Maintaining proper roost temperature is probably the single most important factor for bat house success. Temperatures inside a bat house should be warm, and as stable as possible for mother bats to raise their young (ideally 80° F to 100° F in summer). Some species, like the big brown bat, can tolerate temperatures in excess of 100° F. Bachelor bats are less picky, and may use houses with cooler temperatures. Wooden or masonry structures are the best mounting sites, especially in colder climates, as temperatures are more stable than houses attached to poles or trees.
Bat house temperatures are influenced directly by:
• The exterior color (dark, medium, or light paints or stains)
• Orientation (east, southeast, or south facing are generally good bets for single houses in most climates)
• The amount of sun exposure
• How well the house is caulked and vented
• The mounting substrate and construction materials used
You may have to experiment to get the right placement and temperature range. You can always use a thermometer taped to a pole to see if temperatures are suitable inside the bat house. Check temperature from top, bottom, front and back. Where possible, installing multiple houses provide a range of options. Bats may move from one house to another throughout the year to find more favorable micro-climates, or to deter predators.
Where To Put Your Bat House
Pick installation sites with great care to avoid having to move a bat house once it becomes occupied.
Most bat houses have open bottoms, so guano will not accumulate inside, but on the ground underneath. Avoid placing bat houses directly above windows, doors, decks, or walkways, as bat urine may stain some finishes. To avoid guano collecting on a wall, widen the landing area below by using spacers or a large backboard between the bat house and the wall.
A potted plant, shallow tray, or saucer can be placed underneath to collect guano for use as fertilizer in flower beds or gardens. DO NOT use a bucket or deep container to catch droppings, as baby bats that fall will become trapped inside (unless 1/4″ or smaller mesh covers the entire top of the container). Some bat species are able to retrieve their pups from the ground.
Once you have attracted bats, as a “bat house landlord” it is your responsibility to maintain the houses in good condition to keep bats coming back year after year:
• Bat houses should be monitored at least once a month (preferably more) to detect potential problems such as predators, overheating, wood deterioration, etc.
• Wasp and mud dauber nests should be cleaned out each winter after bats and wasps have departed.
• New caulk and paint or stain may be required after three to five years to guard against leaks and drafts.
Any repairs or cleaning should be performed when bats are not present.