Brazilian Free-Tailed Bat

Brazilian Free-Tailed Bat (Tadarida brasiliensis, also known as the Mexican Free-Tailed Bat.

Brazilian Free-Tailed Bat
Image Copyright (c) Merlin D. Tuttle

Description: Body length about 3.4-4.3″, with a 12-14″ wingspan. The fur is uniformly dark brown or dark grey. The tail extends beyond the tail membrane between hind feet. Long narrow wings provide for fast flight.

Range: Migratory. Found from central North America to northern South America.

Habitat: Form large colonies in caves, buildings, under roof tiles and under bridges.

Diet: Forages mainly on moths. A farmer’s friend eating moths whose larva eats crops. Feed on migratory moths at very high altitude, up to 10,000 feet. Also eats flying ants, weevils, stink-bugs and ground beetles.

Behavior: Emerge at sunset in columns. Young left in large group. Each mother gives birth to one pup which she finds and nurses among the many young. Able to fly at about 5 weeks. Lifespan about 15 years. Predators include Red-tailed Hawk and other birds of prey, as well as cats and dogs which locate roosts and wait for emergence.

Risks: Colonies once numbering in the millions have been dramatically reduces in size due to human disturbance and habitat destruction of caves as well as problems with pesticide poisoning and deliberate eradication attempts.

Pallid Bat

Pallid Bat (Antrozous pallidus).

Pallid Bat
Image Copyright (c) Merlin D. Tuttle

Description: Body length about 3.6 to 5.3″, with a 15-16″ wingspan. Beige fur above, almost white below. Broad wings. Has very big pale ears and good vision. Musk gland.

Range: Across much of west North American from British Colombia to west Texas, Baja and Central Mexico.

Habitat: Grasslands and deserts. Roosts in rock crevices, caves, mine shafts, under bridges, in buildings and tree hollows. Some hibernate; many remain active all year in low to mid-elevations.

Diet: Crickets, scorpions, beetles, grasshoppers, various other insects. Feed primarily on the ground as well as gleaning from leaves. With its large ears, it can hear the footsteps of insects on the ground, and then swoops down to grab them. Immune to scorpion venom.

Behavior: Emerges about an hour after sunset. Eat, then go to night roosts to digest food, then will hunt again before dawn. Roosts in small colonies of about 12 to 100 bats. Forms nursery colonies, bears one or two pups each year, which nurse 6-8 weeks. Able to fly at about 6 weeks. Lifespan in wild unknown, have lived 9 years in captivity.

Risks: Maternal colonies and hibernating bats sensitive to disturbance. Loss or modification of foraging habitat, esp. urban development. Species of Special Concern in California

Bat Terminology

Mexican Free-Tailed BatDefinition of terms when describing bats:

Calcara cartilaginous structure protruding from the ankle supports the back edge of the interfemoral membrane. The interfemoral membrane acts as a rudder and also reduces oscillations of the body through each wing-beat cycle

Forearm: longest bone in arm, with hook-like thumb at one end.

Keel: flap of skin on edge of tail which is a distinctive projection of the calcar. See photo of keel and calcar at: University of Michigan Museum of Zoology

Total lengthmeasured from nose tip to tail tip.

Premolars: are the teeth with points, just behind the canine. Molars are further back and are relatively flat.

Tragus: a projection surrounded by external ear flap, often stiffened with cartilage. Ours is a little blunt one, in front, center of ear, forming front of entrance to ear canal.


Big Brown Bat

Big Brown Bat (Eptesicus fuscus)

Big Brown Bat
Image Copyright (c) Merlin D. Tuttle

Description: Body length about 3.4-5.4″, with a 13-16″ wingspan. Uniformly brown fur.

Range: Range: Very common bat in North America.

Habitat: Usually roost in old buildings, barns, behind shutters or in hollow trees. Often fly around city lights feeding on insects attracted to the light. Hibernate in cool, dry areas.

Diet: Beetles, ants, flies, leafhoppers, mayflies. Consume many agricultural pests. Often eat the equivalent of their body weight in insects each night.

Behavior: Emerge about 20 minutes after sunset. Often give birth to twins. Fly at 3-4 weeks of age. Hibernation can use up to 1/3 of body weight. Predators include hawks and Great Horned Owls. Lifespan about 19 years.

Risks: Roost disturbance during hibernation can cause starvation.

California Myotis

California Myotis (Myotis californicus)

California Myotis
Image Copyright (c) Merlin D. Tuttle

Description: Body length about 2.8-3.7″, with an 11-13″ wingspan. Light tan to black dull fur. Keeled calcar, Forearm less that 35 mm. One of the smallest of our bats.

Range: West coast of North America from Alaska to southern Mexico. Low elevations, not in interior mountains. Common in riparian area. Many may not hibernate.

Habitat: Day roosts in crevices, under bark, rock outcroppings, hollow trees, behind signs or in caves and mines. Hunts mostly over the water and along the forest edge.

Diet: moths, mosquitoes, flies and beetles.

Behavior: Peak activity about 1 hour after sunset. Special storage of fat on back may be converted to heat during cold periods. Mothers give birth to one pup. Young fly at 4 weeks. Females roost alone or form small maternity colonies. Lifespan 15 years or more.


Yuma Myotis

Yuma Myotis (Myotis yumanensis)

Yuma Myotis
Image Copyright (c) Merlin D. Tuttle

Description: Body length about 3.0-3.5″, with a 9-10″ wingspan. Light brown to dark brown back and paler under side. Large feet and short ears. Wings and ears are dark brown. Very similar to the Little Brown Bat

Range: From British Colombia, across western US, Baja and to southern Mexico. Hibernate in winter.

Habitat: Emerges early in evening. Found in buildings, cliff crevices, trees, caves, mines and under bridges.

Diet: Emerges just after sunset. Usually feeds near water, filling up in about 15 minutes. Consumes aquatic emergent insects, including mayflies, caddis flies, midges, small beetles, flies, termites, and small moths.

Behavior: Flies low. Forms colonies of up to 5,000 bats. Mother bat gives birth to one pup.

Risk: Maternal colonies do not tolerate disturbance by people: they fail or are abandoned with subsequent decline in population. Since it lives in human dwellings, it is vulnerable to destructive pest control activities.

Western Red Bat

Western Red Bat (Lasiurus blossevillii)

Western Red Bat
Image Copyright (c) Merlin D. Tuttle

Description: Body length about 4″, with an 11-13″ wingspan. Orange-brown to yellow-brown fur with a fully furred tail membrane. Long pointed wings. Short rounded ears.

Range: Throughout California, some in Washington, Utah and Arizona, to Central America, Argentina and Chile. Migratory from coast to valley.

Habitat: Edge habitats of forest, rivers, fields and urban areas. Roost alone in leaves of trees. Roost in leaf litter in the winter.

Diet: Peak activity one to two hours after sunset. Eats moths, beetles, flying ants and other insects.

Behavior: Fast, strong fliers at treetop to a few feet above the ground. Hangs by one foot with head tucked in furry tail membrane. Gives birth to up to 4 pups. If the mother has to move with her pups, she may become grounded due to weight of pups and unable to return with pups a roost. Predators: Scrub Jays, falcons, hawks, owls, opossums and domestic cats.

Risks: Loss of riparian zones, pesticide use in orchards and controlled burns of leaf litter.

Hoary Bat

Hoary Bat (Lasiurus cinereus)

Hoary Bat
Image Copyright (c) Merlin D. Tuttle

Description: Body length about 5.1-5.9″, with a 13-16″ wingspan. Blackish-brown or tan fur with frosted appearance. Tail membrane fully furred. Chattering and hissing sounds audible to humans. Ears rounded and glossy black. Golden color around face.

Range: Widespread distribution throughout North America and Hawaii as well as Brazil to Argentina and Chile. Migrates in flocks to warmer climates for winter.

Habitat: Roosts in foliage of trees near ends of branches. Blends with the bark of trees. Highly associated with forested habitats but can be found in suburbs with old, large trees.

Diet: Emerges late in evening, two to five hours after sunset. Hunts at treetop level, fields, over streams and around outdoor lights. Eats moths, true bugs, mosquitoes, dragonflies, and other insects.

Behavior: Solitary bat. Furry tail used as a blanket. One to four pups (two is norm). Pups fly at 4-5 weeks. Predators: Jays, kestrels, hawks, owls and snakes.

Risks: Loss of habitat due to timber harvest. In suburban settings, quantity of jays poses a major threat.

Little Brown Myotis

Little Brown Myotis (Myotis lucifugus)

Little Brown Myotis
Image Copyright (c) Merlin D. Tuttle

Description: Body length about 2.4-4.0″, with a 9-11″ wingspan. Glossy pale tan to dark brown, evenly colored fur. Long hairs on toes. Small, black pointed ears with blunt tragus.

Range: Woodland, forest bat. May be the most abundant bat in North America. Ranges from Alaska to Monterey, then down Sierras, across Canada and US. Typically absent from hot, dry lowlands.

Habitat: Roosts in large groups in caves, rock crevices, hot attics, buildings and bat houses. Also use dead and dying trees near water. Migrates to hibernation caves and mines. Hibernate in caves and mines.

Diet: Emerges at late dusk. Emerging aquatic insects including gnats, crane flies, mosquitoes and mayflies, as well as beetles, moths, bugs, flies. Can eat more than their body weight each night.

Behavior: Lifespan 34 years or more. Forage over water and around trees and lawns. Give birth to one pup which can fly at 14 days. Baby kept beneath wing during day.

Risks: Removal of snags, alterations in riparian areas, timber harvest and forest recreation which causes disturbance. Also closure of cold mines used for hibernation.

Silver-Haired Bat

Silver-Haired Bat (Lasionycteris noctivagans)

Silver-Haired Bat
Image Copyright (c) Merlin D. Tuttle

Description: Body length about 3.6-4.6″, with an 11-13″ wingspan. Black with silver-tipped fur and black wings. Tail membrane is lightly furred close to the body.

Range: Throughout North America, scarce through much of its range. Primarily a forest bat.

Habitat: Roosts singly or in small groups in wooded areas, especially in old growth forests. It typically roosts in hollows, loose bark and cracks and crevices of trees. During migration, may be found in sheds, wood piles, outbuildings and fence posts.

Diet: Mostly feeds on moths, but also true bugs, flies, mosquitoes, termites and beetles. Have been seen flying before the sun has set. Feeds over water and above treetops in woods.

Behavior: One of the slowest flying bats. People fishing have caught this bat on fish hooks. (See FAQ for what to do). Generally give birth to twins which can fly at 4-5 weeks of age. Lifespan 12 years or more.

Risks: Logging and loss of large snags, loss of riparian areas.