Farmscaping for Birds and Bats

Birds and bats are important insect predators, particularly during the spring when they are raising young. Their activities complement each other. Birds are generally active during the day and feed on caterpillars and other insects, while bats feed during dusk and into the night on mosquitoes, moths, and other nocturnal insects.

Birds and bats are both amenable to living in artificial shelters—free-standing or attached to a building. This could be a slightly modified structural component of a building, such as nest shelves along eaves for barn swallows (10) or a spaced board attached to a beam for bat habitat. Bats, frequently found in man-made structures, prefer places that are warm, dry, and protected from disturbance (11).

Both birds and bats will benefit from having a small pond or body of water on the property or nearby. Bats require a watering area ideally 10 feet long, as they drink “on the fly.” Birds will be content with birdbath-size and larger water bodies.

One difficulty in farmscaping for birds is that some birds’ diets change from insects to seeds (or to fruit) after they have finished rearing their young. The following table lists some bird species that may be considered for farmscaping efforts.

Bats not only eat insects that are a nuisance to humans (a small brown bat can devour up to 600 mosquitoes in an hour), but can provide significant agricultural pest control services. In one season, a typical colony of about 150 big brown bats in the Midwest eats 50,000 leafhoppers, 38,000 cucumber beetles, 16,000 June bugs, and 19,000 stink bugs (11)—not to mention thousands of moths such as adult cornborers, earworms, and cutworms.

Bat Housing

The easiest way to construct bat housing is to simply add a sheet of plywood to a barn or house wall with ¾” spacers between the sheet and wall. Placing the long axis of the plywood vertically will allow for greater temperature variation in the bat space. (See Useful Contacts for contacts who know about bat habitat and housing.)

Other construction considerations include (11):

• Use exterior-grade plywood with exterior-grade staples and bolts.
• Minimum bat house dimensions are 32” tall, 14” wide, with 3–6” landing pad below the opening.
• Provide 1–4 roosting chambers, spaced at ¾”. Landing pad and roosting chamber should be roughened or have a durable textured surface for the bats to grasp—no sharp points to tear bat wings!
• Front and side venting should be appropriate for local climate.
• All seams should be caulked to avoid leaks.
• Treating bat houses with diluted bat guano or allowing some weathering of a new bat house may help attract new “renters”.

Considerations when locating a bat house (11):

• Any place that already has bats is best, particularly agricultural areas (vs. urban areas) due to insect abundance and habitat variety.
• Place the bat house near water—within a quarter mile is ideal.
• Place it near some sort of protective cover like a grove of trees—don’t place houses in a grove of trees, but 20–25 ft. away due to predator concerns, and at least 10 ft. above the ground.
• Don’t place bat houses near barn owl boxes—the barn owl is a bat predator. Place the two types of boxes a fair distance from each other facing in opposite directions.
• Do not mount bat houses on metal buildings (too hot for bats) or in locations exposed to bright lights.
• In California, bat houses in barns and on the north and west sides of buildings have had the greatest rate of occupancy. This may not be true for locations in other parts of the country.
• Paint the exterior with three coats of outdoor paint. Available observations suggest that the color should be black where average high temperatures in July are 80–85° F, dark colors (such as dark brown or gray) where they are 85–95° F, medium or light colors where they are 95–100° F, and white where they exceed 100° F. Much depends upon amount of sun exposure; adjust to darker colors for less sun. (14)

For further information about bats and bat houses, contact:

Bat Conservation International
PO Box 162603 Austin, TX 78716
(512) 327-9721
http://www.batcon.org/

or contact,
Rachel Freeman Long
Yolo County Farm Advisor
UC Cooperative Extension
(530) 666-8143