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February 2011 cover image A Wish for a Fish

Skill Builder: Not Just Yard Art for the Addams Family

Installing a bat house near your home gives these night-flyers a place to stop over.

By Kathryn Hunter

In suburban yards, purple martin and bluebird houses are more common than garden gnomes. Custom-made habitats have allowed these two species to prosper, though the number of cavity-nesting songbirds is generally on the decline. The bat — several species of which are endangered — could greatly benefit from similar care, and is a creature that offers its own benefits to human landlords as daytime tenants.

An individual bat can eat 500 to 1,000 mosquitoes an hour. And though mosquitoes aren’t every bat species’ preferred diet, bats also eat other pests, including moths, cockroaches, beetles, stink bugs, grasshoppers, scorpions and centipedes. Research has also shown that some insects avoid areas where bats live.

Bats don’t bore holes or otherwise create their roosting habitat. Rather, they are migratory opportunists, known to roost under bridges and in attics, barns and even the occasional patio umbrella. Bats do, however, prefer specific dimensions. Through more than a decade of research and continued feedback from Bat Conservation International members and citizen scientists, BCI has developed a basic schema that appeals to bats’ tastes. Plans for bat houses can be found in The Bat House Builder’s Handbook, and the plan for a single-chambered bat house is free on BCI’s website.

Building BCI’s single-chambered bat house is simple and can be an enjoyable family project. A large piece of plywood makes up the backing of the house, and is grooved horizontally — these grooves serve as a “landing pad” on the bottom-most edge of the house and, inside, are what the bats cling to. (A plastic screen can be substituted.) Two smaller pieces of plywood, attached to furring strips that separate them about 1 inch from the backing, cover the front, with a small gap left between them serving as a vent to prevent the interior from getting too hot. A roof is added to the top, but, unlike birdhouses, a bat house has no “floor.” All gaps on the sides and top of the house are caulked well to prevent drafts. The finished product is very tall and wide, and though the cavity the bats are meant to live in seems impossibly narrow, this tiny space can host more than 50 bats at a time. BCI’s community bat house design can hold up to 30,000.

Much of a bat house’s success depends on maintaining a temperature of 80 to 100 degrees inside. For this reason, it is recommended that the house be placed where it will receive six or more hours of sun a day and that all exterior surfaces of the house be painted using either water-based stain or paint of the shade suggested by BCI for the region. In areas where temperatures in July average less than 85 degrees Fahrenheit, dark colors should be used, and light colors should be used where temperatures exceed 100 degrees.

Installation of the bat house is also very important. Ideally, a bat house should be located within at least a quarter-mile of a body of water, 20 feet away from power lines or trees and 12 feet or more (from the bottom of the bat house) above ground on the side of a building or on a pole. Bats do not tend to use houses mounted on trees or metal siding or those placed in brightly lit areas. Proximity to an established colony increases the chance that bats will use the house, and the best time of year for installation is early March.

While some individual bats are simply passing through, others establish sparsely populated “bachelor pads” or large maternity colonies. Seven species in Texas, most commonly the Mexican free-tailed bat (Tadarida brasiliensis) and the Evening bat (Nycticeius humeralis), have been known to inhabit bat houses. Once a house is occupied for a season, bats tend to return every year.

“If bats don’t use the house right away, give it a couple of seasons, then try moving or repainting it,” says Rebecca Patterson, programs administrator for BCI. Also, before a new season starts, remove any wasps or mud dauber nests that might be present.

If woodworking isn’t your hobby but bats are, ready-made houses can be purchased from BCI at 800-538-BATS or www.batcon.org. Some models include a “bat cam” that allows you to monitor activity within the box. Otherwise, you can watch your bats emerge from their swanky new accommodations at dusk.

 

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