A bat house is a specialized wooden structure designed to provide a safe, warm roosting habitat for local bat populations. Proper installation is crucial for attracting bats, as they are highly sensitive to temperature and location. Success depends entirely on placement, which must optimize sun exposure and provide a clear flight path. Mounting the house on a tree requires careful planning to meet the bat’s thermal needs while ensuring the host tree’s long-term health.
Site Selection Criteria
The thermal requirements of bats necessitate positioning the house to maximize solar gain. A south-southeast orientation (approximately 140° azimuth) is optimal, ensuring the structure receives at least six to eight hours of direct sunlight. Morning sun is particularly beneficial for warming the roosting chambers. Bats, especially maternal colonies, need internal temperatures exceeding 85°F to conserve energy and promote the development of their young.
The height of the installation is important for both safety and accessibility. The bottom of the bat house should be mounted a minimum of ten feet above the ground to deter predators like raccoons and house cats. Raising the house to a height of 12 to 20 feet is better, as it provides bats with a greater vertical drop for safe flight emergence.
A clear, unobstructed flight corridor must be provided below and immediately in front of the house. Bats need a minimum of 20 feet of open space around the house to maneuver safely when entering and exiting the roost. Select a tree that is not heavily foliated or surrounded by dense branches that could block the house or provide perches for aerial predators.
Bat activity is significantly higher when the house is located within a quarter mile (about 1,500 feet) of a permanent water source, such as a pond or stream. This proximity offers convenient access to drinking water and concentrated insect populations, which are their primary food source.
Detailed Mounting Instructions
Attaching a bat house to a curved tree trunk requires a wooden mounting board or cleat to create a flat, stable surface. This cleat, typically made from weather-resistant lumber, should be secured to the tree first. The bat house is then attached to this cleat, rather than directly to the uneven surface of the tree bark.
Before installation, gather the necessary equipment, including a sturdy ladder, a power drill, and appropriate hardware. It is helpful to have the bat house assembled and the cleat attached to its back before hoisting the assembly up the tree. Once lifted into position, the house must be carefully leveled and firmly secured to the tree using long, heavy-duty lag screws or bolts.
The mounting process involves pre-drilling pilot holes through the cleat and into the tree trunk to prevent wood splitting and ease hardware insertion. Drive the lag screws in until the cleat is firmly held against the tree, but do not fully tighten them against the wood. This slight gap accounts for the tree’s natural expansion and movement over time. Use at least two mounting points—one near the top and one near the bottom of the cleat—to ensure stability against wind and weather.
Minimizing Harm to the Tree
The primary concern when mounting anything to a live tree is preventing girdling, which is the restriction of the tree’s vascular system that can lead to death. Materials like wire, chain, or rope must be avoided, as they will not stretch and will eventually cut into the expanding trunk. Secure the bat house using long, heavy-gauge galvanized or stainless steel lag bolts.
These long bolts are installed with a deliberate gap left between the back of the mounting board and the tree bark, often up to two or three inches. This allowance accommodates the tree’s radial growth, preventing the hardware from becoming embedded too quickly and allowing the tree to expand without restriction. Use stainless steel or galvanized hardware to prevent rust, which can stain the tree and potentially introduce harmful elements into the tree’s tissue.
The tree’s natural protective barrier, the bark, should be disturbed as little as possible. While a small amount of bark may be scraped away to allow the mounting cleat to sit flat, excessive removal is detrimental to the tree’s health. By selecting a large, mature tree and using the proper hardware with a growth gap, the bat house can be safely attached without compromising the tree’s health for decades.