Getting Involved

Research

North American Bat House Research Project (1993-2004)

A Decade of Bat House Discovery

America’s first known bat houses were built near San Antonio, Texas, in 1902. Hardly anyone noticed, and the idea of artificial bat roosts languished for the next eight decades. Then came the 1980s, and Bat Conservation International became the pivotal promoter of bat houses as an inexpensive way to help bats while cashing in on their voracious appetites for bothersome insects.

Bat houses began popping up in backyards, farmlands, and orchards around the U.S. and Canada, but their effectiveness was still hotly debated as recently as the early 1990s. Few systematic observations existed on the sizes, shapes, colors, building materials, or locations bats might prefer.

In the spring of 1993, BCI launched the North American Bat House Research Project, a long-term volunteer effort to quantify roosting preferences and fine-tune artificial roosts to better meet the needs of bats.

“The North American Bat House Research Project has revolutionized our ability to help bats in need of homes, thanks to the 7,000 Research Associate volunteers and colleagues who, over more than a decade, have shared their findings from varied climates and habitats across the continent. Today, at least 16 of 46 U.S. and Canadian bat species are using bat houses and other artificial roosts that shelter tens of thousands of bats, with 100,000 in just one extra-large structure.

Our efforts have mostly focused on species that prefer to roost in ¾-inch (19 millimeter) crevices, and, with the help of our Research Associates, we developed a basic bat house design that has proven acceptable for the majority of America’s most widespread species. Such houses, which do not require species-specific knowledge, enable countless novice bat fanciers, farmers and wildlife managers to install successful bat houses.

By sharing and analyzing the results of numerous tests involving crevice-dwelling species in wide-ranging habitats and climates, we have clearly documented key requirements. As research progressed, we periodically added new, more-refined reporting categories, which limits the number of years available for cross-comparison. We are, however, able to make consistent comparisons for 1,553 bat houses reported from 1998 to 2001.”

That excerpt is from Vol. 12, No. 1, Spring 2004, The Bat House Researcher, which was published twice in most years between 1994 and 2004. This was the final newsletter as the official project ended, and it summarizes the most important results from the experimentation across the U.S. and Canada. We have again posted every newsletter from this project so that you can read for yourself all about the experiments that individuals carried out on their own properties and the resulting knowledge that was gained. Though they are not recently written, the information they contain is still as relevant as it was from 1994 to 2004, and answers many common questions that are still asked by the public.

So, read, learn and enjoy--it is still a great idea to create more homes for bats—maybe more now than it ever has been!

Newsletter Archive

View the scanned copies of the The Bat House Researcher newsletter below. (Arranged by year and season)

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Pictured here is a bat house testing site.
Copyright Brian Keeley, Bat Conservation International



Tips and Guidelines

Attracting Bats

Two pole mounted bat houses Credit: Mark Kiser

Bats have to find new roosts on their own. Existing evidence strongly suggests that lures or attractants (including bat guano) will NOT attract bats to a bat house. Bats investigate new roosting opportunities while foraging at night, and they are expert at detecting crevices, cracks, nooks and crannies that offer shelter from the elements and predators. Bat houses installed on buildings or poles are easier for bats to locate, have greater occupancy rates and are occupied two and a half times faster than those mounted on trees.

Unlike domestic animals, bats are wild and free-ranging. It is usually illegal to buy or sell them, and permits to capture and possess bats are generally limited to researchers, zoos, wildlife rehabilitators and educational organizations. Catching and relocating bats to new areas is, in any case, highly unlikely to succeed. Bats have strong homing instincts, and once released into a bat house, will attempt to return to their former home area. Consequently, placing bats in a bat house is usually futile and is not recommended. If a bat house remains unoccupied after two full years, consider repositioning of modifying the house.

The odds of attracting bats are very good for well-designed, well-built bat houses mounted according to recommendations developed by the Bat House Project during 12 years of bat house research by BCI and its volunteer Research Associates across the U.S., Canada and the Caribbean. This project found:

  • Bats inhabited an average of 60 percent of all reported bat houses (both good and bad houses and installations) in BCI's 1999 to 2001 annual surveys.
  • Occupancy in rural areas was 61 percent, compared to 50 percent for urban and suburban areas.
  • 90 percent of occupied bat houses were used within two years (with 50 percent occupancy in the first year). The rest needed three to five years for bats to move in.
  • Tall designs like the multi-chamber (nursery) and rocket-style houses performed best in our surveys. For example, 80 percent of 123 houses with chambers at least 25 inches tall were occupied in 2000.

 

Temperatures

Maintaining proper roost temperatures is probably the single most important factor for a successful bat house. Interior temperatures should be warm and as stable as possible (ideally 80º F to 100º F in summer) for mother bats to raise their young. Some species, such as the big brown bat, prefer temperatures below 95º F, while others, such as the little brown bat, tolerate temperatures in excess of 100º F. Bachelor bats are less picky and may use houses with cooler temperatures. The sides of wooden or masonry structure are the best mounting sites, especially in colder climates, because temperatures are more stable than for houses attached to poles.

Bat house temperatures are influenced directly by the exterior color, compass orientation (east-, southeast-, or south-facing are generally good bets for single houses in most climates), the amount of sun exposure, how well the house is caulked and vented, and the mounting and construction materials. You may have to experiment to get the right placement and temperature range. You can always use a thermometer taped to a pole to see if temperatures are suitable inside the bat house (check the chambers high and low, and front and back).

 

 

Bat house near water
Bat house do well near water Credit: Mark and Selena Kiser

Installation Sites

Pick installation sites with care so you don’t have to move it after it is occupied. Most bat houses have open bottoms, which keeps guano from accumulating inside. Guano will, however, end up on the ground underneath, so avoid placing bat houses directly above windows, doors, decks or walkways. Bat urine may stain some finishes. Two- or four-inch spacers between a bat house and the wall, a large backboard or a longer landing area below a bat house may reduce guano deposits on the wall. A potted plant or a shallow tray or plant saucer can be placed underneath a bat house to collect bat guano for use as fertilizer in flower beds or gardens. Do not use a bucket or deep container (unless 1⁄4-inch or smaller mesh covers the entire top of the container), as any baby bats that fall from the bat house could become trapped inside. For more installation advice visit our Install page. 

 

Maintaining you bat house

Once you have attracted bats, you must maintain the bat houses to keep bats coming back year after year. Wasp and mud dauber nests should be cleaned out each winter after bats and wasps have departed. New caulk and paint or stain may be required after three to five years to guard against leaks and drafts. Bat houses should be monitored at least once a month (preferably more often) to detect potential problems such as predators, overheating, wood deterioration, etc. Any repairs or cleaning should be performed when bats are not present.

 

Getting rid of wasps

As the bats’ landlord, it is your duty to make sure the bat house is in good shape and is habitable. This means doing routine maintenance on the house and taking care of unwanted guests. Some of the most common non-bat visitors to bat houses are wasps. Wasps can be a problem before bats fully occupy a house. Use of 3/4-inch roosting spaces reduces the risk of wasps. If nests accumulate, they should be removed in late winter or early spring before either wasps or bats return. Open-bottom houses greatly reduce problems with birds, mice, squirrels or parasites, and guano does not accumulate inside. 

Buy

Many commercial bat houses are not suitable for bats because of inadequate design or construction, or they lack proper instructions concerning painting, placement, sun exposure and mounting. BCI's Bat Approved Certification Program has worked since 1998 to improve the quality of bat houses and to provide some guidance for anyone interested in purchasing a bat house.

Manufacturers who wish to earn the Bat Approved certification must submit a finished bat house for evaluation. Only those houses that meet all criteria are certified. All certifications are permanent as long as the design remains the same. For more information see the Certification Program Guidelines.

Here is a list of vendors that BCI has certified for bat houses intended to serve as artificial roosting habitat for most bat species found in the United States and Canada.

Arizona

Big Bat Box

Phoenix, AZ
Tel: 970-305-6430
3-Chamber Nursery Cedar Bat Houses
Free Shipping Anywhere in the USA

California

AML Enterprises, Inc.

3349 Mount McKinley Drive
San Jose, CA 95127-4808
Tel: 408-887-5331
4-chamber bat house
Single-chamber bat house

Napa Valley PSI

P.O. Box 600
651 Trabajo Lane
Napa, CA 94559-0600
Tel: 707-255-0177
Single-chamber bat house

Colorado

NUWTIQUES

10805 Hat Creek Pl.
Black Forest, CO 80908
Tel: 719-494-8391
Luxurious Two-Chamber Bat Home

Pikes Peak Market

90 Freeman Drive
Florissant, CO 80816
Tel: 719.246.9145
Three-Chamber Bat House

Connecticut

Richard Kurtz

220 East St. N.
Suffield, CT 06078
Tel: (860)668-6449
Three chamber nursery house

Florida

Fly By Night, Inc.

P.O. Box 562
Osteen, FL 32764
Tel: (407)414-2142
Nursery Bat House
(3 chambers)

Nature's Friend

1470 Ft. Smith Blvd.
Deltona, FL 32725
Tel: (386)860-5021
2-Chamber Nursery House
3-Chamber Nursery House

Georgia

Habitat for Bats

2258 Highway 16 East
Jackson, GA 30233
Tel: (770)500-2851
1 Chamber "Series E-1"
2 Chamber "Series E-2"
3 Chamber "Series E-3"
4 Chamber "Series E-4"
7 Chamber "Series E-7"
Single Chamber Bat House DIY Kit

Pebble Hill Grove

9047 Moultrie Hwy.
Quitman, GA 31642
Tel: (229)775-3347
3-Chamber Nursery House*
5-Chamber Nursery House*
5-Chamber "Triple-Wide" Nursery House

Wildlife Integration LLC

3514 Gloucester Ct
Martinez, GA 30907
Tel: 803-480-5608
Model #WI244 Community Bat House
Model #WI444 Community Bat House

Massachusetts

Bat Bungalows

Chicopee, MA 01020
Tel: 413.330.1798
Small Single-chamber bat house
Large Single-chamber bat house
Three-chamber bat house
Four-chamber bat house

Michigan

BatsBirdsYard, L.L.C.

Hartland, MI
Tel: 810-602-4707
Single Cell Deluxe Bat House
Double Cell Deluxe Club House
Triple Cell Deluxe Nursery
Four Cell Deluxe Apartment Complex
Five Cell Deluxe Condo Unit
LIFETIME WARRANTY


HCV Bat Houses

8135 Stonehedge Dr.
Gregory, MI 48137
Single-Chamber Bat House

Heart & Eagle Company

Grand Rapids, MI
Tel: 616-456-5991
Cathedral Bat House (double chamber)
Cathedral Bat House (triple chamber)
(All green products, made from re-purposed, century-old barn siding).

Polly Products

12 N. Charlotte St.
Mulliken, MI 48861
Tel: 877-609-2243
(chat available 8 am-5pm M-F, EST)

3 Chamber Bat House
Made of recycled #2 HDPE for hygiene and durability
‘Donate a Bat House to Your Park’ program

Montana

Cabin Fever Woodworking

2730 Kid Curry Dr.
Bozeman, MT 59718
Tel: (406)587-9243
Large Bat House
(2 chambers)

New Hampshire

P&S Country Crafts

1441 Peaked Hill Road
Bristol, NH 03222
Tel: (603) 744-2265
2-chamber bat house

New Mexico

Framewerkgallery.com

1 Clauss Pl
Tijeras, NM 87059
Tel: 505.264.3001
Single Chamber Bat House

New York

Wendy and Frank Ludwig

75 Champlin Ave.
Bellport, NY 11713
Tel: (631)974-6243
2-Chamber Bat House

North Carolina

Tuckaway Treasures

P.O. Box 322
Tuckasegee, NC 28783
Tel: (828)293-9314
Large Single-Chamber Bat House

North Dakota

homes4bats

Jerry Kallod
2420 South University Drive
Fargo, ND 58103
Tel: 701.730.6818
2-Chamber Bat House
Almost Maintenance-Free
No wood products used
Weather resistant materials -- Light-weight --Durable--Thermal insulating

Ontario

Canadian Bat Houses

419 E. Christina St.
Thunder Bay, ON P7C 4P3
Tel: (807)628-7625
Tall 2-chamber nursery house
Standard 2-chamber nursery house

Houses are covered with water proof rubber membrane exterior.

Oregon

Bat Bunker

93759 Troy Lane
Coos Bay, OR 97420
Tel: 541.269.7351
Large Roto Molded Bat House with Removable Four-Chamber Cedar Baffle System --

Suitable for Maternity Colony

No maintenance required!

NUWTIQUES

28020 Crossley Ln./
Eugene, OR 97402
Tel: 719-494-8391
Luxurious Two-Chamber Bat Home

Pennsylvania

Bat Conservation and Management

220 Old Stone House Road
Carlisle, PA 17013
Tel: (717)241-ABAT (2228)
Standard Bat Box (7 chambers)
Nine-Chamber Bat House
Six-Chamber Bat Bunker Plus Bat House
Five-Chamber Nursery House
Four-Chamber Premium Bat House (sold at batgoods.com)
Three-Chamber Bat House (sold at batgoods.com)

Enterprises of Garden Gate

6473 Ruch Road
Bethlehem, PA 18017
Tel: 610-837-1114
2-Chamber Bat House

Texas

Austin Batworks

1712 E. Riverside Dr.
#353
Austin, TX 78741
Tel: 512.861.8303
Small Single-chamber bat house
Large Single-chamber bat house
Three-chamber bat house
Four-chamber bat house

Lone Star Woodcraft

San Antonio, TX
Tel: (210)885-0811
Triple-celled bat house

West Virginia

AllStar Ecology, LLC

1582 Meadowdale Road
Fairmont, WV 26554
Tel: 304 816-3490
Two-Chambered Rocket Box
Four-Chambered Nursery Box

Wisconsin

Barn in the Sticks

3553 Davis Lane
Blanchardville, WI 53516
Tel: 608.214.9511
"Dad's Black Bat House"

Three-Chamber Bat House

Mary Dussling

Madison Area, WI
Tel: (608) 513-9497
4-chamber nursery house

Wisconsin Humane Society Wildlife Rehabilitation Center

4500 W. Wisconsin Avenue
Milwaukee, WI 53208
Tel: 414-431-6204
See the single-chamber bat houses available for purchase on our website.

All proceeds go to the Wisconsin Humane Society, a non-profit organization. Thank you for your support!

Visit www.wihumane.org/wildlife to learn more about the live-saving work that we do!

Install

Mexican free-tailed bats returning to a bat house
Credit: Mark Kiser

Once your bat house is constructed or purchased, it’s important to choose an area for installation that has the best chance of attracting bats. How and where you mount your new bat roost depends on the style and size of bat house, average temperatures in your area in July, and certain other physical limitations. Bat houses can be mounted on wooden posts, steel poles, pivot poles, or on the sides of buildings, but should not be mounted on trees for three reasons:  

  1. They receive less sun among the branches
  2. Bat tenants are more vulnerable to predators
  3. Obstructions in the form of branches and surrounding vegetation make it more difficult for bats to drop into flight.

Bats find houses mounted on poles or buildings in less than half the time it takes them to find tree-mounted roosts. Houses mounted under the eaves on wood or stone buildings, but still exposed to the sun, tend to be better protected from rain and predators and have been especially successful. Bat houses should be mounted in an area that gets 6-8 hours of direct sunlight (facing either East or South).

Bat houses on a barn
Bat houses on a barn Credit: Mylea Bayless

Buildings offer good mounting sites almost everywhere, but they are essential in very cool or dry climates. In dry areas, where day-to-night temperatures may vary by more than 28°F, buffering from nighttime extremes is needed. Buildings are the right choice if you are installing only one, single-chamber bat house. Unless two are installed back-to-back, pole-mounted singled-chamber roosts don’t seem to offer enough options for bats to move about in response to temperature fluctuations. Pole mounted bat houses can however be very successful. Nursery colonies of up to 1,100 bats have been recorded to take up residence in pairs of nursery houses mounted on poles back-to- back, 3⁄4 inch apart and covered by a tin roof.

Where climates are moderate to hot with average to high humidity, it is best to test pairs of houses mounted back-to-back on poles –a light one facing north and a moderate to dark one facing south. Houses of different colors can also be tested side by side on buildings, with both houses facing the same direction, in any climate. By observing roost choices of the first occupants, bat preferences can be determined and met by varying the color or sun exposure for subsequent houses.

To the extent possible, locate all houses 20 to 30 feet from tree branches or other obstacles and 12 to 20 feet above ground (or above the tallest vegetation beneath the bat house). Those located nearest an area’s largest water source are typically the most successful, as are those in or adjacent to the most diverse or natural vegetation. The best locations are along streams, rivers, lakes or forests because these are natural bat flyways.

 

Resources


Further Reading From BATS Magazine








Build

Little brown myotis using a bat house. Credit: Mark and Selena Kiser

Building your own bat house is a great way to get involved in bat conservation. Bat species worldwide are experiencing habitat loss, and building an artificial roost can give our bat friends a safe and comfortable place to live. Here on our website we have designs for three different types of roosts - single chamber, four-chamber, and rocket boxes. Volunteers with BCI’s Bat House Research Project (1993-2004) conducted research on hundreds of bat houses and other artificial roosts, and the designs linked on this page incorporate the most successful features identified in those tests. These bat houses are designed to accommodate 14 different species of North American bats.

The correct bat house for you depends on available tools and lumber, your skill as a carpenter, your budget and your expectations. You can, of course, modify your bat house to adjust for location-specific factors, such as climate and the preferences of local species.

The most successful bat houses have roost chambers at least 20 inches tall and at least 14 inches wide. Taller and wider houses are even better. Rocket boxes, a pole-mounted design with continuous, 360°chambers, should be at least 3 feet tall (see Figure 6 on page 14 of the Bat House Builders Handbook). All houses should have 3- to 6-inch landing areas extending below the entrances or recessed partitions with landing space inside.

The number of roosting chambers is not critical, but in general, the more chambers the better. Single-chambered houses should be mounted on wooden or masonry buildings, which helps to buffer temperature fluctuations. Houses with at least three chambers are more likely to provide appropriate ranges of temperature and better accommodate the larger numbers of bats typical of nursery colonies. Two single-chamber houses can be mounted back-to-back on two poles to create a three-chamber bat house.

Bellingen Flyout
Jadyn, 10 years old, proved herself a very
capable woodworker (with a little help from her
grandpa). Credit: Woodworkers Guild of America

 

Bat Conservation International worked with the Woodworkers Guild of America to develop some bat house building instructions and videos! Click here to check out this great resource! 

 

 

 

 

 

Construction

Building a bat house
Building a bat house Credit: Janet Tyburec

For single-chamber and nursery houses (Figures 3 to 5), 1⁄2-inch (or thicker) exterior plywood is ideal for fronts, backs and roofs, while 1- or 2-inch-thick boards are best for the sides. One-inch (3⁄4-inch nominal size) cedar or poplar lumber is recommended for rocket boxes. Roofs for any roost type can be built of 3⁄4-inch exterior plywood to increase longevity. Cover roofs with shingles or metal for extra protection. Plywood should have a minimum of four plies for durability. Using 3⁄8-inch plywood for roosting partitions reduces weight and allows more roosting space for a given house size.

Pressure-treated wood contains chemicals that may be toxic to bats and should be used only if sealed by painting. Alternative materials, such as plastic or fiber-cement board, may last longer than wood and require less maintenance.

Coated deck screws or other exterior-grade screws should be used instead of nails to assemble houses. Staples used to attach plastic mesh should not protrude from the backs of panels and must be exterior grade or galvanized to prevent corrosion. All seams must be caulked, especially around the roof, prior to painting. Latex caulk is paintable and is the easiest to use.

Color Recommendations

The temperature of your bat house greatly affects whether or not bats will take up residency. Since the color you paint the roost affects the amount of light it absorbs, you can influence the box’s internal temperature. Consult the map below to figure out what color will work best for your location.

Bat House Color Recommendations
Bat House Color Recommendations and Average Daily High Temperatures in July

        1. Blue areas: less than 85˚ F. – Black or dark shade of paint.     

        2. Green areas: 85˚-95˚ F. – Dark or medium shade of paint.       

        3. Yellow areas: 95˚-100˚ F. – Medium or light shade of paint.

        4. Light pink areas: 100˚ F or greater. – White or light shade of paint.

 

Resources

For more information about constructing, painting, installing and maintaining your bat house, please see:

 

Further Reading From BATS Magazine

More Articles...

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