INTRODUCTION. Bats are nocturnal, flying mammals which inhabit dark, secluded places. In western cultures, they have traditionally been associated with witchcraft, sorcery, haunted houses, cemeteries, and evil. For centuries, they have been the subject of fables, folklore, and myths. Unfortunately, many myths regarding their lives still exist and serve as a basis for unfounded fear. Bats are of medical concern because a very small percentage are infected with rabies, and old droppings may harbor the fungal organism that causes the lung disease histoplasmosis. There are over 980 species of bats worldwide with about 40 species occurring in the United States. However, none occur in the colder areas located beyond the limit of tree growth.
RECOGNITION. Depending on the species, adults about 2 3/16-7 1/2" in length from tip of nose to end of tail, wingspread about 6-15", and weight about 1/8-2 1/8 oz for United States species. Color tan to black. Head with very large ears. Fly on 2 wings consisting of a double membrane stretched across enlarged arm bones and elongated finger bones. Body covered with hair. With 2 pectorial teats.
Note that bat species are difficult to identify, even by the experts. If assistance is needed, contact the wildlife or zoology department of a local museum or university, fish and wildlife personnel, or the local health department.
REPRESENTATIVE SPECIES.
1. Big brown bat, Eptesicus fuscus (Beauvois); family Vespertilionidae. Adults about 4 1/8-5" long including tail, wingspread 12-14", and weight usually 2/5-3/5 oz ; color brown dorsally (light in deserts to dark in forests) and usually glossy, belly paler with hairs dark at base; and wings and interfemoral membrane (between leg and tail) black; no fur on wings or inter-femoral membrane; tragus (leaflike structure in ear) blunt; with 32 teeth and no reduced premolar behind canine; found throughout southern Canada and United States except for southern Florida.
2. Little brown bat, Myotis lucifugus (LeConte); family Vespertilionidae. Adults about 3
1/8-3 5/8" long including tail, wingspread 8 11/16-10 5/8", ears 1/2-5/8", and weight 1/8-1/2 oz; color various shades of glossy brown, hairs on back with long glossy tips, and belly buff; ears moderately long (bent forward reach nostril) with tragus (leaflike structure in ear) short and rounded; with 38 teeth; found from middle Alaska through southern Canada to throughout the United Sates except for Florida, Texas, and southern California.
3. Mexican/Brazilian free-tailed bat, Tadarida brasiliensis (Geoffroy), formerly T. mexicana; family Molossidae. Adults about 3 1/2-4 3/8" long including tail, wingspread 11 3/8-12 13/16", and weight 3/8-1/2 oz ; color usually chocolate brown, varies from dark brown to dark gray above with hairs whitish at base; fur velvety and short; ears separated at base; with 32 teeth; tail extending well beyond edge of tail membrane; found throughout southern United States, in the west extending north to southern Oregon and southern Nebraska, in the east extending north to northern Louisiana, Alabama, and South Carolina, and a few scattered further north.
BIOLOGY. Females preparing to give birth either found/establish nursery or maternity colonies in locations other than their overwintering site or remain in their all-season site. Little brown bats give birth to usually 1, but occasionally 2, young during May to July. The gestation period is about 50-80 days. Young are born naked, with the eyes opening in 2-3 days. Young are normally left hanging in the roost, but may be carried by the female. They are weaned at about 1 month. Big brown bats give birth to usually 2 (east of Rocky Mountains) or 1 (in Rockies and westward) young during April to July. Mexican free-tailed bats give birth to usually 1 young during late June which is weaned in July or August. Most bats live for an average of 4-10 years; ranges include big brown to 19 years, little brown to 20 years, and the Mexican free-tailed bat 13-38 years.
Bats have relatively poor vision and instead rely on echolocation (similar to sonar) to avoid objects and find prey. During flight the bat emits a series of supersonic sounds (about 30-60 squeaks/sec with a pitch of 30-100,000 cycles) through its nose or mouth which bounce off objects and are picked up by its ears.
Of general concern are the medical implications of bats and their droppings. First, only a very small percentage of bats are infected with rabies, but infected bats may not show any symptoms. Rabies can be transmitted when saliva or body tissue of an infected animal comes into contact with open wounds or mucous membranes, such as those of the eyes and nose, of another animal including humans; it is not necessary to be bitten by a rabid animal to become infected. The CDC (Centers for Disease Control) recommends pre-exposure rabies immunization for people in occupations that have an increased risk of rabies exposure, especially animal handlers. Immunization consists of 3 shots given over about a 30-day period, with about 20-25% of the vaccinated people reporting some kind of reaction (not life-threatening) to the shots. Pre-exposure immunization does not eliminate the need for post-exposure treatment, but it reduces the post-exposure regimen.
Second, accumulations of bat droppings in attics or soil create conditions suitable for the growth of Histoplasmosis capsulatum, a fungus which can cause the lung disease histoplasmosis. Infection occurs by breathing spores contained in dust found in the roost. In severe cases, histoplasmosis can be fatal.
HABITS. The 3 most common bats to enter structures are the 3 representative species given above, the big brown, the little brown, and the Mexican free-tailed bat. All 3 of these bats leave their roosts at dusk and return just before dawn. Usually their first stop is at a stream, pond, or lake for a drink of water and then feeding begins. Their habits can be summarized as follows;
1. Big brown bat females form nursery colonies in structures in the spring while males roost elsewhere; later in the summer the sexes roost together. They commonly roost in attics and church belfries and behind shutters and loose boards on buildings. They leave their roost about dusk in a slow, fluttering flight. These bats usually feed near the ground and feed on insects, primarily on beetles but also on wasps, ants, plant-hoppers, leaf-hoppers, flies, moths, etc. They are capable of flight up to 40 mph (24.8 km/hr) which is the fastest reported for any bat. Big brown bats are the most common bat to hibernate in structures in Canada. However, they typically disperse relatively short distances and hibernate singly or in small groups in hollow trees, rock crevices, drainage pipes, caves, mines, and buildings. In Canada, hibernation extends only from December to April.
2. Little brown bats form nursery colonies in structures in the spring. They feed on insects, especially flies and moths. They alternate feeding flights with rest periods during which they hang to digest their catch. Their flight is erratic with flight speed averaging 12.4 mph, but ranging up to 22 mph. In the north, most migrate south in the autumn with the migration covering up to 443 mi. From September/October through March/April they hibernate in irregular clusters, using mines and caves in the east. They have good homing instincts as illustrated by a return home in 3 weeks after being released 270 mi away.
3. Mexican free-tailed bats usually live in huge colonies where the young are raised. In the southeast and on the west coast they live in structures, but they live in caves from Texas to Arizona. Typically they fly at about 10-15 mph but can exceed 25 mph. Sometimes they may go up to 50-150 miles distant to their feeding grounds. They feed on insects, especially moths, but also ants, beetles, leafhoppers, etc. captured in the inter-femoral membrane. They eat up to 1/3 their body weight each night. Those in the southeast and on the west coast hibernate but do not migrate. Most of those in Texas to Arizona migrate to Mexico for the winter, sometimes traveling over 800 mi (1,288 km). They leave in late October and return in March.
