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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Timely New Children’s Book

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

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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Costa Rica’s Bat-Friendly Hotel

By Paula Tuttle

Merlin and I recently spent an especially productive week promoting bat conservation at the Harmony Hotel in northwestern Costa Rica. Merlin’s lecture, introducing the many values of Costa Rican bats, attracted a large and enthusiastic audience that included both hotel guests and community members.

Thanks to the owner’s passionate commitment to a healthy, sustainable environment, the hotel is a wildlife oasis in the midst of the small town of Nosara. Wherever possible, a lush profusion of native vegetation has been restored or introduced, serving as a magnet for animals, from howler monkeys, coatis and margay cats to large iguanas and an impressive variety of bats.

We quickly recorded more than a dozen bat species, belonging to five families, and introduced them to appreciative staff and guests. In fact, the proximity of multiple species posed the biggest challenge to use of a bat detector. The hotel may soon attract even more bats, as it intends to put up bat houses.

We were especially encouraged to learn of all the hotel’s progress toward environmental sustainability while maintaining top quality. The staff were outstanding. The food was healthy and delicious, and we thoroughly enjoyed the two evenings spent introducing the owners’ family and friends to the diverse array of bats found in their own yard.

Merlin has prepared a program on Costa Rican bats for the hotel to share with guests and in local schools, and we look forward to further collaboration.   

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Thai Adventures Part 4: Khao Chong Pran


By Merlin Tuttle

For me, our trip highlight was the visit to the Khao Chong Pran Cave in Ratchaburi Province. Nearly 40 years ago Buddhist monks who owned the cave had asked my advice. Their monastery relied on bat guano fertilizer sales for support. But in 1981 production was plummeting. Of course, and the monks wanted to know why.

Merlin and Surapon reminiscing about their first visit to Khao Chong Pran Cave nearly 40 years earlier.

Before dawn the next morning, my then young field assistant and interpreter, Surapon Duangkhae, and I discovered poachers using large fish nets to capture bats at the cave entrance. They were selling them to local restaurants. We hired two of the poachers to help us document the extent of the problem, then advised the monks to hire a game warden to protect their bats.

Merlin answering game warden’s questions in 1989.
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Thai Adventures Part 3: Cave Bats


By Daniel Hargreaves

We arrived at sunset at the OurLand Nature Reserve in Kanchanaburi Province, our home for the next 5 days. We quickly set up a few mist nets and a harp trap and were rewarded with a brace of lesser false vampire bats (Megaderma spasma) and several cave nectar bats (Eonycteris spelaea). Merlin took the opportunity to show the group how to train a bat. Unfortunately, the chosen bat was unusually difficult. However, just over an hour later it eagerly permitted Merlin to approach, enticing it to drink from a syringe filled with sugar water.

The next morning, we climbed 200 steps in search of roosting bats located in two caves above a monastery occupied by Buddhist shrines.

Group climbing the steps to the cave with Kate in the lead.
Group entering cave.
Daniel Hargreaves showing the first tiny bumblebee bat to our group.

Initially, we captured a long-winged tomb bat (Taphazous longimanus) but as the group was looking at that one, I netted two bumblebee bats (Craseonycteris thonglongyai). Both were females weighing around two grams. They were delicately held by group participants while I explained the species’ anatomy, ecology, and conservation status.

Mindy excited to be holding a famously tiny bumblebee bat.
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Bat Flash! COVID-19 Coronavirus Leads to More Premature Scapegoating of Bats

By Merlin Tuttle
Updated 03/26/20

The source of human exposure to the COVID-19 virus, or as it was first called, Wuhan virus, according to the March 12th edition of The Conversation, has yet to be identified. However, in a rush to judgment, far too many public health officials and media outlets are focusing almost entirely on bats. This has been seen in multiple news sources, from CNN to Vice. Such speculation can be counterproductive, especially when acted on as fact.

Bats, despite their essential ecological and economic roles, rank among our planet’s most rapidly declining and endangered animals1. They have few defenders and are often mistakenly viewed as dangerous. People who fear bats are less tolerant and frequently kill them 2.

Fear is needlessly created when virologists emphasize potentially distant evolutionary relationships that shed little light on where and how a virus is actually transmitted to humans. Bats are currently believed to harbor more kinds of viruses than other mammals. But even if true, there is no credible documentation of higher risk of transmission3. Most viruses are innocuous or even beneficial 3,4.

Bats, like any living organism, are capable of harboring scary viruses, yet transmission is rare, typically only to humans who carelessly handle a bat that bites in self-defense, followed by failure to seek medical attention. Nipa virus, in India and Bangladesh, is acquired by drinking unpasteurized palm juice, eating unwashed fruit, or associating with sick pigs5.

For more than a decade, virologists have used increasingly sophisticated technology to disproportionately search for new viruses in colonial bats6. New viruses can be found by looking no farther than our own human bodies, and they’re all related at some level4! We’re 96 percent genetically identical to chimpanzees7.

Scientists at Singapore’s Bioinformatics Institute examined a key surface protein on the COVID-19 virus and found it just 79 percent genetically similar to SARS, noting that these viruses “are like comparing a dog and a cat.” 8 This flies in the face of widespread claims of similarity.

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Thai Adventures Part 2: Flying Foxes


By Daniel Hargreaves

Several hours after leaving the painted bat village, we arrived at the Wat Chantaram, Buddhist temple, in Ang Thong province. The monks protect Lyle’s flying foxes (Pteropus lylei) in the courtyard. We explained the ecology and diet of the species and how the group should approach the colony to minimize disturbance. Slowly approached, most of the bats remained calm allowing us to watch them grooming as they prepared to depart for the evening. The bats steadily increased their activity and their chattering became louder as they started to fly out in all directions, leaving the temple grounds in search of fruiting or flowering trees. As the bats were leaving, we could hear the monks chanting inside the temple providing a magical backdrop to the evening.

Lyle’s flying foxes (Pteropus lylei) in Jantraram Temple courtyard, protected by monks in Thailand.

The following morning, we headed to Bang Pahan village in search of a second Lyle’s flying fox camp (a colony roosting site). The bats had set up camp alongside the river and after several attempts we discovered a spot where we could get closer.

Our focus was on photographing these roughly four-foot wingspan bats as they flew among roost trees. These weren’t as well protected, and something had made them nervous. They had a right to be, as some had wing membranes were perforated with holes from apparent shotgun pellets. Our group looked in awe as hundreds of these flying giants took to the sky, moving farther along the river.

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Thai Adventures Part 1: Painted Bats


By Daniel Hargreaves

Following a 6-hour road journey from Bangkok we arrived at our first destination, the painted bat village. With only two hours left before sunset, we split into two teams. One assisted Merlin with setting up the flight studio. The other went to find a painted bat to photograph in the studio that evening. Team two headed out in carts pulled by two-wheeled tractors. They quickly spit into small groups furiously searching the dried leaves of banana plants for bats. 

Riding in carts pulled by two-wheeled tractors to find painted bats.

It wasn’t long before we found a single male painted bat (Kerivoula picta) hanging in a dried leaf about a meter from the ground. The bat had been banded for research, so although a good candidate, we didn’t disturb him and continued our search for more. Less than 200 meters away we found another male this time without a band. We quickly checked his weight at 4.6 grams (less than the weight of a U.S. nickel) and decided he was a perfect candidate for flight cage training.

This one was carefully placed in a soft bag, and to ensure picture and set authenticity we took the bat and the leaf he was roosting in back to the village. (There was no shortage of such leaves.) Leanne Townsend balanced precariously on the back of a moped, holding the bat and set material, as it sped to the village in order to setup for the night’s photography. As our Thai hosts prepared a banquet for their guests, Merlin got to work on the set, helped by an enthusiastic group of members fascinated to watch the master at work. As soon as the set was ready, we fed and watered the little star and released him into the studio. The group looked on as his shallow wing beats resembled that of a butterfly. He investigated every corner of the studio until he was sure there was no easy escape, then entered his now relocated roost.

Photo: Daniel Hargreaves
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