Family: Molossidae, Free-tailed Bats view all from this family
Description The largest bat in North America. Body sparsely furred; fur dark brown; hairs white at base. Enormous ears, joined at base, protrude over forehead. L 5 1/2-7 1/4" (140-185 mm); T 1 3/8-3 1/8" (35-80 mm); HF average 5/8" (17 mm); FA 2 7/8-3 1/4" (72-82 mm); E 1-1 5/8" (25-40 mm); Wt average 2 1/4 oz (65 g).
Warning 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 and report it to animal-control officers. If you are bitten by a possibly rabid animal, you must immediately consult a doctor for a series of injections; there is no cure once symptoms emerge.
Similar Species Underwood's Mastiff Bat is smaller, with smaller ears.
Breeding Mates in early spring. Gestation is estimated at 80-90 days. 1 young born usually June-July.
Habitat Rocky cliff and canyon areas. Roosts in crevices, also in buildings.
Range Southern California, extreme s Nevada, s Arizona, extreme sw New Mexico, and Big Bend area of Texas.
Discussion By day, these bats form small colonies, usually with fewer than 100 members. Because of their large size and long wings, they require considerable space to launch themselves into flight, so roosting sites are usually situated to permit a free downward fall for at least 10 feet (3 m). They roost in crevices, choosing long vertical slits at least 2 inches (50 mm) wide, from which they climb rapidly to a narrower spot and wedge themselves in. Roosts are sometimes alternated throughout the year. As night approaches, loud squeaks may be heard near roost entrances. During flight, cries are frequent and can be heard more than 1,000 feet (300 m) away. Foraging high and at great distances from roosting sites, the bats feed primarily on moths, which constitute 80 percent of their diet, but also eat ground-living crickets and long-horned grasshoppers. The Western Mastiff often crawls on all fours with its tail sticking straight up and perhaps serving as a tactile organ. The way its large ears cover its head has earned this creature the nickname "Bonnet Bat."
Sign: Crevices used for day roosts often marked by yellowish urine stains on rocks below and by large-size droppings.
