Selecting a Quality Bat House

By Merlin Tuttle

A bat house fully occupied by little brown myotis (Myotis lucifugus) in western New York. This is one of seven that Lew and Dorothy Barnes mounted on their barn. Combined, they held more than 1,600 bats prior to the arrival of WNS. Since 2013 50-70 have remained.

Ever since I first introduced the idea of attracting bats to American yards in 1982, one of the most frequently asked questions has been, “Where can I purchase a good bat house?” The next, of course, is “How do I know bats will come?”

Over decades of time we’ve learned a great deal about bat preferences, and in fact today, quality bat houses, properly located, are achieving close to 90 percent success. But the biggest problem has been finding reliable vendors who’s bat houses truly meet bat needs. Far too many purchasers have become discouraged due to failure of cheap, poorly constructed houses, or even good houses sold with inadequate instructions.


Characteristics of a Quality Bat House

  • Most temperate-zone bats prefer roosting crevices 0.75” wide. Wherever you live, several species likely will prefer this spacing. A few may prefer up to 1.5” crevices. These mostly include just three species. The endangered Florida bonneted bat (Eumops floridanus) lives only in central and southern Florida. Big brown bats (Eptesicus fuscus) are frequent bat house users throughout most of North America and are often found in 1 to 1.5” wide crevices. Pallid bats (Antrozous pallidus) occur in arid and semi-arid areas of the West, from southern Canada through much of Mexico. Multi-chamber houses that include one or two of the wider roosting crevices may appeal to the most species.
  • Taller houses provide the best thermal options. This is especially important in single-chamber houses (best at least 20” tall).
  • Tight fit construction, with all seams caulked, reduces leakage and warping that leads to abandonment.
  • Best resistance to weathering and warping is provided by houses with a UV-resistant plastic outer shell. However, wooden houses can be highly successful and long lasting if treated with a water-based sealant or three coats of paint. Houses that remain unsealed or unpainted often become warped and uninhabitable within 2-3 years. A water-based sealant is best for landing areas. Paint can render surfaces too smooth for secure footing.
  • All exterior parts of wooden houses ideally should be at least 0.5” thick. Any plywood used should be exterior grade.
  • All interior surfaces and landing areas must be roughened enabling bats, especially young, to gain secure footing. One-sixteenth-inch deep horizontal grooves at 0.5” intervals are ideal. Hand-roughened (scratched) surfaces or high quality, tightly-fitted screen also work well.
  • All bat houses should have a roughened landing area extending at least 4” below the entrance, with one exception. Multi-chamber houses permit an ideal option. By extending the roughened surface of the back to extend approximately 4” below the roosting partitions and permitting the sides, back and front to also extend approximately 4” below the roosting partitions, a recessed landing area can be provided. This ensures ideal protection against owl attack during entry.
Georgia pecan grower, Frank Biben, became organic after attracting thousands of Brazilian free-tailed bats (Tadarida brasiliensis) to his orchard. The tin roof protects from mid-day sun in a hot climate, while dark sides enable heating early and late in the day. Both large and small bat houses can be successful as long as the bats’ basic needs are met, i.e. appropriate crevice width and roughness, temperature, and security from predators.

Choosing a Size

As bat house quality and knowledge of preferred mounting locations, have improved, size has become less important. Many single-chambered houses are now successful when mounted on buildings. Houses with two or more chambers are most likely to attract nursery colonies. When a bat house is being provided as a new home for a colony about to be excluded from a building, it should be large enough to shelter the number of bats being excluded.

An early bat house study showed that people who provided two or more houses were twice as successful, possibly because most crevice-roosting bats are accustomed to living in snags or beneath loose bark, both of which tend to unpredictably fall, potentially leaving occupants homeless. Knowing there are options nearby appears to increase attractiveness.

Before purchasing a house designed to shelter thousands of bats, it is best to experiment with smaller two to four-chamber houses. If they succeed, larger houses are nearly always successful.


Where Bats are Most Easily Attracted

Mixed habitats near fresh water, such as lakes or rivers, are ideal. Areas where bats have attempted to live in buildings are also extra successful. Not all bats roost in crevices. However, crevice roosting species are typically the most abundant nearly everywhere, including at least 10 species that occupy bat houses in North America. Wherever you live there is a reasonable chance of attracting bats.


Where to Mount Bat Houses

This successful pair of bat houses, mounted on a pole in Texas, is shielded from mid-day sun by a metal roof, so it doesn’t over heat even though painted a dark color. Pole-mounted houses seldom work well in cold or highly variable climates. In such areas bat houses should be placed on buildings which can help stabilize temperature.

Outer walls of buildings are the best mounting sites for small houses and are the only locations likely to succeed in arid areas or cold climates. Buildings act as heat sinks, stabilizing temperature. In addition, bat houses in cold climates should be dark brown or black and positioned to maximize solar heating.

In more moderate and tropical climates, bat houses do very well on poles, ideally at least 12-15 feet above ground.

All bat houses should be in sunny areas, even in hot climates. There is a strong preference for dark brown or black houses in the coldest regions, with lighter-colored, well-vented houses, preferred where it is hot.

A North American study revealed that bat houses mounted on trees are least successful and take, on average, twice as long to attract bats even when successful. Bat houses on tree trunks are typically more shaded and may also be more vulnerable to predators.

Bats fear owls and climbing predators, probably at least one reason why it is best to keep bat houses at least 20 feet from the nearest trees. Nearby perches may help owls to sit and wait for bats to enter. Young ones are a bit slower and risk being pounced on. In warm climates, pole-mounted houses may require snake guards like those used to protect purple martins.


When to Expect Occupants

Where needs for homes are extreme, even poorly designed bat houses sometimes attract first occupants within just a few days. Two to six months is closer to average, and some very successful houses have taken years to gain first occupancy. Early occupancy is generally more common in locations where bats have already experienced bat houses. Some extraordinarily successful houses, especially extra-large ones, have taken 2-3 years or more to succeed. In all cases I am aware of, the largest houses take the longest to attract their first occupants, though those I’ve been involved with have eventually attracted thousands, in one instance hundreds of thousands.

Bat house owners in America are increasingly participating as citizen scientists in bat counts to document status trends since huge losses due to white-nose syndrome. This family’s bat houses once sheltered more than 1,400 little brown myotis (Myotis lucifugus). Now they’re documenting the species’ gradual recovery from just 50 in 2015 to 152 in 2018.

If you know you have a good bat house mounted in a good location, be patient. There is no evidence that adding bat guano will attract bats faster. Bats will likely arrive eventually. If an unoccupied house isn’t receiving at least seven hours of direct, daily sun, it may need to be moved prior to achieving success.


A roughened landing area, combined with recessed roosting crevices, permits bats to enter quickly with minimal exposure to predators such as owls. Bat house provided by Bat Conservation and Management, Inc.


MTBC-Approved Bat House Vendors

The following retailers meet most of my criteria for bat house success and longevity. There are likely others providing quality houses, and we would be happy to consider adding them to our list once they pass our inspection. To seek approval, please ship a sample of the design you would like approved (including instructions) to:

Merlin Tuttle’s Bat Conservation
5000 Mission Oaks Blvd., # 41
Austin, TX 78735


Approval, acceptance, or rejection will be within seven working days. Submitted houses and their accompanying information will be donated at local fund-raising events.




Bat Conservation & Management

Habitat for Bats


We invite suggestions and feedback on your experiences.

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A Big Step for Bats

Merlin Tuttle

Today’s issue of TheScientist contains another outstanding example of how MTBC is making a unique, but critical difference for bats. This article was originally submitted as an email to the editor. On January 13, I explained the harm done by biased portrayal of bats. The editor promptly requested permission to publish my communication as an op-ed. We encourage our members to share it broadly. Nothing can threaten bats more than the fear and intolerance created by misleading disease stories.

Rousette fruit bats are essential pollinators and seed dispersers. They form colonies of many thousands in caves and abandoned mines where they are extremely vulnerable to extermination. Tens of thousands were killed at a single site in Uganda by humans overreacting to fear of Marburg virus.

Speculation linking bats to scary diseases has become lucrative, both in generating research grants and media readership. As historically documented, it can have devastating impact in fostering intolerance and even massive bat eradication. It also threatens the credibility of scientists and publishers and diverts critical public health funding from far higher priorities.

Many authors and publishers of such counterproductive speculation are well intended, just misinformed. If kindly approached with sound documentation of the harm being done, they are appreciative and can be extremely helpful as we have repeatedly demonstrated.




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Young Conservationist Makes a Difference

Young Conservationist Makes a Difference

Anyll Markevich is a young man with a mission. He writes to Merlin, “I became interested in bats thanks to your book, The Secret Lives of Bats. It is one of my favorite books, and I have recommended it to more people than I can count! I have always known bats were cool, but not to the extent I discovered in your book. I want to be a wildlife biologist or ethologist when I grow up, so your book easily fascinated me.”


Anyll is far more than just interested. He’s also busily helping bats. He has written letters to editors in response to our Bat Flashes but wanted to do more. Using photos from our photo gallery, he designed his own bat brochures which he handed out to people at a local pedestrian mall. However, people were preoccupied with shopping and didn’t seem too interested.


He then emailed Merlin for advice on how to build bat houses that would best accommodate bat needs in the mountain climate of Colorado. He built nine, keeping one for himself, and sold seven to raise funds he donated to MTBC to help bats. But, being a very inventive 14-year-old, he passed his $100 gift through his father, who’s company matched his funds dollar for dollar through American Online Giving Foundation.


Lacking an ideal location for his bat house, he had to mount it a bit low, late in 2016. By the next summer, he found his first occupant. This year, Anyll and his mom noticed several bats flying around their yard for the first time. He checked his bat house and counted up to five. They’ve now left for winter, but he’s optimistic that he has the beginning of a colony. He’ll soon contact his customers, each of whom received instructions and one of his brochures. He’s hoping to hear of further success.


In his most recent communication, Anyll reported, “There is an exciting new development! Our local library (Boulder Public Library) wants me to build a four-chamber nursery bat house.” Furthermore, he got to meet professor Rick Adams, a well-known bat researcher and fellow conservationist from the School of Biological Sciences at the University of Northern Colorado. Rick will be consulting on placement of Anyll’s bat house, making Anyll very proud! His next objective is to convince the librarians to permit him to provide his brochures to interested library users.




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Bat Flash! Action Needed for Durian Pollinators at Risk

The durian is considered the king of fruits throughout Southeast Asia, but it can’t be produced, even in orchards, without bats to pollinate its night-blooming flowers. This important crop could be lost without better appreciation of the key contributions of bats and their habitat needs.

It’s time to give these bats a voice. Rimba’s media statement: Deforestation for Durian Plantations Poses Serious Long-term Risks to Industry’s Productivity and Profitability calls others to action on behalf of durian pollinators. The Star recently published an article, Durian farmers pay the price in the end, highlighting Rimba’s work, reaching more than 7 million unique visitors.

Malay Mail published another supporting article, Weighing in on bats and durians, which boasts over 3 million unique visitors not including the printed version.

The Rimba news release emphasizes the serious impact of deforestation-driven durian expansion to all relevant parties. They call on the Ministry of Agriculture and Agro-based Industry, the Department of Agriculture, the wider durian industry, and individual durian farmers to “think long-term and pursue good agricultural practices for growing durian that is sustainable, contributes to healthy ecosystems, and provides a future for the Malaysian durian industry and Malaysian durian lovers.”

The overall objective of their plan is to promote coordinated action worldwide to safeguard wild and managed pollinators and promote the sustainable use of pollination services, which are vital to both ecosystems and agriculture. We are delighted to see Rimba’s efforts on behalf of bats and the economies they support getting this well deserved attention. Let’s use our voices to amplify the message!



Our combined voices can make a difference. Choose any or all means of contact to reach out to The Star and Malay Mail editors to thank them for sharing this important reporting in your own words. Editors do take notice. Remember, your response can be very simple such as, “I greatly appreciate your support of bats and protection of sustainable durian production.” Editors just need to know you like or dislike an article in order for you to have impact. It’s numbers that count. Bats need all of you!


A cave nectar bat (Eonycteris spelaea) pollinating durian flowers. Durian fruits sell for billions of dollars annually in SE Asia, but flowers must be pollinated by bats in order to set fruit. Cave nectar bats and their larger flying fox relatives are its primary pollinators. These bats traditionally formed large colonies in caves but are in alarming decline in most areas, often overharvested for human consumption or killed during careless limestone extraction. This, combined with deforestation, poses a direct threat to durian production, as well as to a variety of other important products.

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Batman Returns

Last week, Merlin returned to his favorite institution of science, the Milwaukee Public Museum, where he spent his first 11 years as a young scientist (1974-86). He served as Curator of Mammals, with outstanding freedom to study and photograph bats, often funded and assisted by museum donors and volunteers, especially Verne and Marion Read and their family. Merlin resigned his position there in 1986 in order to devote full-time to the conservation of bats. He last spoke there some 15 years ago, but was still remembered and welcomed “home” by an extra large and enthusiastic audience despite having to compete with an important Green Bay Packers football game. Anyone who knows Wisconsin is aware that competing against the Packers is never easy!

Merlin’s much loved and never-to-be-forgotten Milwaukee mentors, Verne and Marion Read making friends with flying foxes in Australia.

His talk, titled The Incredible World of Bats, was a part of the museum’s Science on Tap Speaker Series, introduced by Mitch Teich, Executive Producer and Co-host of WUWM Milwaukee Public Radio’s “Lake Effect” program, who also interviewed Merlin on the show.

Merlin dedicated his talk to the  memory of Verne and Marion Read, who funded and participated in many of his earliest research and conservation initiatives, and continued to support his conservation efforts for decades even after his departure from Milwaukee. We especially enjoyed the generous hospitaltiy of our Milwaukee hosts, Ross and Mary Read, who along with brothers, Sandy and Tom, continue to provide much appreciated support for MTBC.

The museum takes great pride in its large, open-air dioramas that integrate natural history and anthropology. In fact, the world’s first diorama is still on display.


A gentle reminder of why Merlin prefered to spend winters studying bats in tropical climates.


Enjoying the museum’s butterfly garden!

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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.

Danielle Cordani, Vice President of the newly formed Bat Association at Texas State University, discussing her poster on bats at wind turbines with Merlin while Association President, Jacob Rogers, listens.
Teresa enjoying hotel flowers while Shahroukh Mistry, Associate Program Director, greets Merlin in background.
Canadian, Melissa Donnelly, explains her poster on Cuban bats.
Co-host, Rodrigo Medellin, shows off a freshly caught free-tailed bat.
Participants engaged in lively discussion at the annual Diversity in Science Breakfast.
Rodrigo leading strategic planning discussion, setting research priorities for lessor long-nosed bats (Leptonycteris yerbabuenae) in Mexico.
Dia de los muertos, Day of the Dead, celebration of the world’s extinct bats, prepared by Canadian, Charles Francis. This multi-day event in Mexico is a national holiday focused on remembering and honoring friends and family who have died.
Merlin congratulating Rodrigo on his outstanding conservation leadership in Mexico and throughout Latin America.


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PechaKucha with Batman

PechaKucha [ or ペチャクチャ translated as “chit-chat”] is a series of 6-minute talks from presenters in the creative industry including artists, musicians, architects, filmmakers, writers, entrepreneurs, and local personalities. Each presenter showed 20 images, each lasting for just 20 seconds. PechaKucha events foster the art of concise presentations.  This year’s PechaKucha Night Austin #32 was held in Austin on October 11, 2018. Merlin was honored to be invited by Austinites DJ Stout and Lana McGilvray, the hosts of PK ATX.
The following ten speakers each had 6 minutes to promote a subject in their area of expertise. Merlin, of course, promoted bats with emphasis on those in Austin and had an outstanding response. Watch his presentation!
  1. Herman Dyal – Graphic Designer/Architect
  2. Gretchen Harries Graham – Educator
  3. Dave McClinton – Graphic Designer/Artist
  4. Refugee Is Not My Name (Aaron Weiss, Jess Archer and Ashley St. Clair) – Art Collaborators
  5. Brian Beattie – Musician/Producer
  6. Dale Whistler – Artist/Sculptor
  7. Sarah N. Evans – Activist
  8. Randal Ford – Photographer
  9. Merlin Tuttle – Batman
  10. Mélat Kassa – Musician
Check out those bats! Beautiful poster made by Pentagram design firm.

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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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Counting Free-tailed Bats in Bridges

By Merlin Tuttle

Merlin inspects Brazilian free-tailed bats (Tadarida brasiliensis) moments after removing them from their bridge crevice roost for counting.

For many years we’ve wondered just how many Brazilian free-tailed bats (Tadarida brasiliensis) could cram into a single 18-inch-deep bridge crevice. Accurate counts of large colonies are difficult no matter how they’re made. However, when estimating bridge colonies, it would help if we knew the number, using an average horizontal foot of crevice.

The solution seemed easy. Two years ago, Glen Novinger, an MTBC member and I, inserted two, three-quarter-inch-thick wooden frames, each encompassing a square foot of interior space, into bridge crevices of the same width while the bats were out feeding. The idea was to later slowly remove them, forcing those roosting inside to exit into a cloth-lined bag from which we would count them.

However, the bats were full of surprises. The first night we waited patiently till half an hour after we’d seen the last ones leave—or at least that was what we thought! But when we approached to install our devices, roughly half remained inside. I couldn’t help but wonder how many emergence counts had missed those that, for whatever their reasons, didn’t emerge at sundown. (more…)

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Bat-Friendly Bridges Help Farmers

Merlin Tuttle

Building bat roosts into highway bridges in farmlands can benefit farmers at little or no cost to taxpayers. Mark Bloschock, a supervising bridge design engineer at the Texas Department of Transportation, discovered the potential for bridges to help bats when he worked on Austin’s now famous Congress Avenue Bridge. As hundreds of thousands of bats unexpectedly moved in, he contacted me for advice. He soon discovered that, by simply making small adjustments in the spacing between box beams, large numbers of bats could be attracted where needed, and where they weren’t wanted, they could be discouraged by simply changing the spacing.

In 1998, when highway US 90 required two new bridges over Seco Creek, near D’Hanis, Texas, he wrote specifications that placed the box beams three quarters to 1.5 inches apart, hoping to attract Brazilian free-tailed bats (Tadarida brasiliensis) to this important agricultural area. The bats quickly moved in and soon exceeded half a million, today as many as two million.


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