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No other mammals in the northeast are as misunderstood as bats. A variety of myths and misconceptions surround these small, nocturnal, flying mammals. Many people think of bats as vicious animals that carry diseases and get tangled in hair. Others consider them to be friendly, cuddly animals that need only our love and understanding. Both images are somewhat misguided. This publication will describe the important role that bats play in our environment and will explain what to do if you find yourself sharing living quarters with them. It will also discuss the reality behind the most commonly held misconceptions surrounding these beneficial mammals.
Bats make good neighbors. As the only major predators of night-flying insects, bats play an important role in controlling many insect pests. A single bat can consume as many as 500 insects in just one hour, or nearly 3,000 insects every night. A colony of just 100 little brown bats, the most abundant species in the Northeast, may consume more than a quarter of a million mosquitoes and other small insects each night.
Big brown bats, which live primarily in agricultural areas, feed on June bugs, cucumber beetles, green and brown stink bugs, and leafhoppers. Research has shown that over the course of a summer, a colony of 150 big brown bats can eat 38,000 cucumber beetles, 16,000 June bugs, 19,000 stink bugs, and 50,000 leafhoppers and can prevent the hatching of 18 million corn rootworms by devouring the adult beetles.
The red, hoary, and silver-haired bats help to maintain forest health in the region by feeding on forest pests such as tent caterpillar moths. Because of their role in controlling insect numbers throughout the Northeast and elsewhere in the United States, the maintenance of wild bat populations is important for maintaining ecosystem health.
Nine species of bats live at least part of the year in the northeastern United States, and two southern species reside infrequently in Pennsylvania. Northeastern bats range in size from the hoary bat (length 5.1 to 5.9 inches from nose to tail; wingspan 14.6 to 16.4 inches; weight 0.88 to 1.58 ounces) to the pipistrelle bat (length 2.9 to 3.5 inches; wingspan 8.1 to 10.1 inches; weight 0.14 to 0.25 ounces). Colors range from the drab brown of the little brown bat to the striking frosted red coat of the red bat. Although some mammals are able to glide, bats are the only mammals that truly fly. That is, they actually flap their wings to propel them in flight. They belong to their own unique order of mammals, called Chiroptera, meaning “hand wing,” which refers to how the finger bones of a bat support its wings. The wings of a bat are actually thin membranes of skin that stretch between the fingers of the front leg and extend to the hind legs and tail. The bat’s finger bones are greatly elongated and serve a purpose similar to struts on an airplane wing, providing support and maneuverability during flight. When at rest, a bat folds its wings alongside its body to protect the delicate finger bones and wing membranes.
Bats live in a variety of habitats, including wetlands, fields, forests, cities, suburbs, and agricultural areas. They usually feed in areas where insects swarm, such as over water and agricultural fields, in forest clearings and along forest edges, and around street lights.
All northeastern bats eat insects and take their prey on the wing. Bats use their mouths to scoop small insects out of the air. Larger insects are often disabled with a quick bite and then carried to the ground or to a perch for eating. If an insect takes last-second evasive action, a bat can flick out a wing to nab the insect and draw it into its mouth. This maneuverability makes bats very efficient insect predators: A bat may consume nearly 50 percent of its body weight in insects in a single night!
Although bats can see quite well, they rely on their hearing for night flying. A highly sophisticated adaptation, called echolocation, enables bats to use their large and well-developed ears to navigate and catch prey in total darkness. A bat’s echolocation system makes use of ultrasonic sound pulses and echoes to locate objects. Bats open their mouths in flight and emit a series of ultrasonic sound pulses. These pulses bounce off nearby objects—such as bushes, fences, branches, and insects—then return as echoes to the bat’s ears. Using the information gathered from these echoes, a bat can maneuver to capture an insect or avoid flying into an object.
Bats have one of the lowest reproductive rates for animals their size. Most northeastern bats have just one or two pups per year, and many females do not breed until their second year. This low reproductive rate is partially offset by their long lifespan. On average, bats live approximately four to six years, and there are some incredible records of bats living twenty to thirty years in the wild.
Most bats mate in late summer or early fall. However, the male’s sperm remains dormant in the female’s reproductive system until spring, at which time the female ovulates and fertilization occurs. The pups are born approximately six to eight weeks later, during late May and early June.
Because few flying insects are active during the winter months, bats that remain in the Northeast year-round gather in caves and abandoned mines to hibernate. Hibernation is a state of prolonged torpor during which bats greatly reduce their normal metabolic activities. Body temperature in hibernating bats falls from a normal level of more than 100° F to that of the surrounding cave temperature, usually 40-50° F. The heart rate slows to only about twenty beats per minute, as compared to 1,000 beats per minute during flight. By allowing their bodily processes to slow this way, hibernating bats can survive on a very small amount of stored fat during the five- to six-month hibernation period, losing from one-fourth to one-half of their pre-hibernation weight.
Bats arouse from hibernation during March and usually arrive at their summer roosts in April. At this time, pregnant females seek out sheltered roosts in rock crevices, tree cavities, and tree foliage in which to rear their pups. Female red, hoary, and silver-haired bats roost alone during the summer, while females of other species gather into large or small groupings called maternity colonies. Male bats usually roost alone in fairly exposed locations.
Depending upon the species, females give birth to one to three pups in late May and early June. The pups, which are born hairless, blind, and helpless, cling tightly to their mother in the maternity roost. On summer evenings, females leave the pups in the roost and hunt insects nearby, returning often throughout the night to nurse their offspring. As the pups grow older, the females return less frequently during the night. The pups begin to fly and hunt on their own by mid-July when they are approximately five weeks old. However, the pups will continue to nurse until they can adequately feed themselves.
Maternity colonies begin to disband in late summer and early fall. At this time, males and females of hibernating species begin to swarm together. Large groups of these bats will swarm in and out of cave entrances throughout the night, often roosting in the caves during the day. This swarming behavior brings adults together for mating, and may also teach young bats the location of the hibernation caves. Autumn also prompts the silver-haired, red, and hoary bats to begin their migration to warmer climates.
There are primarily two scenarios in which humans and bats find themselves in conflict:
The proper techniques for dealing with these uninvited visitors will be outlined in the following sections.
Individual bats occasionally enter houses, most often during summer evenings in mid-July and August. These wayward bats are usually pups that are just beginning to fly. Fortunately, these incidents can be dealt with quite easily. A bat flying in the house will usually circle a room several times in search of an exit. The best method for getting a bat out of the house is to allow it to find its own way out. Chasing or swatting at the bat will cause it to panic and fly erratically around the room, which needlessly prolongs the incident.
If you do encounter a bat flying in a room, follow this procedure:
If the bat tires and comes to rest on a curtain or wall, you can easily remove it without directly touching it. Follow the steps below, and remember to never handle a bat, or any other wild animal, with your bare hands.
If you have recurring problems with bats entering your home, you may want to inspect your attic to determine if you are housing a bat maternity colony.
Most bats in the Northeast roost in secluded locations away from humans, but two species, the little brown bat and the big brown bat, often attract attention because they repeatedly roost in buildings. These bats once roosted in hollow trees but adapted to roosting in human structures after early settlers eliminated large expanses of forests. These ‘house bats’ situate their roosts in hot attics, which act as incubators for the growing pups.
Because they live in such close quarters with humans, unique challenges are involved in the conservation of house bats. House bats have only one or two pups per year, so the protection of their maternity colonies is important to the survival of these beneficial mammals. The destruction of just one maternity colony through chemical extermination or vandalism can have a long-term impact on the populations of both bats and insects in a local area. Unfortunately, homeowners often consider maternity colonies a nuisance and may mistakenly believe that extermination or destruction of the colony is their only solution. There is, however, a safe, humane, and effective procedure for removing a bat colony from a building. This procedure, called bat-proofing, is described in the following sections.
One way to tell if you are sharing your house with a bat colony is to simply go into the attic and look for roosting bats. During the day, bats will likely be roosting in narrow crevices in the attic walls, between the rafters, or tucked into the space between the rafters and roofing material. When you enter the attic, the bats will quickly retreat out of sight (rather than taking flight). If you can’t see them, listen for the squeaking or scurrying sounds that will verify their presence.
If you are uncomfortable entering the attic when bats may be present, you can inspect the attic at night for bat droppings. The dry, black droppings are about the size of a grain of rice and accumulate in piles below areas where the bats roost. (Mouse droppings look similar, but you would find them scattered in small amounts throughout the attic.) If you find bats living in your attic during the day, or if you find large accumulations of bat droppings, then you probably have a maternity colony in your house.
Sometimes, when homeowners understand the important role that bats play in controlling insects, they decide to allow the colony to remain in the attic or eaves. In this case, the homeowner must seal all openings that would give bats access into the living spaces. This safety measure is particularly important for families with small children and pets.
If you have a bat colony in your attic and you want to remove it, you must use the proper methods to do so. Do not use chemical poisons or repellents to eliminate a bat colony. Poisons often scatter dead, dying, or disoriented bats throughout the house and neighborhood, which increases the risk of children or pets coming into contact with sick bats (Constantine 1979). Repellents, such as moth balls or flakes (naphthalene), sulfur candles, or electromagnetic or ultrasonic sound devices do not permanently remove bats from a home. Unless their entrances are sealed, the bats will return as soon as the chemical repellents wear off.
The best way to safely and permanently evict a maternity colony is to seal all of the colony’s entrances. This inexpensive procedure, called bat-proofing, is described in the following sections.
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