Improving Bat Houses in America:

Nearly 40 Years of Progress and Still Learning

By Merlin Tuttle


Bat houses are outstanding tools for education. When I introduced them to Americans in 1982, my primary objective was to help people overcome fear and accept bats as valuable neighbors. That goal has been vastly exceeded. Today, hundreds of thousands of American bats live in a wide variety of bat houses.

Individuals who have carefully tested local bat preferences, and adapted accordingly, are reporting close to 90 percent occupancy. Nevertheless, there is still much to be learned. And that is why we’re initiating new collaborations.

Late last month, local member, Debbie Zent, founder of Austin Batworks, reported an impressive event. Her three-chamber nursery house had been caulked, sealed, and painted inside and out, and was mounted high on a streamside ranch building—a nearly perfect combination. But to find it overflowing with occupants just days later was surprising.

This Texas Hill Country bat house became overcrowded within days by Brazilian free-tailed bats (Tadarida brasiliensis).
The house was ideally located approximately 18 feet up on a building beside a permanent creek where it receives only morning to mid-day sun.

Was this extraordinary success due to house or location quality, or were these bats simply desperate?

We are now working with Debbie to test the latest innovations in bat-rich areas, especially where previous attempts have failed. Additionally, we recently collaborated with Tom and Laura Finn, founders of Fly By Night, test three of their Deluxe Bat Condos that have peak-season capacity to shelter up to 1,000 bats each. Hundreds have been installed in Florida with 90 percent occupancy. Ours were mounted on poles near rivers. Additionally, Tom helped us mount three small houses on nearby buildings.

Tom Finn digging a 3.5-foot-deep hole for installation of one of his Deluxe Bat Condos overlooking Onion Creek, a few miles southwest of Austin.
Tom demonstrating how one person can use a tapered trench to install a bat condo on top of a 24-foot pole.
Dani Cordani, MTBC’s Bat House Project Coordinator, assisting Tom by adding water to concrete mix already in the hole. The bottom of the fully erected house is 17-18 feet above ground.
Tom explaining condo features, including metal roof, landing pads, sealed and painted surfaces throughout, and unique venting. More details to be available in MTBC’s forthcoming bat house resource.
Pedernales River habitat adjacent to our second condo location.
Tom and helpers inspecting the newly-installed condo at Westcave Preserve, also near the Pedernales River. Assuming occupancy, reserve educators hope to explain bats to visitors during evening emergences.

Tom demonstrating how to use a rope to lift a bat house after having climbed a ladder. This BatBnB two-chamber house has been altered with three-quarter-inch thick furring strips to provide extra roosting space between the house and building. This adds an additional roosting chamber at little cost (above, left). During installation, Tom braces the house on his ladder. This house will be shielded from rain but exposed to morning sun (above, right).

On a broader scale, Jay Gaderre, of WHITEHORSE, has agreed to help test a small bat house design that has proven more than 90 percent successful in Taiwan. Jay will be shipping samples for testing in five U.S. states.

Taiwanese schoolteacher, Heng-Chia (Thrash) Chang, invented an extraordinarily successful bat house that has approximately 90% occupancy.
Thrash mounted more than 100 of his unique bat houses at the grade school where he teaches. The school is now famous for its bats and attracts 20,000 visitors annually to its Formosan Golden Bat Museum. The students are almost continuously surrounded by bats wherever they go and not a single one has ever been harmed or contracted a disease.
Three mother lesser Asiatic yellow bats (Scotophilus kuhlii), each with one pup. Thrash’s small houses are very popular and have attracted 12 species when mounted on buildings. They don’t attract large bat colonies but are very popular because they are lightweight and easy to mount on a wall.
This is the only one of Thrash’s houses mounted on a tree at his school and it’s the only one that has never been occupied.

Why so much new testing? Haven’t we already learned all we need to know about bat house basics? Yes, between 1988 and 2004 we did learn a great deal through the North American Bat House Research Project, led by Mark and Selena Kiser and myself, relying on invaluable reports from thousands of volunteer participants.

Virtually all kinds of bat houses were at least occasionally successful. But the best-used houses were:

·        tightly constructed, caulked, and painted

·        mounted 10 to 25 feet above ground on buildings or poles

·        positioned to receive sun appropriate to local climates

·        roosting chamber widths of ¾ to 1 inch

·        sited within a quarter-mile of a stream, river, or lake

·        located in areas where bats were already attempting to roost on or in buildings

 Failures were strongly associated with:

·       warping due to poor materials or treatment

·        mounting on trees

·       vulnerability to predators (mostly climbing snakes or owls from nearby perches)

Initial results were mixed. Some users uniformly failed while others with similar houses were dramatically successful. As we’ve gradually discovered why, occupancy success has improved.

Temperature was identified as a key determinant. Bat houses could be too hot or too cool, or could simply fluctuate too much. For example, in coastal areas of the Northwest, bats readily occupied houses mounted on poles but rejected them east of the Cascade Mountains. Day-to-night temperature fluctuated too much in arid areas. This can be solved only by using extra-large houses or by mounting them on buildings which serve as heat-sinks that dampen day-to-night temperature fluctuations.

Except in areas of extreme day-to-night changes, pairs of houses mounted back-to-back on poles in full sun, one facing southeast, the other northwest, are increasingly favored by America’s most experienced bat house users. Testing can pay big dividends.

In Florida, Ernie Stevens hung a bat house from a tree limb and attracted a nursery colony of 124 apparently desperate evening bats. When I convinced him to try mounting a pair of houses back-to-back on a pole in full sun, his original colony moved to the house facing northwest and expanded to over 300. These were joined by free-tailed bats in the warmer southeast-facing house. His resulting mixed colony included 800 bats!


In Louisiana, Bill Halloway began by mounting two houses on pine trees. No bats were attracted, so he moved them to a pole, mounted back-to-back. Bats promptly began moving in. Encouraged, he added another pair of larger houses on a pole, one black and one white, and ended up with a mixed nursery colony of 800 free-tailed and big brown bats, apparently due to a greater range of temperature options.                

Much can be learned by simply watching bat house occupants on warm versus cool days.

In Pennsylvania, Lisa Williams and Cal Butchkoski noticed that their little brown bats moved up on cool days, down on warm, literally hanging their heads out on extra hot days. By adding ventilation slots, they were able to protect their bats from overheating, even in sun-exposed, black houses on the hottest days. Vents are now standard in all but the coolest climates.

As a result of such reported discoveries, the Kisers and I were able to publish the Bat House Builder’s Handbook in 1993. Over the subsequent 27 years discoveries have continued. Recently, Dani Cordani and I have been interviewing America’s most experienced bat house users in a wide variety of habitats and climates, each with decades of experience with hundreds of bat houses.

Based on their experiences, it’s clear there is still more to learn. We’re working on an updated resource that will:

  • summarize points of broad agreement
  • explain areas still in need of improved understanding
  • introduce longer-lasting materials and designs, and
  • provide detailed construction plans
Lisa Williams and her mentor Cal Butchkoski were among the first bat house pioneers in America. Here they are monitoring temperature in each bat house roosting chamber to determine effects of bat house shape and the positioning of ventilation slots.


If you’ve made a potentially important discovery, it’s not too late to share it with us at If you’d like to support these endeavors, please donate here and/or join MTBC as a sustaining member.

To better protect both bats and bat house consumers, MTBC is also offering our seal of approval to vendors whose houses meet our strict standards for construction and advice. Our resource, Selecting a Quality Bat House, provides guidance and a list of certified vendors. To apply for certification, contact

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Bat Flash! Misleading Article Harms Bats and Public Health

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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Exploring Ecuador’s Los Cedros Reserve

By Teresa Nichta

This rainy February, we visited Los Cedros Biological Reserve in Ecuador.

Roo Vandegrift, and crew, are filming Marrow of the Mountain; a documentary about the mega-mining now in Ecuador. “In 2017, the amount of land available for mining expanded by hundreds of percent, leaving huge swaths of Ecuador’s most sensitive and biodiverse habitats at the mercy of international mining interests. These concessions appeared suddenly and were sold without public knowledge or consent, especially affecting the mineral-rich and endangered Choco Rainforest.” Roo invited MTBC to conduct a bat survey, which could support litigation to stop the illegal gold mining and help protect the reserve’s unique flora and fauna. The data is to track diversity and endemism at Los Cedros, and analyses are submitted to conservation groups and government agencies, like Critical Ecosystem Partnership Fund and the Ecuadorian state Institute for Biodiversity (part of the Ministry of Environment).

Los Cedros Biological Reserve consists of 17,000 acres of premontane wet tropical forest and cloud forest. Of this, 2,650 acres is formerly colonized land, while the remainder is primary forest. The reserve is a southern buffer zone for the 450,000-acre Cotocachi-Cayapas Ecological Reserve, and both are part of the Choco Phytogeographical Zone. The Choco region is one of the most biologically diverse and endemic habitats on Earth.

Part of its charm is the journey to get there. Monica and I left our Quito AirBnB at 5 am to board a 3-hour long bus ride to Chontal, where we met Marc Dragiewicz of Eyes of the World Films. It was then just a short 30-minute truck ride to the trailhead. 

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49th NASBR in Kalamazoo, Michigan

The 49th Annual North American Symposium on Bat Research was held in Kalamazoo, Michigan on October 23-26, 2019. It was hosted by Amy Russell and Maarten Vonhofm amidst a quintessential Midwestern autumn. There’s no better place to keep up with the latest bat research technologies and discoveries or for graduate students to explore career options. Many of the researchers attend every year, developing lasting friendships and invaluable networking opportunities. Not surprisingly, this is Merlin’s favorite group. He hasn’t missed a meeting in 49 years. This year, Merlin joined Brock and Sherri Fenton and Price Sewell in presenting an enthusiastically received pre-conference workshop on bat photography.

Our hospitable hosts, Amy Russell and Maarten Vonhofm.

Merlin especially enjoys opportunities to encourage students in conservation-related careers and takes great pride in the achievements of those he has helped. Four joined Merlin for the organization’s annual “Lunch with a Mentor” program to discuss career path choices, conservation interests, and of course, to hear a few of Merlin’s wild adventure stories.  They also got a perspective from Teresa who sat in on the meeting. (Check out Advice for Young People Interested in Science and Conservation) (more…)

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A Model Example of Bat Recovery Potential

By Merlin Tuttle


Long Cave, in Kentucky, like many others, has a long history of human occupation with little record of prior use by bats. It was mined for saltpeter, a key ingredient of gun powder, during the war of 1812 and was subject to commercial tourism, probably beginning at about the turn of the century, ending by the 1930s.

Rick Toomey and Merlin Tuttle waiting for group to enter bat-friendly gate at Long Cave.


Huge passages trapped cold air and remained cool year-round, offering major opportunities for bat hibernation. Roost stains from past bat use were widespread, and the cave clearly had potential to shelter millions. As recently as 1947 some 50,000 bats, presumed to be largely the now endangered Indiana myotis (Myotis sodalis), continued to return in winter. Nevertheless, entrance barriers built to exclude non-paying tourists, increasingly restricted air flow, eventually culminating in a concrete wall and a nearly solid door. (more…)

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Thank You For Your Voice – Editors are Listening and Bats are Benefiting

By Merlin Tuttle

A reminder that our members DO make a difference! Leading news media outlets are changing tack, publishing more positive, and fewer negative, stories about bats as a direct result of MTBC members’ ongoing support and actions.

Your vigilance brings misleading articles to our attention. Your support enables us to carefully document and explain issues of concern. Your personal, diplomatic comments to editors influence their further actions. Media portrayal of bats cannot be ignored. It is key to broad public understanding and support, without which conservation progress could prove impossible.

The intermediate horseshoe bat (Rhinolophus affinis) ranges from northern India to southern China. It is one of the horseshoe bats speculated, but still unproven to have caused the SARS epidemic.

Since 2014, we’ve prepared and distributed 15 blog posts and 18 Bat Flashes providing counterpoint documentation in response to exaggerated, misleading, and often completely wrong speculation attempting to link bats to rare, but scary diseases. Widely distributed publications included “Give Bats a Break” in Issues in Science and Technology (subsequently translated into French and Chinese), “Fear of Bats and its Consequences” in the Journal of Bat Research and Conservation, and “Humans Shouldn’t Be So Scared of Bats” in Slate. Additionally, the science journal, Nature, published a co-authored response in its correspondence section, titled “Don’t misrepresent link between bats and SARS.” (more…)

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Experiencing Texas Bats

By Renee Anna Cornue

As MTBC’s Photo Collection Administrator, much of my responsibility lies behind a computer screen. I’d seen thousands (about 120,000 if we’re being real) of photographs from Merlin’s most-active field work days, preparing me for what to expect as much as photographs can. I’d seen mist nets, harp traps, banded bats, guano piles, and evidence of the bats’ incredible diversity.

Though fortunate to see Austin’s bats in a variety of ways, I’d never worked with bats first-hand. On this trip, I was most excited to step away from the desk and learn how bats are studied in the field, especially surrounded by knowledgeable and talented peers.

As with MTBC’s past adventures, our trip was a hands-on working trip with invaluable time and expertise contributed by leading colleagues from varied specialties. We were in the company of expert bat researchers, photographers, videographers, rehabilitators, consultants and passionate citizen scientists as we searched for some of the least known bats in the U.S.


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48th NASBR in Puerto Vallarta, Mexico

This was Merlin’s 48th and Teresa Nichta’s 1st NASBR.

The 48th Annual North American Symposium on Bat Research conference was held in Puerto Vallarta, Mexico October 24-27. Hurricane Willa threatened but failed to dampen the enthusiasm of attendees who ended up enjoying perfect weather in a beautiful location. Our hosts Jorge Ortega and Rodrigo Medellin did a great job, and we were very favorably impressed with the outstanding conservation orientation of Mexican colleagues. Mexico’s students had an unusual opportunity to present their projects, ranging from bat pest control in walnut orchards to seed dispersal and the pollination of agaves from which all tequila is derived. Additional areas of conservation interest involved impacts of wind turbines, management of white-nose syndrome, and protection of roosts.

Rodrigo Medellin welcoming colleagues to the 48th meeting of the North American Symposium on Bat Research.

Many attendees were delighted to see Merlin and meet Teresa and share insights on the needs of bats. Based on his 60 years of field experience, Merlin has become increasingly concerned to see so many of today’s remaining bats living in marginal, sometimes barely survivable conditions, especially in caves. These unfortunate circumstances easily can be misinterpreted as what bats need, leading to inappropriate conservation measures. He was encouraged to see rapidly growing awareness of the futility of stopping or curing white-nose syndrome, with increasing focus on protection of survivors from disturbance at roosts. Where bats were protected from disturbance, signs of stabilization and recovery were reported. (more…)

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Partnership for Bat Conservation and Management Training

By Merlin Tuttle

John Chenger and Julie Zeyzus interviewing Merlin for training video on bat cave management.

In early August, we accepted a partnership invitation to develop a series of bat conservation and management training videos. Though growing numbers of biologists are studying bats, few have the breadth of experience essential to meet their widely varying conservation needs. Each species has unique requirements. In order to better share my nearly 60 years of personal experience, John Chenger founder of Bat Conservation and Management, and Janet Tyburec founder of Bat Survey Solutions, invited me to collaborate. They are providing video shooting and editing, featuring my narration and illustrations.

Teresa Nichta (left) and Julie Zeyzus shooting slow motion video of Brazilian free-tailed bat (Tadarida brasiliensis) emergence.




Four programs are now being edited. The first, tentatively titled “Win Friends, not Battles,” explains key approaches that have most effectively won long-term cooperation. The second features the worldwide importance of bats. The third addresses greatly exaggerated disease claims, and the fourth deals with assessing cave suitability for bats and special long-term management needs.

Bad gate that caused abandonment by a large colony of cave myotis (Myotis velifer). New owners removed the gate, and the bats are now gradually returning.

Under John’s guidance, we began field shooting on August 15, greatly aided by Teresa Nichta and John’s associate, Julie Zeyzus. For the next 10 days there was little time for sleep or even eating. On my birthday, we spent seven hours filming underground, a great antidote for thinking of getting old!

Measuring roost stains left by a formerly large colony of cave myotis in a Texas cave. Stains can last for centuries, providing an invaluable estimate of past colony size.


Illustrating the need for such education, one of the caves we visited in a protected nature reserve, had lost its entire colony of tens of thousands of cave myotis when fire protection permitted entrance blockage by vegetation. Another cave, also well protected by its owner, had overgrowth of an invasive, introduced plant that could have prevented restoration of a formerly large colony. It only took minutes to eliminate the threat.





Videoing Brazilian free-tailed bats close-up in crevices between box beams.

Explaining how bat-friendly bridge designs have aided Texas farmers.

Sunset emergence of free-tailed bats.

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Bats and Chocolate Production

By Merlin Tuttle

While conducting her Ph.D. thesis research, Bea Maas and her team (Maas et al. 2013) collected data that would surprise even her. When insect-eating bats and birds were excluded from cacao trees in Sulawesi, Indonesia, the crop yield fell by 31 percent. And when she compared losses due to night versus daytime exclusion, bats versus birds, she discovered that bats accounted for 22 percent of the prevented losses.

A control site in the same study (poles without netting).

To obtain such data, Bea selected 15 plantations where she enclosed 120 cacao trees in 60 exclosures (like huge, mesh cages) constructed of nylon mesh. There were four exclosure treatments per plantation, one daytime, one nighttime, one day and night, and one always left open as a control.

A bat/bird exclosure in Sarawak, Indonesia, built with bamboo poles and commercial nylon monofilament netting with a mesh size of 2 x 2 cm. These were opened and closed like curtains daily.


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