Bat House Warnings – A Reality Check

5/6/21
Merlin Tuttle

Observations of heat-stressed, sometimes dead bats associated with bat houses, have led to unfortunate speculation that bat houses can become ecological traps that lure bats to their death. It is true that numerous bat houses are badly built and sold with unreasonable claims and little, if any, instruction on bat needs. Vendors of such houses defraud customers and threaten the credibility of bat conservation. Both vendors and customers can benefit from education and certification. Nevertheless, there is no evidence that poorly constructed bat houses threaten bat survival. Bats are smart enough to avoid bad bat houses except when desperate from lack of alternatives.

Loss of vast numbers of traditional roosts is a key cause of bat decline. Most species that occupy bat houses today originally relied on loose bark and cavities in snags that were often lost during storms. This likely explains why bats prefer to live where multiple roosting options are available.

Radio tracking studies show that occupants of natural roosts frequently move among several, apparently to escape predators and parasites or find optimal temperatures. During severe weather, large numbers may die even in traditional roosts. With so few remaining, bats often fail to find ideal homes.

When providing bat houses, the best way to reduce mortality is to offer a variety of roosting options. Several houses ideally should be colored, positioned, or vented to provide a range of temperature. Needs vary between cool versus hot weather extremes.

Selecting a quality bat house, as well as proper placement, are crucial to success. In our forthcoming book, Danielle Cordani and I will provide plans for houses that maximally meet bat needs over a wide range of temperature. However, a single house is unlikely to prove ideal for all species and locations.

Northern long-eared myotis (Myotis septentrionalis) emerging from beneath tree bark. Many bats roost beneath lose bark on old snags.
A nursery colony of Fringed myotis (Myotis thysanodes) reared young beneath exfoliating bark on this old snag in Arizona.

Where sufficient habitat exists, especially within easy reach of overwintering locations, available houses often become crowded, and growing numbers of young may perish for lack of available space. The same occurs at traditional roosts. We simply don’t see it. And we can’t prevent it, though careful monitoring and providing more bat house options can help.

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Saving Bats One Cave and Mine at a Time

4/23/21
Merlin Tuttle

Caves are a critical resource for America’s bats. But thousands are no longer available for bats. Early American settlers relied on saltpeter from bat caves to produce gun powder. Then caves became lucrative for tourism, and many others were buried beneath cities or flooded by reservoirs. Even caves that were not destroyed often were rendered unsuitable for further bat use. Not surprisingly, the most cave-dependent bats quickly crashed to endangered status.

Today, nothing is more important to their recovery than identifying, restoring, and protecting key caves of past use. At that, Jim Kennedy is an unsung hero. Early in his career he joined me in critical research on the needs of cave-dwelling bats and worked with master bat-gate-building engineer, Roy Powers, to become an expert builder.

Kennedy became an expert at detecting evidence of past use by bats, and he has helped build gates to protect many of America’s most important remaining bat caves. He has also led workshops to train others. In 2013, he founded his own company, Kennedy Above/Under Ground, LLC. His teams have built 56 protective gates at 43 caves and abandoned mines where hundreds of thousands of bats have since recovered from severe losses.

Illustrative of the impact of protection at key locations, endangered gray bats at Bellamy Cave in Tennessee, increased from 65 to more than 150,000 once protected. And when a bad gate was replaced at Long Cave in Kentucky, gray bat numbers grew from zero to over 300,000. At Saltpeter Cave in Kentucky, endangered Indiana bats increased from zero to 7,000 when poor gates were replaced, air flow was restored, and winter visitor tours were terminated. Jim was involved in restoring each of these caves for use by bats. 

Jim Kennedy (right) and endangered Indiana Bat Recovery Team Leader, Rick Clausen, documenting recovery of Indiana bats (Myotis sodalis) in Saltpeter Cave, Kentucky. The species began rapid recovery in this cave following installation of an improved gate and airflow led by Jim.
Heather Garland, Tennessee Nature Conservancy Cave Specialist, and Merlin Tuttle conducting a winter census of recovered hibernating gray bats in Bellamy Cave.
Bellamy Cave in Tennessee provides both cold and warm roosts permitting year-around use by endangered gray bats (Myotis grisescens). Dramatic recovery occurred following protection. A 100-foot-long, 10-foot-high, perforated steel fence ensures long-term protection. The bats chose to fly over the fence instead of through the gaps. Photo Copyright Jim Kennedy

Protection can be a real challenge. Even good gates, if wrongly located, can force abandonment partly because different species have unique needs. Gray bats, and other species that form large nursery colonies in caves, cannot tolerate full gates across entrances. Newly flying young slow down and become easy prey for predators. Jim has three ways of dealing with this. When a cave entrance is large enough, he leaves fly-over space above, relying on a perforated metal lip to prevent human entry. Alternatively, he sometimes builds a metal chute at the top, using perforated metal. When entrance size or shape precludes such approaches, he surrounds the entrance with a 10-foot-tall, perforated-steel fence. At Key Cave in Alabama, the Tennessee Valley Authority contracted Jim’s team early in 2021 to build a 390-foot fence that required 21 tons of steel. Its entrances were too small to permit young bats safe exit through gates.

This 390-foot-long fence now protects a nursery colony of endangered gray bats in Key Cave, Alabama. Photo Copyright Jim Kennedy
Jim Kennedy's crew unloading some of the 21 tons of steel required to build a fence to protect an important gray bat nursery colony at Key Cave in Alabama. Photo Copyright Jim Kennedy

Cave entrances on cliff faces can be especially difficult. At Bat Cave in Missouri’s Mark Twain National Forest, the U.S. Forest Service contracted Jim and his team to haul tons of steel and equipment up a cliff face to gate the cave’s two entrances.  A chute gate and a fly-over gate were necessitated to accommodate the cave’s gray bat nursery colony. For his success, Jim received a prestigious “Wings Across America” award.

In July 2020, Jim and his team encountered a new challenge when gating New York’s Barton’s Hill Mine. The 200-year-old mine includes miles of passages with multiple entrances at different levels, creating strong “chimney-effect” air flow. Though the gate was built in mid-summer, Jim’s team had to use a chain saw and jack hammer to remove ice that was blocking the work area. Then, despite summer heat, they were forced to wear snow mobile suits while working in a strong 38-degree Fahrenheit breeze exiting through the entrance!

This mine shelters the largest hibernating bat population in the Northeast, approximately 120,000 bats of at least four species. As bats have lost natural roosts in caves, abandoned mines have become increasingly important. In fact, they now shelter millions of displaced bats. This gate will protect both bats and humans. The ice-covered floor drops approximately 100 feet nearly vertically into a pool of water, a dangerous trap for the unwary. The Barton’s Hill Mine is now safer for both bats and people.

This chute gate was used to protect the second entrance to Bat Cave. Chutes allow quick and safe access for maternity colonies that are unable to use traditional gate designs. Photo Copyright Jim Kennedy
Bat Cave in Mark Twain National Forest, Missouri, showing difficult access. Tons of material had to be raised up cliff-face terrain using a pulley system. Protection of the cave's gray bat nursery colony required two kinds of gates. Photo Copyright Jim Kennedy
Builders constructing the first of two gates at Bat Cave in Mark Twain National Forest in Missouri. This gate employs perforated steel extending at right angles outward from the top to prevent visitors from climbing over while allowing bats ample fly-over space above the gate. Photo Copyright Jim Kennedy

Protection and restoration of traditional, but long-lost hibernation sites may be the single most important option for restoring bats, especially those recently lost due to white-nose syndrome. Loss of key caves has forced millions of American bats to seek alternative shelter in less suitable locations where inappropriate temperature, and sudden shifts, can increase both the cost of rearing young in summer and that of hibernation in winter. This makes them less able to survive the stress of higher metabolic rates and forced arousals caused by white-nose syndrome and human disturbances. Furthermore, as the number of suitable roosting caves diminishes, bats are forced to expend more energy on longer travel between summer and winter roosts, leaving less and less for emergencies.

Preparing to gate New York's Barton’s Hill Mine. Home to the largest remaining hibernating bat population of the Northeast. Work here was especially challenging. Large amounts of ice had to be removed before work could even begin, and workers had to wear heavy coats in mid-July. Photo Copyright Jim Kennedy
Heavy fog periodically created by cold air from the Barton’s Hill Mine. Photo Copyright Jim Kennedy

The value of protecting key cave roosts has already been proven for gray bats. When I began my conservation efforts on their behalf, nearly six decades ago, the species was in precipitous decline and America’s leading experts were predicting extinction. Today, due to the combined help of federal, state, and private organizations, volunteer cavers, and expert gate builders like the late Roy Powers and his protégée, Jim Kennedy, we have millions more gray bats than when their extinction was predicted. Nevertheless, additional cave-dwelling species, especially the endangered Indiana bat and little brown bat, remain in widespread need of help, and invaluable opportunities for restoration remain.

Welders progress at Barton’s Hill Mine. Photo Copyright Jim Kennedy
Jim Kennedy and his team pose at the completed Barton’s Hill Mine gate. Such gates have been extremely successful in protecting bats hibernating in caves and mines. However, identical gates are generally not tolerated by summer nursery colonies. Young bats must slow down to pass through, making them vulnerable to predators. Photo Copyright Jim Kennedy

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Inspiring Bat Conservation Through Photos

4/9/2021

By Teresa Nichta

The Bat Scan Project provides photo documentation, enabling a growing number of conservation projects and exhibits worldwide to share the values of bats. These photos are also heavily used in children’s books, school reports, and in both scientific and popular publications. For example, the Smithsonian’s book, BATS: An Illustrated Guide to All Species, exclusively relied on nearly 400 of Merlin’s photos.

We’re delighted to share a few highlights from recent use.

A Mexican long-tongued bat (Choeronycteris mexicana) pollinating agave flowers (Agave palmeri).
A California leaf-nosed bat (Macrotus californicus) catching a cricket.
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Comments on World Health Organization’s COVID-19 Report

The World Health Organization’s recent report on COVID-19 speculates a bat origin. However, its findings are seriously flawed and questioned by the Biden administration according to the Wall Street Journal. Former CDC Director, Robert Redfield, in his CNN interview, still believes it escaped from a lab in China. The origin clearly remains unresolved.

A review of scientific literature reveals that SARS-CoV-2, the coronavirus that causes COVID-19, has not been found in bats, and there are no reports of transmission from a bat to a human.

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Severe Weather Takes Heavy Toll in Texas

By Merlin Tuttle
3/2/21

Given overall warming trends, we weren’t surprised to see some 70 to 80° F days in January and February of 2021. But that hardly tells the full story!

Beginning on February 10th, historically low temperatures were recorded across Texas. For eight consecutive days (February 10–18), the temperature hovered between 37° and 9° F with six inches of snow on the ground in Austin, Texas. The first reasonable feeding opportunity for bats likely didn’t occur before the 21st.

The last similar event occurred 32 years ago in 1989. In a 9-day period (December 16–24) the daily temperature ranged from 51 to 4° F but remained below freezing for only two days versus seven in 2021. Fewer people were concerned in those days, but at least hundreds of killed bats were reported.

Brazilian free-tailed bats about to emerge from their day roost in a bridge crevice in Austin, Texas.

The recent event, Winter Storm Uri, created a disaster for overwintering Brazilian free-tailed bats (Tadarida brasiliensis). Encouraged by warming trends, more and more bats have remained in their summer roosts year-round instead of migrating south for winter. In recent years, hundreds of thousands have overwintered in bridge crevices of Central Texas, especially in the Austin area. Additionally, over the last four decades, an estimated 1,000 more annually have remained in Bracken Cave.

Unlike many other temperate-zone bats, Austin’s free-tails are not true hibernators. They do store fat in the fall and can survive for more than six weeks without feeding when roosting at 41° F. In Central Texas, they emerge and successfully feed when evening temperatures are 50° F or above, and in traditional winters they seldom would need to wait more than 10 days between feedings.

To survive for eight days with average temperatures well below freezing would be an extreme challenge. Bats have the largest surface area per volume of any warm-blooded animal, and active free-tails maintain body temperatures of roughly 102° F. Following the recent weather crisis, just warming up to go hunting was undoubtedly prohibitive for many, and it’s difficult to imagine that the insects the bats depend on for food would have been immediately abundant. Even though daytime temperatures averaged 78° F over four consecutive days beginning on February 21st.

Many concerned Austinites wondered why accumulations of dead and dying bats steadily grew through at least the 25th, despite the return to warm weather. The answer is two-fold. Many bats likely were still alive but too weakened to go hunting. Some of those may take a week or more to die. Also, those that literally froze to death could take weeks to fall from their roosting crevices. Tendons in their toes are designed to automatically lock the bats’ claws firmly to the roosting crevice until consciously released. Thus, a bat may hang in place long after its death

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Bat Flash! Help John Oliver Put Bats in Perspective

The Last Week Tonight with John Oliver February 15th episode shared misguided speculations about bats. Here is Merlin’s public letter to John Oliver. We don’t have his email address, so we’re counting on you to help get his attention. No shade, John, we understand the topic is muddy. We simply want the opportunity to set the record straight!

Contact information and action steps are listed below.

Dear John,

Given your reputation for integrity and fearless candor, several of your loyal followers have asked me to help you better understand disease risks from bats. Why me? Because, as one of the world’s most experienced bat researchers, I’ve handled hundreds of species worldwide for 60 years, often surrounded by millions in caves. I’ve also led successful conservation efforts internationally for more than 40 years. My experience and photographs are used worldwide, including in National Geographic articles, to share the truth about bats through my organization, Merlin Tuttle’s Bat Conservation. Here’s a clip from my appearance on David Letterman decades ago; I have been leading efforts to educate humans about bats my entire career.

I, and hundreds of others who study bats, have spent whole careers working with them unprotected against any of the so-called emerging diseases about which we’re now warned. And we’re still healthy. We’re also aware that millions of people visit and work in caves annually without causing disease outbreaks.

Thus, we question the sanity of warnings of extreme risks to visitors of tour caves where a bat could purportedly cause a deadly pandemic by defecating on them. There is no proof that such an event has ever occurred. And warning of the possibility is like warning of death from a falling spacecraft, possible but extremely unlikely.

I appreciate your mention of the far greater risks from industrial meat production and your comments on the essential contributions of bats to a healthy planet, but this is not enough to cultivate understanding and put risks in perspective. For the record, unlike rodents who are overpopulating due to the loss of predators, bats are extraordinarily vulnerable to extinction and already in alarming decline.

Exaggerated fear is the greatest cause of human intolerance and killing of bats. Unfortunately, sensational speculation, linking them to scary diseases, sells headline media stories and large grants. Virus hunting, typically linked to bats, has been shown to be an ineffective means of pandemic prevention. However, because bats are the easiest mammals to sample, and have few defenders, they have become tempting victims. Your guest failed to mention that, for anyone who simply doesn’t handle bats, the risk of contracting any disease from one is minuscule. In fact, millions of bats share cities with people from America to Africa and Australia without causing disease outbreaks. As our human population continues to expand, we inescapably must learn to live in harmony with nature.

Although well-intended, the following documented points are too often distorted or ignored in sensational media coverage. I’d be more than happy to assist you and your staff in balancing the story.

  • Bats harbor no more viruses than other animals 1.
  • Claims of disease from bats are often based on poorly supported speculation 2.
  • Claims of 96% genomic similarity between viruses are meaningless and misleading 3,4.
  • Promises that can’t be kept are misdirecting billions of dollars to virus hunting that is counterproductively biased toward bats and better spent on other health priorities 5,6, 7.
  • Bats have an undeniable history of living with humans without causing disease outbreaks 8.
  • There is a long history of lucrative, but exceptionally harmful, exploitation of disease exaggerations against bats 9.
  • Fear of bats leads to intolerance and killing 9,10.
  • Asking people to conserve bats because they are beneficial, while failing to counter exaggerated fear, is unlikely to improve conservation success 10.
  • Ebola was first speculated to come from fruit bats, then insectivorous bats, but more recently it was admitted that no source has been found despite extensive efforts 11, 12.
  • It cannot be stated strongly enough that Ebola, SARS, MERS, and SARS-CoV-2 have not been isolated from a bat despite frequent attempts.

Also, here’s a recent video sponsored by the U.S. National Park Service about putting bat fears in perspective. Thank you for your time, I hope to hear from you.

Kindly, 

Merlin

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Bat Flash! NatGeo’s “Virus Hunters” Spreads Groundless Claims About Bats

11/2/2020

By Merlin Tuttle

I viewed the National Geographic documentary series titled, “Virus Hunters,” with substantial disappointment. Warnings of growing reliance on bush meat and industrial farming were justified. However, coverage of wildlife too often exaggerated risks from bats. 

Bats are exceptionally easy to trap in large numbers, have few defenders, and are easily misunderstood. This makes them prime targets for scary speculation that is exceptionally lucrative in gaining media readership and unprecedentedly large grants. And unfortunately, the opinions of leading virologists who doubt that virus hunters can predict or prevent pandemics were left unmentioned.

The 2017 study that reported more viruses in bats than in other mammals sampled nearly twice as many bats as all other mammalian orders combined. Since most viruses have yet to be discovered, new ones can be found wherever we look. And because bats are an ancient group of mammals, it is not surprising that they sometimes host ancestors of modern species. 2020 study, concluding that bats harbor no more viruses than other animals, has been largely ignored.

Hundreds of thousands of Straw-colored fruit bats (Eidolon helvum) beginning their evening departure from a city park in Ivory Coast, Africa. Cities often provide the only homes safe from commercial hunters who sell them for people to eat. Despite such large numbers having lived in close association with humans throughout recorded history, they have not caused disease outbreaks. Their remarkable safety record casts grave doubt on recent speculation of their being dangerous carriers of disease.

Documented transmission of any disease from a bat to a human is exceedingly rare, and the risk is near zero for anyone who simply does not handle them. Hundreds of thousands of bats live in city parks across Africa. Yet there are no verified cases of Ebola transmission, despite huge efforts to find such an association. In fact, despite repeated assertions, there are no documented cases of Ebola, MERS, or SARS-CoV-2 viruses ever having been found in a bat, much less transmitted from a bat to a human. In truth, bats have one of the world’s finest records of living safely with humans. For example, in Austin, Texas countless thousands of visitors have safely viewed the spectacular emergences of 1.5 million free-tailed bats for decades without a single incident of disease transmission.

I have safely studied bats for more than 60 years, including publishing five articles in their defense in National Geographic. It is sad indeed to see bat survival threatened due to the same, traditionally respected, organization spreading groundless claims that bats can defecate deadly viruses by simply flying overhead. People seldom tolerate and often kill animals they fear, and none are more vulnerable than bats. Please, in your future coverage of Virus Hunters, put bat risks and benefits in perspective. The irresponsible spreading of falsehoods needs to stop.

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Bat Flash! Unveiling the Real World of Bats in a Time of Misinformation

9/15/2020

By Danielle Cordani

The avalanche of speculative reports associating bats with COVID-19 seems never ending. However, at a time of scary misinformation, bat researchers and conservationists worldwide are discovering new reasons to appreciate bats, some decades in the making.

In Central America, researchers from the Free University of Berlin analyzed communication between bat mothers and their pups. Just like humans talking to a baby, adult greater sac-winged bats (Saccopteryx bilineata) alter the “color” and pitch of their pup-directed vocalizations. Not surprising, this breakthrough indicates parent-offspring communication in bats is more complex than previously assumed. Further investigation of social feedback during vocal development in young bats may reveal even more shared language features between bats and humans.

A greater sac-winged bat (Saccopteryx bilineata) in Panama.

Across the Atlantic, a team of scientists in Africa used novel methods to describe more accurately the differences among bats. It turns out—as is common when studying bats—there is more than meets the eye. Comparison of the penis bones, echolocation calls, and genes of African vesper bats revealed three new species and two new genera. The discovery could mean new identification techniques for the often-indistinguishable group and clearer protections for unique bats and their ecosystems.

A banana pipistrelle (Afronycteris nana), showing its tiny size and one of its adhesive pads used for clinging to the inside of unfurling leaves.
Banana pipistrelles roosting in an unfurling banana leaf in Kenya.
Perhaps the most publicized bat discovery of 2020 was conducted by a group of scientists from Israel. Their groundbreaking study presents never-before-seen evidence of “cognitive mapping” in non-human animals. Using revolutionary tracking technology, Egyptian fruit bats (Rousettus aegyptiacus) proved extremely sophisticated and efficient at navigation. Bats relied on goal-directed memory maps rather than landmark cues or sense of smell, seldom foraging at random.

Despite great scientific advances, improved communication is needed to successfully interpret and share bat values with others. Douglas MacFarlane and Ricardo Rocha have taken this into account. By applying conversation psychology, they provide communication guidelines that can help neutralize negative associations between bats and disease. Even scientists with good intentions may inadvertently undermine their message by failing to debunk misinformation.

Falsehoods and fear are easily created through misunderstandings. For example, in Iran and the Mediterranean, myths of mercury-containing “bat nests” began circulating over social media, inciting needless environmental destruction. In response, Iranian researcher, Dr. Hossein Zohoori, teamed up to create Mercury Mirage, a powerful documentary that discredited the untruths with stunning visual evidence.

We congratulate all who are persevering in unveiling the real world of bats in times when investigation, attention and resources have been so severely misdirected toward disease speculation. Discoveries of bat sophistication and values, and effective communication, have never been more important.

An Egyptian fruit bat (Rousettus aegyptiacus) pollinating a baobab flower in Kenya.
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Timely New Children’s Book

9/3/2020

By Merlin Tuttle

Life Upside Down

Australia’s Grey-headed flying-foxes

Leading wildlife photographer and conservationist, Doug Gimesy, has teamed up with award-winning media graphic artist, Heather Kiley, to produce an outstanding introduction to the upside-down world of grey-headed flying foxes. Through stunning photography, simple text, and eye-catching design, this book provides a timely introduction to some of the world’s most frequently misunderstood and intensely persecuted animals.

Victims of misunderstanding and mass eradication attempts, Australia’s flying foxes now survive only as tiny fractions of former numbers. Forest clearing has left them homeless and starving. Countless thousands have been killed in mass shooting campaigns, electrocution grids, and flame thrower attacks on their roosts, known as camps. Remnant survivors are now forced to live in cities where they are needlessly demonized as carriers of dreaded diseases, despite a long history of living safely with people or subjected to attempts of forced eviction with nowhere else to go. Welcomed honeybees, dogs, and especially humans are far more dangerous! Moreover, large numbers of flying foxes are essential to reforestation and the survival of much-loved animals such as koalas.

Readers of Life Upside Down will be introduced to the real world of flying foxes as safe and invaluable neighbors and learn how they can be helped. This full-color, large-format, 48-page book is available in hardcover for $19.95 at Australian Geographic or at Book Depository.  

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Bat Flash! Misleading Article Harms Bats and Public Health

7/17/2020

By Merlin Tuttle

A disappointing number of authors and publishers are spreading the false narrative that bats are exceptionally high-risk sources of deadly viruses. The July 12 edition of The Washington Post contained an article titled, “Why do bats have so many viruses?” The author, Rachel Ehrenberg, was apparently unaware of the most recent analysis of viral risks.

We urge Rachel and other Washington Post journalists to review Mollentze and Streiker’s April 28, 2020 comprehensive analysis, published in the Proceedings of the National Academy of Science. Their paper titled, “Viral zoonotic risk is homogeneous among taxonomic orders of mammalian and avian reservoir hosts” concluded that bats are no more likely than other animals to host disease.

Virus hunters have focused search efforts disproportionately on bats, apparently because bats are exceptionally easy to sample in large numbers and have few defenders. Referring to the Covid-19 outbreak, Zhang and Holmes concluded that surveillance of coronaviruses in animals other than bats is critical to protecting against future outbreaks.

Sensational speculation, exaggerating bat association with scary viruses, has led to a serious bias that impedes our understanding of viral pandemics and creates a perfect storm of media publicity. This feeds into our broader academic crisis—the misallocation of large grants for splashy, attention-getting “research” that promotes career advancement over high-quality, reproducible scientific investigation. Such bias threatens to misdirect limited public health resources and halt, or even reverse, decades of conservation progress.

It’s time publishers, authors, researchers, and decision-makers let go of the premise that bats are uniquely dangerous sources of disease and end biased sampling and unsupported speculation. Instead, we need to identify true sources of human infection and insist on accurate reporting that leads to actual prevention.

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