Background and Characteristics

What do you think of when you hear the word “bats”? Do you think of creepy, blind, blood-sucking animals that fly into your hair? Or do you think of cute, winged mammals that use a type of sonar to navigate and locate insects? Many of the things that people believe about bats are untrue. Because bats are shy and fly at night they are often seen as mysterious. It is said that people fear the most what they understand the least. This lack of understanding along with deliberate destruction of bats and their habitats has caused a worldwide decline in bat populations.

Bats are mammals. They are mammals because they are warm-blooded and have fur. In addition their young are born alive and are fed milk from their mothers. They also have rather complex brains.

There are approximately 1,000 species of bats in the world. They live on every continent except Antarctica. Most bats live in the tropics. Of the 1,000 species, approximately 42 live in North America. Illinois is home to 12 species of bats.

Bats range in size. The largest bats in the world are the flying foxes of Australia and Southeast Asia. These fruit and nectar-eating bats have furry, fox-like faces and wingspans of 6 feet. The smallest bat (and the smallest mammal) in the world is the bumblebee-sized Kitti’s hog-nosed bat from Thailand. It weighs less than a dime, and its body is slightly larger than a jellybean. Most Illinois bats are 2 to 3 inches long and weigh ¼ to ½ of an ounce.

Bats are the only mammals that can actually fly. Their forearm and hand evolved into a “hand wing,” which is the meaning of the order’s name Chiroptera. Their wings are made of thin sheets of muscle and elastic fibers covered by skin. The bones of the arm, second to fifth fingers, and back leg support the wing. The first finger, or thumb, is like a claw. It is used for crawling, grooming, holding and catching food, and fighting (See Figure 1).

Most bats, including all Illinois bats, are nocturnal (active at night). They rest during the day by hanging upside down by their toes. The weight of their bodies causes their toes to automatically lock into place. Bats even give birth while hanging upside down.

Contrary to popular belief, bats are not blind. Bats have good eyesight. In fact, bats can see better than humans in the dark. Despite their good eyesight, insect-eating bats use a type of sonar called echolocation to navigate and locate prey. Fruit-eating bats do not use echolocation. Instead they rely entirely on their vision when flying in search of food.

Feeding and Locating Prey

Of the 1,000 species of bats in the world, 70% are insectivorous. All Illinois bats are insectivores. Prey for Illinois bats includes mosquitoes, mayflies, beetles, and moths. They forage above streams and ponds (or even swimming pools), along forest edges, and around street lamps and yard lights. They are active at night, hunting for food. They do not use their eyes to find their food. Instead, they use echolocation.

A bat’s sonar system works in the following manner:

a) As a bat flies, it sends out high-pitched squeaks through its mouth and nose that the human ear cannot detect. The squeaks are sent out at a rate of 10 to 20 per second and travel through the air as sound waves.

b) When a sounds wave hits an object in the bat’s path, part of the wave bounces back to the bat. This is the echo that the bat picks up in its highly sensitive ears.

c) The bat’s brain quickly checks the tone and loudness of the echoes and comes up with a great deal of information. Within milliseconds, the bat knows these facts: the location of the object, the speed and direction in which the object is moving, and the type, size, and nature of the object.

d) If the object is an insect, the bat increases the rate of its squeaks. As the bat closes in on the insect, it may be sending out as many as 200 squeaks per second.

Bat echolocation systems are very accurate. They can detect an insect as small as a gnat. They can also detect very thin wires and objects as fine as a human hair. Bats can distinguish one type of insect from another. They can determine if it is a fat, hairy caterpillar or a hard-shelled beetle. Bats can echolocate tree branches, buildings, automobiles, people, and other large objects from up to 50 feet away.

Some moths can hear the high-pitched squeaks that are put out by bats and therefore have a better chance of escaping. Some moths can even create sounds in the same high-pitched frequency that is used by bats. If they hear a bat, they send out bursts of sound and “jam” that bat’s navigational system.

Bats catch and swallow insects without a break in flight. Sometimes the bat catches the insect in its mouth. Other times, the bat reaches out with its wing tip and snatches the insect from the air. The prey is then quickly placed in the bat’s mouth. The bat’s small razor sharp teeth then finish it off.

It takes a lot of energy to fly around and catch insects. Therefore, it is necessary for bats to eat a lot. One bat eats up to 6,000 insects in one night. (A colony of 20 million Mexican free-tailed bats in central Texas eats up to a half million pounds of insects every night.)

There are many other bats living throughout the world that do not eat insects. Throughout the tropics, fruit-eating bats are very important in seed dispersal. Nectar eating bats are absolutely necessary for the pollination of countless trees and shrubs. Forty percent of tree species depend on bats for seed dispersal or pollination. On the savannahs of East Africa, the giant baobab is known as the “Tree of Life” because so many other plants and animals depend on it for their survival. But the tree itself is dependent on bats. Its showy white flowers open only at night and are specially adapted to be pollinated by bats. Without bats the baobab could die out, triggering a chain of extinctions. In the Sonora Desert of the southwestern U.S., long-nosed bats play a similar role in the lives of several cactus species. Bananas, avocados, dates, figs, peaches, mangos, guavas, cashews, cloves, and tequila are all products that depend on bats for pollination and thus their survival. Chicle latex used in chewing gum, manila and sisal fibers used for rope, and kapok used for bandages and life preservers all come from plants that depend on bats for their survival.

There are also bats that feed on blood. These are called vampire bats. There are no vampire bats in Illinois; they all live in tropical America. They do not feed on human blood. Instead they feed on blood from large birds and mammals (pigs and cattle). They do not sink their teeth into a mammal’s jugular vein. Instead they scratch the skin open and lap up the blood with their tongue. A chemical in their saliva prevents the blood from clotting. Vampire bats will feed on the blood for 20 to 30 minutes and then retreat to their roost. Their nightly meal consists of about 2 tablespoons of blood. The host animal usually does not wake up during the bats’ feeding.

Bats drink water by skimming along streams and ponds while in flight.

Roosting, Hibernation, and Migration

Bats use a variety of daytime roosting sites. Some roost in old buildings, caves, and abandoned mines. Others use trees, roosting inside cavities or underneath bark, or by hanging among the leaves. Females and their pups roost in either solitary family groups or large maternity colonies. Males roost singly or in small bachelor colonies.

As autumn approaches bats are not able to find the food necessary to survive, so they migrate to hibernation sites (hibernacula), which are primarily caves or abandoned mines. In preparation for hibernation, bats accumulate large quantities of body fat, which allows them to survive winter in a torpid (inactive) state. Bats remain in hibernation for at least 6 months, but they arouse intermittently to drink moisture from cave walls and condensation droplets on their fur. They may even emerge and hunt for insects during warm spells. A bat’s heart rate can be 1000 beats per minute during flight but during hibernation it drops to 5 beats per minute. Also, its body temperature drops from over 100 degrees Fahrenheit to 40 degrees Fahrenheit. Other bats migrate far enough south to remain active all winter. In the spring, bats return to their summer home where they will again feed at night and rest during the day. May 15^th to August 15^th is considered to be the length of their stay during summer in Illinois, depending on whether they live in the northern or southern zone. A colony of Indiana bats in Cass County, Illinois, was documented to stay in its summertime roost until October 4^th.

Little brown bats are the most common bats in our area. As with all bats, they mate in the fall but do not become pregnant until April. After a winter of hibernation, little brown bats begin their migration to summer roosting sites and may live in maternity colonies of 300 to 600 females. They give birth in June or July to one pup. The pup immediately uses its large thumbs to climb up to the mother’s teat. The baby will not open its eyes for two days. At dusk, mothers leave their young behind in the roost and return between feedings to nurse their young. They are able to recognize their baby among several hundred others by its smell and individual chirping call. In about 3 weeks the young bats are ready to fly. They will still nurse for one week while they learn how to hunt.

The Rabies Misconception

One of the most common misconceptions about bats is that they are all rabid (carry rabies). This statement is very untrue. It is estimated that less than one-half of one percent of all bats contract rabies. Cats, skunks, foxes, and raccoons are more likely to carry this disease. Over the last four decades, only 15 people in the United States and Canada have contracted rabies from bats. More people die annually from dog attacks, bee stings, or even being struck by lightning. Bats that are found on the ground are usually sick or injured and should be left alone, as any wild animal should. People are in danger when they try to foolishly pick up a bat, which may bite in self-defense.

Bat Conservation

Bats are among the most gentle and necessary animals on this earth. They inhabit almost every habitat throughout the world, consuming insects, pollinating plants, and dispersing seeds. Bat research has helped in the design of navigational devices for the blind and has also aided in the development of vaccines and other medical advances. The droppings of bats (guano) are collected and used as fertilizer. For these reasons and more, bats are important to humans. However, bats suffer from habitat loss, pollution, poisoning, and predators as many other animals do. Predators such as hawks and owls eat bats, but humans are by far their worst enemies. Destruction of rain forests and caves and spraying of insecticides threaten the survival of many bat species. Fear and ignorance has resulted in the unwarranted destruction of bats for centuries.

In Illinois, four of the twelve species of bats are endangered. The Indiana bat and gray bat are federally endangered, while the southeastern bat and Rafinesque’s big-eared bat are state endangered. State and federal endangered species laws protect endangered bats. In addition, all bats are protected under the Illinois Wildlife Code. To protect individual species it is necessary to protect their habitat. Protecting caves is a high priority. The Illinois Department of Conservation has posted signs at several caves restricting access when bats are present. In Illinois and elsewhere, Bat Conservation International has installed metal gates at the entrances of several important bat caves. They allow entrance by the bats that use the caves but restrict entry by humans. There is also an effort to prevent the sealing of abandoned mines used by bats. Likewise, the preservation of forested areas is important. If bats survive the many problems that they face, they can live to be 25 to 30 years old.

You can become involved by not disturbing bats during critical times when they are hibernating or rearing young, by educating others of the importance of bats, and by supporting efforts by government agencies and conservation organizations (Bat Conservation International) devoted to helping the preservation of bats.

Bat Conservation International's logo comes from an ancient Chinese design, called the wu-fu symbol. In Chinese, the word for bat and the word for good luck have the same sound, fu. Wu is the word for five, and each of the five bats in the symbol represents one of the five elements-earth, air, fire water, metal-as well as one of the five happinesses- health, wealth, long life, good luck, tranquility. (Representations of these elements and happinesses vary throughout Chinese philosophy.) The stylized bats are commonly depicted in red, the color of joy, and they surround a prosperity symbol. The five-bat wu fu symbol appears frequently in Chinese literature and art.

People can also construct bat houses to provide additional roosting sites for bats. Any bats that roost in crevices or are found in buildings and under bridges are likely tenants for houses. The little brown bat and big brown bat can be found in our area using bat houses. A bat house is similar to a birdhouse, but the opening is in the bottom.

Some sources say that a purple martin can eat up to 1,000 mosquitoes a day. A single big brown bat can eat 3,000 to 7,000 mosquitoes each night. Since bats are such an important form of natural control for insect pests like mosquitoes, it is in our own best interest to perpetuate them. This is already being done in much of Europe where bats are totally protected and where people build bat houses much like we build martin houses.

The most likely occupants of bat houses in Illinois are the big brown bat and little brown bat. The most critical dimension is the three-fourth-inch width of the entry space. All inner surfaces must be roughened with a chisel or saw cuts to permit bats to climb on them with ease. Rough outer surfaces are also preferred.

Daytime temperatures in the bat house must be very hot – about 80° to 90° F. One way to achieve this is to cover the bat house on top and extending a couple inches down the sides with two or more layers of tarpaper. The dark color of the tarpaper absorbs heat from the sun and helps protect bats from the rain. The tarpaper may be hard to attach and may weather badly. Another alternative would be to paint the bat house black so it would absorb heat from the sunlight.

Bat houses should be securely fastened to a tree trunk or the side of a building roughly 12 to 15 feet above the ground. Preferably they should be on the east side of the house or tree where they will receive the morning sun but will be shaded during the afternoon. Bats also seem to prefer sites that are protected from the wind.

The best habitat for bat houses is relatively near rivers, lakes, bogs, or marshes where insect populations are high. The closer bat houses are to such places, the greater probability they have of being used. Those located more than a half mile from these habitats have a low probability of being used.

Bat houses should be placed by early April, but it may take a year or two for bats to find the house. Once used, it does not need to be cleaned. Chances of occupancy are better if bats already live in nearby buildings.

Sometimes bats create severe problems for people by establishing huge colonies in the attics of homes. The best way to solve this problem is to hire a carpenter in the winter to exclude bats at the holes where they enter the house. Since most bats migrate, it is possible to exclude the bats while they are not present.

The Illinois Department of Conservation and Dr. Merlin D. Tuttle of the Milwaukee Public Museum in Milwaukee, Wisconsin have provided this bat house information.

Species Accounts

Illinois bats are divided into two categories: tree bats and cave bats.

Tree Bats

Tree bats are more solitary than cave bats. They roost singly or in small family groups. They migrate in response to cold weather but seldom enter caves to hibernate. The fur of tree bats seems much more colorful than that of cave bats. In addition, there is fur on the membrane between the legs and tail.

Hoary Bat (Lasiurus cinereus)

1.0 oz, 13 - 16 inch wingspan, hair tips are white giving a frosted (hoary) appearance. These are the largest and most colorful bats in Illinois. They are strong, fast flyers that often migrate in large groups. Hoary bats usually have 2 pups.

Red Bat (Lasiurus borealis)

0.5 oz, 11 - 13 inch wingspan, bright red-orange to yellow-brown fur. Very common, found in every county in Illinois during the summer. Solitary, roost in low leaves of trees. Have 1 to 5 pups.

Silver-haired Bat (Lasionycteris noctivagans)

Less than 0.5 oz, 11 – 13 inch wingspan, bear-like face and beautiful dark, silver-tipped fur on its back. Found sporadically throughout Illinois in forested habitats. Have 2 pups.

Cave Bats

Cave bats hibernate during winter in caves or abandoned mines. They are also social, often forming groups of thousands. Even during summer roosting they tend to live in large groups called maternity colonies. These bats have no hair on the membrane between their legs and tail. In general, these bats are less colorful than the tree bats.

Evening Bat (Nycticeius humeralis)

0.4 oz, 10 – 11 inch wingspan, brown fur with black membranes and ears, usually have 2 pups, closely resembles big brown bat but evening bat is much smaller

Little Brown Bat (Myotis lucifugus)

0.35 oz, 9 to 11 inch wingspan. Fur ranges in color from pale tan to reddish or dark brown. These are perhaps the most common bats in Illinois. They far outnumber any other hibernating bat in Illinois during winter, with groups consisting of tens of thousands. Have 1 pup.

Gray Bat (Myotis grisescens)

0.3 oz, 11 – 13 inch wingspan, uniformly gray in color. Not common in Illinois, federally endangered. Have 1 pup.

Eastern Pipistrelle (Pipistrellus subflavus)

0.2 oz, 8 – 10 inch wingspan, smallest Illinois bat, orangish-tan tipped black fur, rarely seen because of their small size. Have 2 pups.

Indiana Bat (Myotis sodalis)

0.25 oz, 9 – 11 inch wingspan, fur is dull black-charcoal at the base with cinnamon at the tips. These bats can be confused with little brown bats, however they are much less common and are rarely seen. Federally endangered due mainly to disturbance to hibernation sites and destruction of summer habitat. Have 1 pup.

Comparison:

Indiana Bat on the left. Little Brown Bat on the right.

Southeastern Bat (Myotis austroriparius)

0.25 oz, 9 – 11 inch wingspan, wooly dark fur with orange tips, fur on under parts is more whitish, nose is pinker than other bats. Endangered in the state of Illinois, very few individuals ever found in Illinois. Have twin pups.

Northern Bat (Myotis septentrionalis)

0.2 oz, 9 – 11 inch wingspan, brownish fur, overall small in size with larger ears. Have only 1 pup.

Big Brown Bat (Eptesicus fuscus)

0.4 to 0.8 oz, 13 – 16 inch wingspan, second in size only to the hoary bat. One of the most common bats in Illinois, frequently found in houses, most likely species to occur in urban areas. Have 2 pups.

Rafinesque’s Big-eared Bat (Corynorhinus rafinesquii)

0.33 oz, 10 – 12 inch wingspan, grayish fur with whitish under parts, easily distinguished from other bats by large conspicuous ears. Distribution of this species is limited to extreme southern counties in Illinois; therefore it is listed as endangered in the state of Illinois. Have 1 pup.

Pictures used with permission from Bat Conservation International. All photos protected by copyright.