Bat houses are specially constructed shelters designed to provide artificial roosting habitat for wild bat populations. They serve as a conservation tool, particularly for female bats needing warm, secure locations to raise their young in maternity colonies. The success of a bat house depends almost entirely on its placement and the microclimate it creates. Factors like sun exposure, mounting height, and surrounding landscape directly influence the internal temperature and the bats’ sense of safety. Correct installation is the most important action to maximize the chances of attracting a colony.
Optimizing Sun Exposure and Temperature
Temperature regulation is the most significant factor determining bat house occupancy, especially for maternity colonies which require a consistently warm environment. Female bats need the internal temperature of the roost to be between 80°F and 100°F (27° to 38°C) for the rapid development of their pups. If the house is too cold, the pups may not survive or the colony may abandon the roost entirely.
The house must receive substantial daily solar exposure, ideally six to ten hours of direct sunlight. In the Northern Hemisphere, orienting the bat house South or Southeast (around 140° azimuth) maximizes sun exposure. This captures the morning and early afternoon sun, heating the house to the preferred range.
The exterior color must be chosen based on the local climate to fine-tune the internal temperature. In cooler regions (July high below 85°F), paint the house black or a dark shade to maximize heat absorption. In hot climates (July highs exceed 100°F), a lighter color like tan or gray prevents overheating. Moderate climates should use medium shades of brown or gray, using only water-based exterior paint or stain.
Ideal Mounting Height and Support Structures
The elevation of the bat house relates to both temperature and security, requiring a minimum height of 12 feet. Placing the house between 15 and 20 feet off the ground is better, as this height protects bats from ground predators and clears surrounding obstacles. This elevation allows bats a clear drop and unimpeded flight path upon exiting the roost at dusk.
Mounting the house on a metal pole is often the most successful method because it allows for full solar exposure and defends against climbing predators like raccoons and snakes. Attaching a bat house directly to the side of a building, especially brick or stucco, is a good alternative. The building material absorbs and radiates heat, stabilizing the internal temperature overnight.
Mounting a bat house on a tree is the least effective option. Trees provide too much shade, interfering with solar heating, and their branches offer easy perches for aerial predators like owls. Furthermore, trees provide a direct route for climbing predators to access the roost, lowering the chances of long-term occupancy.
Landscape Features and Flight Paths
The immediate environment must accommodate the bats’ flight needs, requiring a clear approach for safe entry and exit. An open area extending 20 to 30 feet in front of and below the house must be free of wires, branches, or obstructions. Bats will not use a roost if they must navigate a cluttered space, as this makes them vulnerable to predators.
An ideal location is situated near a water source, such as a pond, lake, or stream, within 1/4 mile (400 meters) of the roost. Bats need water for drinking, and proximity ensures access to wet habitats where insect prey breed. The surrounding area should also contain open fields and forest edges, providing diverse foraging grounds.
While the house should be placed near foraging areas, it must not be positioned directly under a dense tree canopy or shaded by large branches. Keeping the house 20 to 30 feet away from the nearest tree line prevents aerial predators from perching close by. This distance still offers a nearby element for the bats to follow for quick cover.
Common Installation Errors
Several common mistakes can prevent occupancy, even if the solar orientation is correct. One frequent error is using pressure-treated lumber, as the chemicals can be toxic to bats. All wood used must be untreated, and only a water-based exterior paint or stain should be applied.
Many houses fail because the installer neglects to properly caulk and seal all external joints and seams before painting. Unsealed joints allow cold air to infiltrate, making it impossible to maintain the high temperatures needed for a maternity colony. Another error is purchasing a house that is too small; single-chamber designs offer less thermal stability and are less successful than multi-chamber houses.
The timing of the installation matters; a bat house must be put up well before the bats return from migration in the spring. Installing the house in the late winter or early spring allows the wood time to off-gas any paint or sealant odors and weather slightly, making it more appealing. A house installed too late may be overlooked by migrating bats that have already chosen their summer roost.