BAT HOUSES

Some people are interested in encouraging bat populations by installing artificial roosting sites or bat boxes. Bat houses aren't likely to discourage bats from roosting in nearby buildings, and there is no clear evidence that their installation will significantly reduce garden insect problems. If you chose to put up a bat house, make sure it is in an area that has minimal disturbance from people and animals. Sometimes sick bats fall out of the roost where children and household pets easily can pick them up.

Bat houses and bat-house designs are widely available commercially. Follow the guidelines below when constructing and installing a bat house:

• Use rough-sided wood on the interior of the house. Horizontally groove the interior surface for toe holds.
• Roosting chambers should be 1/2 to 1 inch wide; chambers larger than 1 inch invite wasps.
• Caulk outside seams to limit airflow.
• Use roofing felt (tar paper) or dark roof shingles on top and 6 inches down the sides to increase inside temperatures; a 90°F inside temperature is ideal.
• Install bat houses at least 10 feet above ground with an eastern or northern exposure. Bats prefer houses that get morning sun and afternoon shade.
• Protect the house from prevailing winds, if possible, and provide an unobstructed approach for flying bats.

Bat houses attached to the sides of buildings tend to have the greatest success, but be careful, since bat droppings will accumulate below. Bat houses on poles in open areas sometimes work, but bats rarely occupy houses placed in trees. Installing bat houses before March improves the chance of occupancy. It is not unusual for bat houses to remain unoccupied for a year or more. Bats prefer houses that are within 1/4 mile of water with enough room to drink on the wing. More information on bat boxes is available in the UC ANR publication Songbird, Bat and Owl Boxes.

This excerpt is from ipm.ucanr.edu.