Selecting a Quality Bat House

Merlin Tuttle
February 15, 2019
Bat Houses, Resources: Bat Houses

Since Merlin first introduced bat houses to North America in 1982, one of the most frequently asked questions has been, “Where can I purchase a good bat house?” The next question that always follows is, “How do I know bats will come?”

Over the decades, we’ve learned much about bat preferences and how to attract them. Today, high-quality bat houses, when properly located, are achieving up to 80% success in attracting bats. However, finding reliable vendors whose bat houses meet the needs of bats has been the biggest challenge. Many purchasers have become discouraged by the failure of cheap, poorly constructed bat houses or even good ones sold with inadequate instructions. It’s crucial to ensure that the bat house you purchase is made with proper materials, design, and dimensions, and is installed in the correct location. By doing so, you can provide a safe and comfortable roosting space for bats while enjoying the benefits of these incredible animals in your yard. We hope to help you on your journey to selecting a quality bat house.

Introducing Our Newest Resource…

T he Bat House Guide combines the wisdom of America’s most experienced bat house pioneers and innovative builders worldwide. It is the definitive resource for bat house information. Coauthors, Dr. Tuttle, and Danielle Cordani share their findings from surveys of thousands of houses, explaining conflicting results and opinions, and suggesting areas for further experimentation.

Guided by dazzling photographs, readers will not only discover bat houses from all over the world but learn how to construct and mount their very own. The book also includes builder’s plans, key criteria for success, novel options, suggestions for experimentation, and frequently asked questions.

Characteristics of a Quality Bat House

Wherever you live, several species, including most temperate-zone bats, will likely prefer roosting crevices 3/4” wide. Big brown bats (Eptesicus fuscus) are found throughout most of North America and will readily accept chamber widths of 7/8″ to 1″. A few species may prefer 1″ to 1-1/2” crevices such as the endangered Florida bonneted bat (Eumops floridanus) that lives only in central and southern Florida, and the Pallid bat (Antrozous pallidus) that occurs in arid and semi-arid areas of the West, from southern Canada through much of Mexico. However, roosting crevices greater than 1″ wide should be tested only where larger species are being targeted.
Taller houses, at least 20″ tall, provide the best thermal range and are ideal for single-chamber houses exposed to direct sun. Shorter houses should be used only where the risk of overheating is minimal.
Tight-fit construction and caulking of all external seams reduce leakage and warping that can lead to early deterioration and abandonment.
The greatest resistance to weathering and warping can be provided by outer shells of aluminum or UV-resistant plastic. However, houses made of solid wood, at least 3/4″ thick, have proven highly successful without painting. Houses of thinner wood that remain unsealed or painted often become warped and uninhabitable within 2 to 3 years.
All exterior parts of wooden houses should be at least 1/2” thick. Any plywood used should be exterior grade.
All interior surfaces and landing areas must be roughened, enabling bats to gain secure footing. Horizontal grooves 1/16″ deep at 1/4″ to 3/4″ intervals are ideal. However, grooves should not be cut more than 1/32″ deep for plywood surfaces to avoid early deterioration. Hand-roughened or rough-cut surfaces also work well.
All bat houses should have a roughened landing area extending at least 4” below the roosting partitions. Additionally extending the sides, back, and front approximately 4” below the roosting partitions provides a recessed landing area that protects against owl attacks during entry.

What Size and Color to Choose

With the improvement in bat house quality and knowledge of preferred mounting locations, the exact size and number of chambers have become less important. As long as bat needs are met, a wide variety of bat houses can be successful.

Single-chamber houses are often more vulnerable to temperature change compared to double- or triple-chamber houses. However, they can be successful when exposed to appropriate amounts of sun or shade, or when mounted on buildings that stabilize temperature. Taller houses offer a range of temperatures and are more likely to meet bat needs, regardless of the number of chambers.

Multiple bat houses of different colors or sun exposure often work well when placed in close proximity to one another. An early bat house study showed that people who provided two or more houses were twice as successful. Before purchasing a large bat house designed to shelter hundreds or thousands of bats, we recommend starting with multiple single-chamber houses of varied color or sun exposure to offer a variety of temperatures for bats to roost. By watching bat behavior on especially hot or cool days, you can easily evaluate what they need in your particular location.

In colder regions, bats have a strong preference for dark brown or black houses and they should be position to maximize solar heating. In hot climates, medium brown houses can still be attractive if they’re well-vented and have a metal roof to protect from the mid-day sun. Unless protected by a roof, lighter-brown (or equivalent) and well-vented houses are preferred.

Where to Mount Your Bat House

Bats thrive in mixed habitats near freshwater sources like lakes or rivers. They also tend to form successful colonies in buildings where they’ve attempted to roost. While not all bat species prefer o roost in crevices, those that do are typically the most abundant, including at least ten species that occupy bat houses in North America. On the other hand, areas surrounded by large expanses of buildings or single-crop agriculture tend to be the least attractive to bats.

It’s important to place bat houses in sunny areas, except in the hottest climates. The outer walls of buildings are the most suitable mounting sites for small bat houses, especially in arid areas or cold climates. Buildings act as heat sinks, which help to stabilize the temperature inside the houses. A North American study found that bat houses mounted on trees are the 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 are also more vulnerable to predators. To avoid areas of potentially high predation, it’s best to keep bat houses at least 20 feet from the nearest tree limbs or perches. In warm climates, pole-mounted houses may require snake guards similar to those used to protect purple martins.

When to Expect Occupants

In areas of high demand, even poorly designed bat houses can attract occupants within a few days. On average, it takes two to six months for bats to occupy a bat house, and in some cases, it may take years for successful occupancy. Areas where bats have previously used bat houses are likely to experience early success. Extraordinarily successful houses, particularly those that are larger in size, may take two to three years or more to attract occupants. It is worth noting that the largest bat houses often take the longest to attract their first occupants, but with time and patience, large-scale constructions can eventually attract thousands or even hundreds of thousands of bats.

It is important to be patient and avoid the temptation to add bat guano or other attractants, as there is no evidence to suggest that this will expedite the process. Some bat houses may attract occupants immediately, but in areas where bat houses have not been used before, it often takes between 12 to 18 months for bats to occupy the space.

Learn more about how MTBC is improving bat houses in America.

MTBC-Approved Bat House Vendors

The following retailers (listed alphabetically) meet most of our criteria for bat house access and longevity, To be considered for our certification program, please use our Instructions for Applicants.