Bats in the Desert and the Southwest
Bats are often thought of as flying mice, but they are more closely related to primates, including humans, than they are to mice. Bats are unique among mammals because they fly. As with most other mammals, the bat's body is covered by hair, with the exception of its wings.
Although bats have the same basic arm and hand bones found in humans and most other mammals, the bat's hand and finger bones are very long and slender and there are only four digits. The skin between the arms, fingers, body, legs, and feet looks delicate, but is extremely resistant to tearing by sharp objects.
Size can vary greatly among the more than 900 bats species worldwide, ranging from the 0.5-ounce bumblebee bat with a 6-inch wing span to the 3.3-lb flying fox with a wing span of 80 inches.
Geography – Range
Bats are found almost everywhere on earth, except in extremely hot desert environments and the cold polar regions.
- Weight: 1/2-oz. –3.3lbs.
- Length: Wingspan: 6-78"
- Sexual Maturity: 6-12 mos.
- Mating Season: year round
- Gestation Period: 60-240 days
- No. of Young: 1-2
- Birth Interval: 1 year
- Lifespan: 4-32 years in the wild
- Typical diet: insects
All resident species of bats in the US are capable of being infected with rabies, but the incidence of rabies is the same as in other mammals. Left alone, bats pose no threat to humans. But most bats will bite when captured and handled.
Never handle a bat that appears unable to fly.
Never use your hands to pick up a bat found on the ground.
Before entering a bat roosting site to study specimens, contact the Board of Health and inquire about local rabies conditions.
The more than 900 species of bats worldwide belong to the taxanomic order Chiroptera. The United States is known to have 15 genera, totaling 44 species of bats.
Bats are unique in the animal kingdom because they are the only mammals to have evolved true flight. Most species also possess a system of acoustic orientation, often called "bat radar," but technically known as echolocation.
There are numerous species of bats throughout North America. Those that inhabit the southwestern deserts comprise 11 genera and more than 18 species. The more wide-ranging ones include:
Big Free-tailed Bat (Tadarida macrotis) - Extreme southern Sonoran and Chihuahuan deserts. Free-tailed bats also known as mastiff bats, or bulldog bats because of their facial resemblance to dogs, comprise about 90 species of bats in the family Molossidae. Most species live in groups.
Brazilian Free-tailed Bat (Tadarida brasiliensis), by far the most common bat, occurs throughout the southern US including all four southwestern deserts. A US population of more than 100 million also makes it one of the most numerous of all mammals. Most individuals from this region migrate to Mexico for the winter, usually toward the end of October, and return in March to mate.
California Leaf-nosed Bat (Marcotus californicus) - Sonoran and Mojave deserts.
California Myotis (Myotis californicus) - Throughout all four deserts of the American Southwest and along the Pacific coast.
Cave Myotis (Myotis velifer) - Sonoran and chihuahuan deserts, excluding California.
Ghost-faced Bat (Mormoops megalophylla) - Extreme southern Sonoran and Chihuahuan deserts.
Long-tongued Bat (Choeronycteris mexicana) - Extreme southern Sonoran Desert.
Mexican-Free-tailed Bat - (Tadarida brasiliensis mexicana) - Chihuahuan Desert. A subspecies of the Brazilian free-tailed bat, forms colonies of several million individuals. Females migrate from Central Mexico to Texas and adjacent states each spring, returning south in the fall. Carlsbad Caverns in New Mexico was discovered as a result of the Mexican free-tailed bat's emergence. Here, in five large caves, they form summer nursery colonies, where they produce about 100 million young. While females occupy the nurseries, their daily flights to and from the caverns are a major feature of this national park.
Mexican Long-nosed Bat (Leptoncyteris nivalis) - Chihuahuan Desert of southwestern Texas.
Pallid Bat (Antrozous pallidus) - Throughout all four deserts of the American Southwest.
Pocketed Free-tailed Bat (Tadarida femorosacca) - Extreme southern Sonoran Desert
Sanborn's Long-nosed Bat (Leptoncyteris sanborni) - Sonoran Desert of southeastern Arizona.
Silver-haired Bat (Lasionycteris noctivagans) - Great Basin Desert and across the northern US.
Southwestern Myotis (Myotis auriculus) - Extreme southern Sonoran and Chihuahuan deserts.
Spotted Bat (Euderma maculatum) - Ranges throughout all four deserts of the American Southwest. One of the largest North American bats, this species is also called the death's head bat.
Townsend's Big-eared Bat (Plecotus townsendi) - Throughout all four deserts of the American Southwest and along the Pacific coast.
Vampire Bats - Three species of blood-eating bats, family Desmodontidae, native to the New World tropics, occurring in the Chihuahuan Desert of northern Mexico. Vampire bats feed on any quietly resting warm-blooded animal. They make a small cut with their sharp incisor teeth, often without disturbing their prey, and lap the blood that flows from the incision. The three species are the common (Desmodus rotundus), white-winged (Diaemus youngi) and hairy-legged (Diphylla ecaudata).
Western Mastiff Bat (Eumops perotis) - Sonoran and Chihuahuan deserts.
Western Pipisrelle (Pipistrellus hesperus) - Throughout all four deserts of the American Southwest.
Yuma Myotis (Myotis yumanensis) - Throughout all four deserts of the American Southwest.
As bats fly, they issue a continuous stream of high-pitched sounds at the rate of about 30 per second. The frequency of these sounds starts at approximately 30,000 cycles, the extreme upper limit of human hearing, and ranges upward to 60,000 cycles.
The squeaking of a roosting bat is at a much lower frequency and easily discernible to the human ear. If a bat picks up an echo from one of its sounds, it instantly speeds up the rate of discharge until the signals are coming at 50-60 per second.
The pattern formed by the echoes tells the bat of obstacles, their size, shape, and location. Bats can thus easily locate their prey, night-flying insects, as well. This is referred to as echolocation.
Bat "wings" are really leathery membranes stretched between the extremely elongated four "fingers" of their front feet, extending back to the outer portion of their hind legs. Another membrane extends from the inside of the hind legs to the tail, leaving the hind feet free for gripping as the bat hangs upside down in its roost.
Although the bat is not blind, its eyes are best adapted to seeing in the dark, and they see in black and white only.
Bats have greatly enlarged ears, necessary for night flying, which they keep meticulously clean with their sharp thumbs.
The thumbs of the forefoot are small, equipped with sharp claws and not connected to the membrane.
Bats are very shy creatures and like most wild animals, avoid contact with humans while going about their business of eating, reproducing and avoiding predators. Bats vary greatly in their habits, depending on their species. Some fly in daylight, others at dusk or dawn, and still others only in the dark of night. Some are found exclusively in remote caves, others may even be behind the shutters of your house. Some hibernate while others migrate long distances.
The flight of bats is not direct but undulating, somewhat like a stone skipping across a pond. As it hunts, the bat is virtually unmolested. Occasionally, one may fall prey to an owl, or a sudden storm might claim some victims, but, for the most part, the life of the bat is quite uneventful.
Although their general appearance would seem to deny it, bats are clean. When a bat returns to its roost for its upside-down sleep, it will spend as much as 30 minutes cleaning itself before settling down to sleep. Wherever it can reach with its long, pink tongue will be thoroughly bathed. Often, moistened hind feet with their fingers free of the membrane will tend to the rest of the body.
When winter comes, insects are no longer available and weather extremes make flying hazardous. The bat, having at least doubled its weight since spring, will either hibernate or migrate. Some bat migrations are known to cover as much as 1,000 miles. By late fall, one way or another, the bat has accumulated a layer of fat that will sustain it either through a winter's sleep or a marathon migration flight.
Some species of bats prefer to live alone in trees. Other species live in groups called colonies and are likely to inhabit caves. Tropical bats make homes everywhere from banana leaves to spider webs.
Food & Hunting
Nearly all bats that live in the United States feed on insects. As it flits about, the bat gathers insects in its open mouth or in its tail membrane, which it controls like a scoop. In the course of one night's hunting a bat may consume more than half its own body weight in insects. Bats consume many hundreds of thousands of tons of insects each year.
As it flies across open water, the bat swoops low and dredges up water in its dangling lower jaw. It may make several passes over a pond or rain puddle to reduce its thirst.
Mating may occur two or even three times a year; in late fall, just before hibernation, in midwinter if the roost is warm enough, and again in spring.
The birth, however, following a delayed fertilization where the sperm is held dormant within the female, takes place in the spring or summer after an actual gestation period of 50 to 60 days. While some births occur in May, June and July see the arrival of most baby bats.
When she is about to give birth, the female moves off to an area within the roost and changes her position so that she is hanging head-up by her thumbs rather than head-down. As the infant emerges, the female cups her tail membrane to catch it. She then licks it to help it free its wings and legs, which are stuck to its body.
The young bat may weigh one-fifth as much as its mother. Its eyes are closed for the first day only, and it is quite naked for the first several days. Within a week after its birth the baby bat is carried on the nightly hunts by the female; it grasps her fur and feeds at one of her two nipples.
In two or three weeks it is weaned and then may be fed on regurgitated food brought home by the mother, after it becomes too heavy. By the third or fourth week, it is hunting on its own and is only five weeks away from full growth. Females mate at the end of their first summer, males at the end of their second. In some species, multiple births occur up to four.
A bat may live from 10 to 20 years, depending on species and circumstances. Accidents claim some, cave temperatures that drop below freezing take those that don't move in time, but bats are more likely to live out their full life potential than most small mammals.
Bats have many natural enemies and large numbers of them die while still young. Some of the hazards include great horned owls, some species of hawks, Peregrine falcons, raccoons, house cats, and snakes. Bats can be caught on barbed-wire fences, fall from a roost, or die if their cave is flooded.
The most significant causes of premature bat death, however, are the activities of people. Bats are in serious decline nearly everywhere. Forty percent of the bats in the US and Canada are endangered or candidates for such status. Even small disturbances in their habitat can seriously threaten their survival. Use of insecticides in agriculture is responsible for killing bats in great numbers. When bats consume the chemical-laden insects, the bats become poisoned and die.
Bat droppings (guano) support entire ecosystems of unique organisms, including bacteria useful in detoxifying wastes, improving detergents and producing gasohol and antibiotics.
Photos by Dick Wilkins of Bat Rescue
If you have found a downed bat don't touch it with your bare hands. Using leather gloves or a thick cloth, gently put the bat in a small box with the cloth (so it has somewhere to cling and hide), cover and keep it away from children and pets. Place the box somewhere warm and quiet if possible. If you are in Southern California, immediately call 858/679-0211. If you are not in Southern California, click this link to Bat World's Local Rescue page to find a rehabilitator near you by clicking on your state. If you can't find one there, let Bat Rescue know and they will try to find a qualified bat rehabilitator in your area who can help you and the bat.
Bat Book Gift Set includes: Award-Winning Stellaluna Children's Book with a Toy: Mexican Free-Tailed Bat
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