Why bat houses may fail

Why Bat Houses Fail

Few bat house manufacturers promote their products with photographs of bats actually using their boxes. While it is tricky to get great shots of bats in or emerging from bat houses, the problem more likely lies with bats simply refusing to use them.
Bat houses found in most shopping mall nature stores, mail order catalogs, nationwide hardware stores, and birdhouse websites are from antiquated plans. They are usually designed to be quick and cheap to build. For several years now we have been teaching the bat house building segment at the annual BCI Bat Conservation and Management Pennsylvania Workshop. Participants are always surprised to learn all the details that go into a successful bat house. We teach them bat houses usually fail because of one of three reasons:

poor design
poor construction
poor placement

Common bat house design and construction problems

Bad bat house designs are flawed from the start. They are often too small with crevices that are too wide. Sometimes critical details are omitted, such as landing plates and vents. These houses usually cannot compete with a modern design, even after being upgraded by a creative hobbyist. Bad construction is different and can sometimes be solved with paint, caulk, extra screws, and extra roughening. Common problems encountered in bad designs are:

A single chamber box. Bats simply prefer larger structures which offer a wider range of stable temperatures. A tightly built single chamber bat house may be good "starter" box that would be great for giveaways to the general public.
Factory smooth interior crevices. All interior wood must be roughened for bats to readily cling to. Some commercial boxes staple screening to the inside of the box which may eventually fall off as condensation and urine rusts the staples. A "bat house" seen for sale at a major hardware store had only one groove on the "landing plate"; this simply doesn't provide a rough enough surface for bats.
Unprotected roof. Roofs without shingles may last only a few seasons, once the roof is compromised the box will be incapable of retaining heat and fall into disuse.
Nailed together with unsealed seams. This type of box will warp and separate at the seams allowing unwanted ventilation and disuse.
Unpainted, unprotected exterior. Some manufacturers insist on leaving bat boxes unpainted. While in certain regions the natural wood color may be a suitable color, there is no good reason for the structure to go unprotected. While cedar is rot resistant, it will warp and separate at the seams just as any other wood material does.
Bad design. Bat research has proceeded at a very fast rate, thanks to improved communication among different hobbyists and biologists across the country. For example, a tall open-bottomed bat house is now preferred over smaller closed bottom designs which tend to attract more parasites.
Old plans. Bat house plans can be found in a variety of places, which is good. Unfortunately, many of these posters, books, and flyers are out of date and contain antiquated plans. Frighteningly, this information is still distributed by many reputable sources. A stack of utterly horrid plans obtained from a state wildlife agency were seen distributed at a wildlife program just a few years ago.
"Recycled" material. Some people construct well designed bat houses with lumber salvaged from demolished structures in effort to cut costs. As some pesticides can leave active residues for years, approach used lumber with caution.
Unrealistic claims. For example, a seven chamber bat house was once observed with nearly 600 bats inside. However, we rate our 7 chamber bat house at a capacity of 300 bats. This is because 600 bats in this size bat house is overcrowded and unhealthy.

One of many experimental bat boxes built in Pennsylvania. This design is mildly successful but can get too hot internally due to the short overall height of the box. The bottom door must be kept closed to keep stray light from driving off bats. This same door allows guano and parasites to build up. Tall, open bottom BCM boxes give bats a temperature gradient and are self-cleaning.

Common placement mistakes:

The greatest bat house in the world will never be used unless it is placed properly. In cool climates it is best to avoid shady locations. Often this limits the mounting options to strategically placed posts or sunny chimneys. Bad placement includes the following:

A bat house that is in a shady location. It needs a minimum of seven hours of morning sunlight.
A bat house mounted on a tree. Rarely will the box ever receive enough direct sunlight in cool climates.
Bat house placed on a structure, directly under the eves. The eves may shade the bat house.
Placed too far from permanent water. Dry, arid locations are less desirable, though bats will drink from swimming pools.
Located over bright surfaces which reflect light into the bat house. Shiny flashing or pans placed to collect guano may deter use at certain times of the season.
Located near burn barrels or air vents where smoke or strong wind will disturb bats. Beware of air conditioner units which may not be active when installation occurs.
Erected where the box is prone to vandalism. Shaking the bat house to watch them fly out during the daytime will cause your bats to abandon the bat house.
Placed in brightly lighted areas. Avoid mounting where dusk-to-dawn lights shine directly onto the box.
Erected directly along roads where bats are vulnerable to automobile traffic during their dawn return.
No maintenance. Some mounting solutions turn a quick yearly inspection into a difficult and even dangerous ordeal. Bat houses do require minor wasp and seam inspection, otherwise bats will begin to abandon the box. Be alert for a hornet invasion as well; bats will immediately abandon a bat house until these aggressive insects are removed.

This bat house at the left is large, which is good. Bats seem to like larger structures over tiny "bird house sized" boxes being offered today in hardware, nature, garden, and science stores. Though large, this box with it's 1''-2'' interior baffle spacing (too wide), lack of landing plate, and shady placement on a tree all contribute to it's failure. This box can be upgraded to a degree with the addition of a landing plate, a fresh round of sealant, and a sunny location. Fixing the all-important interior crevices would require total disassembly, time better spent creating a new box with a new design.

Now that you are an expert on bat houses, please see our bat house shoot out. Make sure any box you consider for purchase or build as a kit is certified by the North American Bat House Research Project, part of Bat Conservation International!
Be sure your plans are up to date! For all sorts of bird and mammal box plans get Woodcrafting for Wildlife, third edition available on this website today!

Why Bat Houses Fail
Few bat house manufacturers promote their products with photographs of bats actually using their boxes. While it is tricky to get great shots of bats in or emerging from bat houses, the problem more likely lies with bats simply refusing to use them. Bat houses found in most shopping mall nature stores, mail order catalogs, nationwide hardware stores, and birdhouse websites are from antiquated plans. They are usually designed to be quick and cheap to build. For several years now we have been teaching the bat house building segment at the annual BCI Bat Conservation and Management Pennsylvania Workshop. Participants are always surprised to learn all the details that go into a successful bat house. We teach them bat houses usually fail because of one of three reasons: poor design poor construction poor placement Common bat house design and construction problems Bad bat house designs are flawed from the start. They are often too small with crevices that are too wide. Sometimes critical details are omitted, such as landing plates and vents. These houses usually cannot compete with a modern design, even after being upgraded by a creative hobbyist. Bad construction is different and can sometimes be solved with paint, caulk, extra screws, and extra roughening. Common problems encountered in bad designs are: A single chamber box. Bats simply prefer larger structures which offer a wider range of stable temperatures. A tightly built single chamber bat house may be good "starter" box that would be great for giveaways to the general public. Factory smooth interior crevices. All interior wood must be roughened for bats to readily cling to. Some commercial boxes staple screening to the inside of the box which may eventually fall off as condensation and urine rusts the staples. A "bat house" seen for sale at a major hardware store had only one groove on the "landing plate"; this simply doesn't provide a rough enough surface for bats. Unprotected roof. Roofs without shingles may last only a few seasons, once the roof is compromised the box will be incapable of retaining heat and fall into disuse. Nailed together with unsealed seams. This type of box will warp and separate at the seams allowing unwanted ventilation and disuse. Unpainted, unprotected exterior. Some manufacturers insist on leaving bat boxes unpainted. While in certain regions the natural wood color may be a suitable color, there is no good reason for the structure to go unprotected. While cedar is rot resistant, it will warp and separate at the seams just as any other wood material does. Bad design. Bat research has proceeded at a very fast rate, thanks to improved communication among different hobbyists and biologists across the country. For example, a tall open-bottomed bat house is now preferred over smaller closed bottom designs which tend to attract more parasites. Old plans. Bat house plans can be found in a variety of places, which is good. Unfortunately, many of these posters, books, and flyers are out of date and contain antiquated plans. Frighteningly, this information is still distributed by many reputable sources. A stack of utterly horrid plans obtained from a state wildlife agency were seen distributed at a wildlife program just a few years ago. "Recycled" material. Some people construct well designed bat houses with lumber salvaged from demolished structures in effort to cut costs. As some pesticides can leave active residues for years, approach used lumber with caution. Unrealistic claims. For example, a seven chamber bat house was once observed with nearly 600 bats inside. However, we rate our 7 chamber bat house at a capacity of 300 bats. This is because 600 bats in this size bat house is overcrowded and unhealthy. One of many experimental bat boxes built in Pennsylvania. This design is mildly successful but can get too hot internally due to the short overall height of the box. The bottom door must be kept closed to keep stray light from driving off bats. This same door allows guano and parasites to build up. Tall, open bottom BCM boxes give bats a temperature gradient and are self-cleaning. Common placement mistakes: The greatest bat house in the world will never be used unless it is placed properly. In cool climates it is best to avoid shady locations. Often this limits the mounting options to strategically placed posts or sunny chimneys. Bad placement includes the following: A bat house that is in a shady location. It needs a minimum of seven hours of morning sunlight. A bat house mounted on a tree. Rarely will the box ever receive enough direct sunlight in cool climates. Bat house placed on a structure, directly under the eves. The eves may shade the bat house. Placed too far from permanent water. Dry, arid locations are less desirable, though bats will drink from swimming pools. Located over bright surfaces which reflect light into the bat house. Shiny flashing or pans placed to collect guano may deter use at certain times of the season. Located near burn barrels or air vents where smoke or strong wind will disturb bats. Beware of air conditioner units which may not be active when installation occurs. Erected where the box is prone to vandalism. Shaking the bat house to watch them fly out during the daytime will cause your bats to abandon the bat house. Placed in brightly lighted areas. Avoid mounting where dusk-to-dawn lights shine directly onto the box. Erected directly along roads where bats are vulnerable to automobile traffic during their dawn return. No maintenance. Some mounting solutions turn a quick yearly inspection into a difficult and even dangerous ordeal. Bat houses do require minor wasp and seam inspection, otherwise bats will begin to abandon the box. Be alert for a hornet invasion as well; bats will immediately abandon a bat house until these aggressive insects are removed.

			This bat house at the left is large, which is good. Bats seem to like larger structures over tiny "bird house sized" boxes being offered today in hardware, nature, garden, and science stores. Though large, this box with it's 1''-2'' interior baffle spacing (too wide), lack of landing plate, and shady placement on a tree all contribute to it's failure. This box can be upgraded to a degree with the addition of a landing plate, a fresh round of sealant, and a sunny location. Fixing the all-important interior crevices would require total disassembly, time better spent creating a new box with a new design.
			Now that you are an expert on bat houses, please see our bat house shoot out. Make sure any box you consider for purchase or build as a kit is certified by the North American Bat House Research Project, part of Bat Conservation International! Be sure your plans are up to date! For all sorts of bird and mammal box plans get Woodcrafting for Wildlife, third edition available on this website today!