Selecting a Quality Bat House

By Merlin Tuttle
2/15/19

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
U.S.A.

 

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

 

(alphabetically)

BatBnB

Bat Conservation & Management

Habitat for Bats

 

We invite suggestions and feedback on your experiences.

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Young Conservationist Makes a Difference

Young Conservationist Makes a Difference
12/6/18

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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Collaboration to Improve Housing for Bats

9/20/18

Harrison (standing) and Christopher showing off their new BatBnB houses.

For the past 18 months Merlin has been assisting Harrison Broadhurst and Christopher Rannefors in creating a line of designer bat houses, attractive to both home owners and bats. Their curving architecture isn’t, just pleasing to the eye. At least theoretically, it may increase the area available for roosting, since most bats appear to prefer to line up with faces exposed to the outside air, not to another’s posterior, quite understandable!

The new houses are constructed of kiln-dried, sustainably sourced, three-quarter-inch western red cedar, with each piece dovetailed and caulked, thus minimizing leakage. Roosting chambers are extra tall (20-26 inches) and vented to ensure thermal gradients preferred by bats. All landing and roosting surfaces provide one-eighth-inch-deep cross cuts at half-inch intervals, ensuring maximum footholds for young bats. By avoiding plywood, the possibility of early deterioration and potential off-gassing are finally eliminated. Furthermore, treatment with Thompson’s WaterSeal Semi Transparent Stain & Sealer will additionally protect against warping.  BatBnBs come with complete instructions and are easy to mount.

We’re proud to be a part of Harrison and Chris’ efforts on behalf of bats and a safer environment. They’ve been featured in dozens of leading publications and have even appeared on several television shows. You can learn more about them and obtain your own BatBnB by visiting their online shop. By using the code MERLIN when ordering you will be given a 10% discount, and the company will donate to MTBC an additional 5% of all orders using this code. Feel free to share this discount and BatBnB’s website with friends and let us know about your progress. By purchasing a BatBnB, you can reduce the threat of harmful pesticides in your neighborhood and help MTBC educate the world about these invaluable neighbors.

 

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New Bat Housing Partnership

New Bat Housing Partnership
10/22/16

Merlin spent most of yesterday meeting with Steve Barlow of Wildlife Integration, sharing knowledge from their bat house experiences. Steve was a partner in Merlin’s original North American Bat House Research Project, who continued his innovative experiments long after the project ended. He has shown extraordinary creativity in developing and testing new designs, including a new “Community Size Bat House” that has been highly successful in attracting thousands of bats per dwelling. Following an enthusiastic exchange of ideas, they decided to partner in developing and promoting dwellings for bats.

 

Steve Barlow & Merlin Tuttle

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Monitoring Impacts of WNS

Monitoring Impacts of White-Nose Syndrome (WNS): Decline and Stabilization in a Little Brown Bat Nursery Colony,

A Case History from New York

By Merlin D. Tuttle
9/25/16

 

A New York nursery colony of little brown myotis (Myotis lucifugus) offers a window of opportunity for monitoring the impact and hoped for recovery of this recently devastated species. The colony occupies seven four-chamber, nursery-style bat houses provided by Lew and Dorothy Barnes. The houses were mounted on two sides of their barn near Lake Erie in western New York in the spring of 1995. By July 16, 1997 they had attracted 1,075 little brown myotis. Often aided by professional biologists, regular emergence counts were made between 1997 and 2013, providing potentially invaluable baseline data on WNS-induced population impacts.

(more…)

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World’s First Artificial Bat Cave

World’s First Artificial Bat Cave Provides Model for Future
By Merlin Tuttle
8/14/2016

 

The chiroptorium covers 3,000 square feet (279 square meters) and offers about 8,000 square feet (743 square meters) of likely roosting surface. A structure of welded-together rebar, coated in heavy plastic, was then sprayed with a foot of gunite to form a permanent shell.

Modern bats face a serious housing shortage. Millions of homeless bats have died when their caves were destroyed or converted to exclusive human use, not to mention when old-growth forests were logged. Often, the single most important action we can take to restore bats today is to provide alternative homes.

We know from long experience that desperate bats often readily occupy human-made structures, from abandoned mines and railroad tunnels to old buildings. Though building backyard bat houses is an excellent way to help, sometimes it is very much in our mutual interest to provide long-lasting structures that can accommodate large numbers, not only for pest control, but also for the pure entertainment large colonies can provide.

Construction crew working in entrance passage. Vertical braces were removed once the gunite hardened.

When J. David Bamberger was first introduced to an evening emergence of the millions of Brazilian free-tailed bats (Tadarida brasiliensis) at Bracken Cave in the Texas Hill Country, he was awestruck. He fell in love with this wonder of nature and soon began asking if it would be possible to attract a miniature Bracken colony to his ranch. Undaunted by an absence of caves, he asked me about the feasibility of “building” a cave.  Would bats come? (more…)

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Formosan golden bats of Taiwan

Mr. Chang and mascot of the Formosan Golden Bat's Home

Mr. Chang and mascot of the Formosan Golden Bats’ Home

Following 30 hours of travel, we spent our first day recuperating in Taipei, got up early the next morning for a 2.5-hour drive to the Formosan Golden Bat’s Home on the campus of the Sheng-Zheng Elementary School, where we met our host, 43-year-old Heng-Chia Chang. As a teacher, he had noticed beautiful little golden bats (Myotis formosus flavus) roosting in school yard tree foliage. (more…)

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Finding bat roosts in Trinidad

Our digital and social media coordinator, Teresa Nichta, is learning firsthand the challenges of bat photography, whether in the studio or in the wild. This is her experience in her words.

I already knew I would love the rain forest; it was so massive yet I felt right at home.

Documenting where bats live was a major objective of this trip, and that was just what we did!  Of course, I’d seen Merlin’s photos and learned about what we were looking for but seeing bats at home in the forest in person was even more enthralling than I had imagined. Bats are nearly everywhere but they’re seldom seen because they hide so well. (more…)

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Photographing North America’s Rarest Bat

An endangered Florida bonneted bat, America’s rarest bat, once thought to be extinct.

America’s rarest bat, the endangered Florida bonneted bat (Eumops floridanus), was once relatively common. It often lived in tile roofs of Coral Gables and Miami, and its loud, low-frequency echolocation calls made it easy to detect. The species declined sharply in the 1950’s and early 1960’s, and by the late 1970’s extinction was feared. Then in 1978 woodcutters found a male and seven females in a woodpecker cavity. Soon several more were found living in a backyard bat house.

(more…)

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