Bats and Mines in the California Desert
Abandoned mines house significant colonies of bats, many of which include threatened and endangered species. Bats are important and valued members of the environment; they can eat up to half their weight in insects each night and are instrumental in pollination and seed dispersal. Because many natural bat habitats have been disturbed or destroyed, bats have found new homes in abandoned mines. Bat Conservation International, the BLM, the Forest Service, FWS, and National Park Service have partnered to help protect vulnerable bat species in abandoned mines.
The California Leaf-nosed Bat is the only bat in North America, north of Mexico, with large ears and leaf-like projection on the nose. It roosts by day, usually fairly close to the entrance of a mine tunnel, in small groups of up to 100 bats, which do not touch each other. This species cannot crawl on thumbs and toes like most bats, but instead often dangles by one leg from a mine tunnel's ceiling, which it can cross in a swinging stride, using its hind legs alternately.
After dark, this species drops from its perch into flight. Leaf-nosed Bats eat various insects, including some flightless forms, such as crickets and some beetles, which they probably detect as they hover, swooping down to seize them from the ground. After feeding for about an hour, they retreat to their night roosts in a sheltered area. They do not hibernate. Male California Leaf-nosed Bats occupy bachelors' quarters in July and August, soon thereafter joining the females for the mating season.
Townsend's Big Eared Bats are found in Western Canada, the Western United States to Southern Mexico, with a few isolated populations in the Eastern United States.
These bats hibernate in caves or mines where the temperature is 54 degrees F or cooler, but normally above freezing favoring well ventilated areas. If the temperature near the entrance becomes too cold they may move deeper into the cave to gain stability. Maternity colonies are usually located in warmer parts of caves and during the maternity period males appear to be solitary. Although no long distance migrations are known, like many bats they return to the same roost each year. Western populations of this bat are stable however eastern populations are endangered.
Pallid bats are fairly common at lower elevations throughout the Southwest Deserts. Its favored habitat is the rocky outcrop regions where the dominant vegetation consists of scattered desert scrub such as mesquite and cat's claw. Summer daytime roosts are most common in rock crevices, buildings, mines, and caves. Colonies are small, usually from a dozen to 100 individuals.
These bats normal daytime roosting site is where they can retreat out of sight and wedge themselves into tight crevices. They are intolerant of disturbance and may abandon a roost when disturbed, not to return for years. Pallid bats make several different sounds which apparently have different functions. The intimidation note is a loud insect-like buzz that is uttered when a bat is frightened, angered, or annoyed. The squabble note consists of several high-pitched, dry, rasping, thin double notes. It appears to be a sign of irritation, uttered by individuals which are being crowded by others. The directive call consists of one to five rapidly repeated notes. This call is usually given as soon as the bat emerges in the evening.
Pallid Bat photo courtesy of Dr. Pat Brown
Pallid bats have one of the most unique feeding habits of any North American bat. Little, if any, of their food is captured in the air. Some of their favorite food includes scorpions, crickets, grasshoppers, and spiders. People have reported they have seen pallid bats landing on the ground and chasing crickets.
Bats are susceptible to rabies, a serious viral disease that results in death if untreated. Rabid bats rarely attack humans or other animals, but bats found lying on the ground may be rabid. Never touch or pick up any bat. Stay away from any animal that seems to be acting strangely. If you are bitten by a possibly rabid animal, you must immediately consult a doctor.