritize creating a defensible space around your home by eliminating combustible debris, such as leaves, vegetation, and firewood within five feet of structures. Clear dead wood, create gaps between trees, and remove ladder fuels (shrubs, immature trees, low branches, and other combustible material beneath mature trees) within 100 - 200 feet of structures. These actions are also recommended for managing natural boom cycles of spruce budworm, which are currently defoliating some of South Park’s forests.

Snags Second 

While removing fuels, consider leaving some snags: “My best advice would be clear the trees where you need to clear the trees for safety reasons and leave the rest”, advises Bayless, “let the forest decay naturally to the best of your ability. If you’re in a pine beetle outbreak where you have a lot to deal with, see if you can find a happy medium. Leave some for the bats. It will really make a big difference.” 

Neubaum echoes this sentiment: “[Land]owners can thin trees and leave some snags, particularly if the snag is situated within other live tree stands or live conifer and near riparian areas. These live trees will protect the retained snags from being blown down in high winds… The best snags for bats tend to be trees that are larger in diameter, have large vertical fissures, and exfoliating bark. To minimize wildfire risk, remove low branches and other ladder fuels beneath and around the snag.” 

Neubaum also encourages landowners to prioritize felling trees during winter months, “as bats are least likely to be using snags during this window… If cutting in winter is not possible, doing so in spring or fall can work as the bats tend to roost alone or in small numbers during these shoulder seasons versus the larger maternity colonies that form in summer.” 

Homeowners who prefer to remove all snags from their property or do not have a forested property can install a bat house to provide supplemental roosting habitat. Bat houses are especially encouraged within one-quarter mile of water bodies and wetlands. Bats prefer to stay close to water to drink and to indulge in the abundance of insects that water attracts. Creating roosting habitat for bats near water reduces travel time and energy expenditure as they move to and from their preferred feeding grounds, fattening them up for the winter. 

Remember, bats like to stay warm. In Colorado, bat houses should have a dark exterior and be installed facing south to maximize heat absorption. Houses should be installed at least ten feet above ground on a pole or structure, and at least 20 feet from tree branches to reduce depredation risk. Multi-chambered houses are preferable to single chamber designs.

Stewardship Third

The next step is supporting insect communities to help bats fatten up before winter. While reducing fuels, leave decomposing logs and stumps in place, especially if already inhabited by insects. Decomposition is a natural process that enriches soil and supports important native insects. This includes moths, one of bats’ favorite foods, as well as ants, beetles, and parasitic wasps that prey upon insects that can kill trees, like spruce budworm and mountain pine beetle (Dendroctonus ponderosae). 

Avoid using pesticides to control pest insects whenever possible. While pesticides are the most effective immediate control for budworm and pine beetle, pesticides do not target only undesirable species. Indiscriminate spraying kills many of the beneficial insects that feed bats and naturally control pest species. Therefore, pesticides are not recommended unless used to maintain select high-value or high-risk trees. 

White loco (Oxytropis serica) blooming where snags were cleared the prior year.

Encourage native wildflowers that attract pollinating insects. Forest thinning stimulates wildflower growth by allowing more light to reach the forest floor. Pulling noxious weeds like common mullein (Verbascum thapsus), Canada thistle (Cirsium arvense), and field bindweed (Convolvulus arvensis) reduces competition for wildflowers, allowing them to thrive. 

Those who enjoy more geologic recreational activities, such as rock climbing and spelunking, should be acutely aware of their potential role in spreading Pd. Always adhere to cave closures and restrictions, and ensure that all clothing and equipment used in or near caves or crevices that may house bats are diligently disinfected before exploring another location.

Lastly, help track the spread of WNS. Report dead bats year round and live bats observed during the winter to CPW by calling the Bat Hotline (303-291-7771) or sending an email to wildlife.batline@state.co.us. Cover dead bats with a box or bucket and keep children and pets away from the bat. Handling dead bats is not recommended, but if necessary, wear gloves and secure them in two plastic bags. Take photos of the bat, especially if it has a band on the wing or an antenna secured to the body, as these bats are being monitored. 

WNS is the stuff of nightmares for North American bats. There is no stopping it. However, a balanced and coordinated effort to promote bat and forest conservation in South Park will make a difference for thousands of these winged wonders and help build a resilient ecosystem for future generations to enjoy.