Attracting Pallid Bats

Mark Kiser

The pallid bat (Antrozous pallidus) is recognized by its more than one inch-long ears and light yellowish fur. It lives in arid and semi-arid areas from Mexico and the southwestern United States northward to Washington and British Columbia (Figure 1), mostly at elevations below 5,000 feet. Unlike most insectivorous bats, it catches much of its prey on the ground, including crickets, grasshoppers, June beetles, leafhoppers, centipedes, and even scorpions.

Pallid bat colonies typically include only 12 to 100 individuals.
At night, they often roost under porches and overhangs, where they drop wings and other parts of large insects while eating. Day-roosting sites are usually in rock crevices, bridges, buildings, and occasionally in caves, mines, or hollow trees. The extent to which pallid bats are able to use bat houses, however, is not well understood. Do their needs differ from other bats, or are people just not reporting or identifying them?

During BCI’s first bat house survey in 1992, we received just one report of a bat house used by pallid bats. It was located near Prescott, Arizona and was installed on a masonry building from which the bats had been excluded. It was mounted under a deck facing southeast, was 12 inches (30.5 cm) wide and 18 inches (45.7 cm) tall, and included two roost crevices, each two inches (5.1 cm) wide. The bat house sheltered 30 to 50 pallid bats and was located 1/ 2 mile (800 m) from the nearest freshwater source in mountainous, desert habitat at about 5,000 feet (1.5 km) elevation.

Since the North American Bat House Research Project began in 1993, we have received just two other reports of pallid bats in bat houses. In 1996, Research Associate Doug Allen observed two occupied houses near San Diego, California. Both were single-chamber models with a roost crevice width of 1 1/ 2 (3.8 cm) inches from front to back. One house was mounted on a wooden pole on a patio and was used by six to eight pallid bats. This house faced north and received no direct sun. The other was installed on the south side of a wooden building where it received six to seven hours of daily sun. It sheltered up to 20 pallid and myotis bats. Allen found large numbers of moth wings and parts of scorpions on the ground underneath these houses, a tell-tale sign of pallid bat use. Both houses were occupied within two months of installation, but were used only as night roosts. Allen noted that the bats arrived in March and departed in
late May when ambient temperatures reached 105-110°F (41-43°C). He suspected they moved to higher elevations during the summer to escape the heat. The bats did not return to these houses in subsequent years.

In May 1999, BCI biologist Brian Keeley and Texas Parks and Wildlife biologist Annika Keeley discovered a colony of 75 to 100 pallid bats roosting in an extra-large bat house at Fort Leaton State Historical Park in Presidio County, Texas. The 8- by 8- by 8-foot (2.4- by 2.4- by 2.4-m) wooden structure has a beige stucco exterior and was built as an alternative roost for bats excluded from the historic buildings. With 84 crevices and a variety of crevice sizes to choose from, the pallid bats appeared to prefer crevices between 1 and 2 inches (2.5 and 5.1 cm).

Given the pallid bat’s size, and based on these reports, we suspect they prefer crevice sizes of 1 1/ 4 to 2 inches (3.2 to 5.1 cm) which are larger than most of our houses provide. We encourage Research Associates in western areas where pallid bats may occur, to conduct experiments with these crevice widths in mind. Because wasps can be a problem in houses with larger crevices, you may wish to add a restriction plate on the bottom of each house (use hinges to facilitate cleaning), leaving a 3/ 4-inch opening for bats to enter. Please let us know if you succeed in attracting these bats. Pictures would be greatly appreciated!