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).
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.
Bat House Builders’ Handbook: Download