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October 31, 2022

Bats play important roles in ecosystems around the world, but bat populations are at risk from disease, development, and more. USGS scientists are working to understand these threats and help develop tools to inform conservation and protect wildlife and human health.

In this episode of the USGS Ecosystems Mission Area Outstanding in the Field podcast series, we head to southern Florida to learn about one of North America’s most misunderstood - yet threatened - mammals: bats.

Enduring symbols of Halloween, bats have long suffered a spooky reputation. They’ve been accused of harboring vampiric spirits, entangling themselves in human hair and are often associated with witches and warlocks. Few other mammals seem to frighten us with so many misunderstandings. But bats, because of their echolocation abilities and dark-adapted vision, rarely fly into or touch people. In fact, they help people in many unseen ways, as they play essential ecological roles. 

“People often ask why we should care about bats, and evidence strongly suggests that bats are saving us big bucks by gobbling up insects that eat or damage our crops,” said Paul Cryan, a bat researcher with the U.S. Geological Survey. “It is obviously beneficial that insectivorous bats are patrolling the skies at night above our fields and forests, and these bats deserve help.” 

Halloween marks the end of Bat Week, an annual, international celebration of bats designed to raise awareness for bat conservation. Around the world and across the internet, scientists, conservationists, and bat enthusiasts of all kinds recognize the importance of bats. This month, Rep. Welch of Vermont introduced House Resolution 1446, which expresses support for the designation of the week of October 24, 2022, to October 31, 2022, as "Bat Week." At USGS, we celebrate bat science and all the ways our scientists are working to learn more about bats and the threats they face. 

Pollinating bat. Courtesy Ami Pate, National Park Service
Bats perform valuable services, including pollinating plants and crops. This bat is covered in pollen. (Credit: Ami Pate, NPS)

There are more than 1,400 species of bats, some the size of a human thumb and others with a six-foot wingspan. Most bats eat insects, many eat fruit and nectar from plants, some eat rodents, and yes, some consume blood. All are primarily active at night. Many species of bats rely on echolocation (locating objects by reflected sound) and incredible dim-light vision to navigate through the night and in the caves and tree-roosting sites they inhabit. During winter, many species of bats hibernate in cool and moist caves or mines. Hibernation is an adaptation for bat survival during cold winter months, when there are no insects available for bats to eat.

Unfortunately, white-nose syndrome (WNS), a fatal fungal disease of hibernating bats, has killed over six million bats since 2006, and may well lead to the extinction of certain bat species. Other threats to bats include habitat loss from land use change (e.g. urban and energy development and climate change. 

Read on to learn more about some of the threats to bats studied by USGS scientists.

An Invasive, Emerging Killer: White-Nose Syndrome

U.S. bat populations have been declining at an alarming rate since the 2006 discovery of WNS in New York state. To date, the disease has been found in 38 states and eight Canadian provinces and has killed more than six million bats. The Northeast, where bat population declines have exceeded 80%, is the most severely affected region in the U.S., although WNS is confirmed as far west as Washington state.

Image: Bat with White-nose Syndrome
This hibernating little brown bat shows the white muzzle that is typical of white-nose syndrome. (Greg Turner, Pennsylvania Game Commission)

“The high number of bat deaths and range of species being affected far exceed the rate and magnitude of any previously known natural or human-caused mortality event in bats, and possibly in any other mammals,” said Cryan.

WNS is caused by a deadly fungus called Pseudogymnoascus destructans. True to its ominous name, P. destructans, or Pd, causes a powdery white growth on the muzzles and wings of most infected bats (the telltale sign of a life-threatening WNS infection), wing damage, and abnormal bat behavior. One of the consequences of WNS is that the hibernation of many afflicted bats is interrupted, often causing them to depart their winter roost early and eventually starve to death. Recent USGS research has found that Pd infects bat skin in a manner unlike any other known mammalian pathogen, a discovery that led USGS scientists to hypothesize that Pd may have evolved from a fungus that infects plants. 

Image: UV Light Showing White-Nose Syndrome in Bat's Wing
Long-wave ultraviolet (UV) and white-light are used to illuminate lesions associated with white-nose syndrome. This wing from a tri-colored bat is lit from above with a hand-held UV flashlight. (USGS)

The disease is spread by bat-to-bat contact during hibernation, bat contact with a Pd-contaminated environment, and likely by humans carrying the fungus from infected caves to uninfected sites. While the disease typically spreads in the cooler winter months, when conditions are prime for fungal growth on bats, Pd can also spread during the summer months. Many caves in affected states have been closed to recreational use, and people visiting open caves are urged to follow specific decontamination procedures. WNS is not known to pose a threat to humans, pets, livestock, or other wildlife.

Imagery from temperature-sensing cameras suggests that bats who warm up from hibernation together throughout the winter may be better at surviving white-nose syndrome. (Paul Cryan, USGS)

The abrupt emergence and spread of WNS has impacted 12 North American bat species so far. There is no known cure for WNS, and diseases among wildlife are difficult to stop once they’ve become established in free-ranging populations. If the current rate continues, WNS could threaten several of these species with extinction, including the threatened Northern long-eared bat, two federally endangered species, the Indiana bat and gray bat. Just last month, the U.S. Fish and Wildlife Service proposed listing the tricolored bat as endangered. White-nose syndrome was identified as causing estimated declines of more than 90% in affected tricolored bat colonies and is currently present across 59% of the species’ range.

However, studies by USGS scientists and collaborators provide critical information about WNS, which is used by natural resource managers to help preserve ecologically and economically valuable North American bat populations. The USGS National Wildlife Health Center (Madison, Wisconsin) serves as the reference laboratory for WNS detections in the United States, analyzing one to two thousand samples each year from across the country.

The USGS National Wildlife Health Center is also investigating the use of a bat-specific vaccine to help immunize bats against the disease. A 2019 study led by that center demonstrated that bats vaccinated against Pd were less likely to develop WNS or die from the disease in two initial laboratory trials. Now, they are conducting field studies to study the efficacy of the vaccines in various conditions. 

To learn more, check out our new site about USGS research on white nose syndrome.

 Bats and Viruses that Affect People: COVID-19 and Rabies

A gloved finger gently moves toward a small bat, lying wings folded on a gloved hand, prompting the bat to fly away.
Like most wild animals, bats often don't appreciate being handled for research purposes. However when holding bats after handling and examination, they often appreciate the warmth and need a little push to go. This Western red bat was captured during USGS research to learn more about the ecology, distribution and movement patterns of western bats. 

Other diseases associated with bats are less of a threat to bats than they are to people. Though bats are at risk from white nose syndrome, in general, scientists have found that bats have super-human abilities of bats when it comes to dealing with microbes. COVID-19 and rabies, for example, are two viruses that USGS bat scientists are studying, but they don’t seem to be a major threat to bats themselves. Over the past few years, the USGS has led assessments on the likelihood for scientists and wildlife managers to transmit SARS-CoV-2, which is the type of coronavirus that causes COVID-19 in humans, to North American bats during fieldwork. Fortunately, their assessments to date have found that the risk of transmission from humans to bats during fieldwork is low and is further reduced with the use of personal protective equipment and testing. USGS research has found that Mexican free-tailed bats can be infected with the virus but don’t appear to spread it or become sick. The virus has not been detected in other North American bat species. These assessments are helping inform natural resource agencies as they determine the safety of research and management activities. 

USGS researchers are also studying rabies in bats. Most recently, researchers from USGS, the University of Wisconsin and the Centers for Disease Control and Prevention have been studying rabies transmission and the potential of vaccination for vampire bats in Latin America, where the common vampire bat is responsible for most rabies outbreaks in livestock. In August, they published results of a test of a rabies vaccine candidate for vampire bats. Although this vaccine did not improve survival rates for bats exposed to rabies, it did prevent viral shedding by rabid bats, which could reduce the spread of disease among bats and other animals.

Bats and Wind Energy

Wind energy is one of the fastest-growing sources of renewable energy in the U.S. today. Land-based wind turbines can reach more than 425 feet above ground with a rotor-swept area of one to 2.5 acres. 

Though wind turbines play an important role in the nation’s energy portfolio, bats and birds have been injured or killed from collisions with turbines and their massive turning blades. It is estimated that tens if not hundreds of thousands of bats die at wind turbines each year. As our nation’s renewable energy portfolio continues to grow, it is critical that development be guided by sound science so that infrastructure can be built in the best way and in appropriate places. USGS researchers are assessing why bats and birds interact with wind turbine blades at night and are investigating methods to reduce the numbers of bat and bird fatalities.

Bat approaching wind turbine GIF
(Credit: Paul Cryan, USGS. Public domain.)

The USGS is creating new applications of innovative technologies, like employing radar to track flight patterns of bats; using low-light surveillance cameras to discover underlying causes of bat-turbine encounters; developing models to predict wildlife fatalities; recording flight calls of bats and birds to determine the distribution of migrants in time and space; and experimenting with new ways of keeping bats away from wind turbine blades. For example, in one recently published study, USGS and partners put acoustic recorders on lighthouses to detect echolocation calls of tree bats along the Atlantic Coast. They then used the recording to develop a predictive tool to assess the probability of detecting bats under different conditions along the coast, a tool that could help inform planning for offshore wind. Another USGS research team recently wrapped up early studies into a method keeping bats away from wind turbines using “invisible” ultraviolet light.  Together, these efforts may help reduce the harmful effects of wind energy on bats by providing information needed for better turbine design, operation and placement. 

To learn more, please listen to this podcast on bats, birds, and wind energy, and browse through this USGS Story Map on wind power and wildlife.

Conservation Counts, and so do Partnerships

A map of bat diversity in the U.S.
This map shows bat diversity in the U.S. (Paul Cryan, USGS.)

Bats face many threats, but good data on the status of bat populations helps USGS track how bat species are faring and inform bat conservation. There are 47 species of bats in North America whose distribution and abundance are documented by the North American Bat Monitoring Program, or NABat. Established in 2015, this multi-national, multi-agency bat-tracking program, led by the USGS, is critical for evaluating potential impacts of the many stressors on bat populations. The program also helps managers determine bat conservation priorities and assess the efficacy of actions aimed at mitigating these impacts. 

In collaboration with its partners, the USGS uses data from bat surveys to understand how bats are distributed on the landscape and how their populations are changing over time in response to threats like white-nose syndrome. 

But the USGS can’t do it alone. More than 100 partner organizations contribute data to NABat, including U.S. state and federal agencies, Canadian agencies and provinces, Tribal organizations, military installations, nongovernmental organizations and private industry. Even the general public can be involved by engaging in community science. 

“The more standardized monitoring data we have, the better we can understand the health of our bat populations and the more useful NABat can be to informing bat conservation,” said Brian Reichert, a USGS scientist and the NABat program coordinator. “Efforts by NABat partners are invaluable.” 

New and old data and information gathered beyond formal scientific surveys are all useful to bat scientists and managers. Learn how you can get involved through the NABat Partner Portal.

Bat Colony
While mother bats are out foraging, the young bats huddle together in groups that biologists call a cuddle. (Alan Cressler, USGS)

More Information:

About Bats 

White Nose Syndrome and Bat Health 

Bat Migration and Wind Energy 

This story was originally published in October 2013 and last updated in​​​​​​ October 2022.



Click through the slideshow to see more images from USGS bat research.

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