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Bats, the only mammal that can fly, are highly beneficial to people and the advantages of having them around far outweigh any problems you might have with them. As predators of night-flying insects (including mosquitoes!), bats play a role in preserving the natural balance of your property and maintaining healthy ecosystems.
A study published in Science estimates that insect-eating bats provide a significant pest-control service, saving the U.S. agricultural industry at least $3 billion a year. For example, the 1 million little brown bats that have already died equates to between 660 to 1,320 metric tons of insects that are not being eaten each year.
Although swallows and other bird species consume large numbers of flying insects, they generally feed only in daylight. When night falls, bats take over. A nursing female little brown bat, for example, may consume her body weight in insects each night during the summer.
Contrary to some widely held views, bats are not blind and do not become entangled in peoples' hair. If a bat comes close to your head, it's probably because it is hunting insects that have been attracted by your body heat. Bats are occasionally found in homes and camps and should be submitted to the Public Health Lab for rabies testing if they come in contact with a person. Approximately 4 out of 100 bats tested are positive for rabies each year in Maine.
There are eight bat species in Maine. Some bat species hibernate in Maine during the winter, called hibernating bats, and other bat species migrate south for the winter, called tree bats. The eight bat species present in Maine are:
- Big brown bat (Eptesicus fuscus)
- Little brown bat (Myotis lucifugus)
- Northern long-eared bat (Myotis septentrionalis)
- Eastern small-footed bat (Myotis leibii)
- Tri-colored bat (Pipistrellus subflavus)
- Hoary bat (Lasiurus cinereus)
- Silver-haired bat (Lasionycteris noctivagans)
- Eastern Red bat (Lasiurus borealis)
Maine’s bats occupy a variety of habitats including wetlands, ponds, forests, fields, and even mountain slopes. Prior to the listing myotis bats as Threatened or Endangered in 2015, very little was known about the habits of bats in Maine. Since the listing, MDIFW has increased research, conservation, and protection efforts for both Maine’s bat species and their vital habitats. One recent study by the Department, in collaboration with the University of Maine and Acadia National Park, has documented bats overwintering in talus slopes, which is a pile of rocks that are deposited at the base of cliffs or slopes. The rock piles create crevices and cracks that extend below the surface. Myotis and big brown bats have been documented during the winter on talus slopes using acoustic recording devices. Research is ongoing to determine what specific features of talus slopes make sites potentially more suitable for overwintering bats. The Department continues to search for additional hibernation sites, also known as hibernacula, in the state and is interested in hearing from the public about any bats found at any time of the year. Click here to report a bat colony online.
Bats must cope with cold weather conditions and low food supplies for more than half of the year (October-April). Hibernation sites, or hibernaculum (plural hibernacula), includes cavities in large trees, caves, mine shafts, tunnels, old wells, rock talus, and house crawl spaces or attics. The hibernaculum protects bats from predators, light, noise, and other disturbances. Temperatures in the hibernaculum must be cool enough to allow bats to maintain a low body temperature but not freeze and humidity must be high and constant enough to prevent bats from dehydrating. Bats hibernate alone or in groups, depending on species and enter hibernation sites in late September or October. Maine lacks large cave systems and has few known hibernacula that were once used by hundreds of bats. However, since the introduction of white nose syndrome to the Northeast, the bats surveyed in the known hibernacula have been reduced to a handful of bats during the winter. Learn more about white-nose syndrome.
Figure 3: Drawing Credit - ODIFW
Maine bat species eat vast quantities of night-flying insects, including moths, beetles, mosquitoes, and flies. Most bats hunt in flight or hang from a perch and wait for a passing insect to fly or walk within range. Northern long-eared bats will glean or capture their food off tree foliage. Bats primarily rely on a radar system known as echolocation to locate prey. The bat emits high-pitched sound waves that strike an insect and then bounce back. The bat interprets the reflected sounds to locate the prey. When flying, a bat often scoops insects into its tail or wing membranes, then transfers the insects to its mouth (Fig. 3). This habit results in the erratic flight that people see when they observe bats feeding in the evening. Bats will fly from half-a-mile to six-miles from their roost to a feeding site, using temporary roost sites there until returning to their main roost.
Bats are the only true flying mammals. They belong to the mammalian order Chiroptera, which means "hand-wing." The bones in a bat's wing are homologous, meaning the bone structure of bats is very similar to humans, but bat finger bones are greatly elongated and connected by a double membrane of skin to form the wing, allowing a different function to the structure. Like all other mammals, bats have hair, give birth to live young, have mammary glands which produce milk for their young, and breath oxygen.
Bats range in length from the two-and-a-half-inch long Tri-colored bat, formerly known as the Eastern pipistrelle bat, to the six-inch long hoary bat. The hoary bat has a body approximately the size of a house sparrow and a wingspan of 17 inches.
Though bats have excellent hearing and eyesight, bats primarily use echolocation when navigating their surroundings and foraging for food. The soundwaves emitted by the bat bounce off objects in their environment, returning to the bat at different rates signifying the distance, shape, exact location and movement of the object (or prey). Bats frequencies are finely tuned and recognize their own call so there is no confusion when multiple bats are foraging in an area. These calls are also modified by individual bats, emitting different soundwaves when foraging, social communication and navigation.
Bats are well known for being a nocturnal species, coming out to hunt just before dusk and reentering their roosts around dawn. The safest way to view and enjoy bats is to watch them in action. Bats are fascinating flyers, zigging and zagging about as they chase and eat insects. Little brown bats and tri-colored bats hunt over water. Big brown bats are often seen hunting along the margins of wooded areas or silhouetted against the lighter sky as they twist and turn high above the tree canopy.
It's also fun to watch bats drink, which they usually do first thing after leaving their day roost. They scoop up mouthfuls of water with their lower jaws as they fly over lakes, streams, ponds, or water troughs. Most bats do not come out to eat or drink in heavy rain or when the air temperature remains below 50 degrees Fahrenheit.
To View Bats, Follow These Tips:
The best places to see bats in flight are places where night-flying insects abound, such as next to a stream, lake, or pond; over a meadow or large lawn; along a forest edge; or around bright street or porch lights. Choose a warm summer evening and a site where bats have been spotted flying, or a known roost site from which they will emerge, such as an attic, old barn or bat house. Remain still and quiet; and listen for the squeaks or clicks that many bats make before emerging. Some species of bats begin their night flights 20 to 30 minutes before dark. The common big brown bat may be out foraging earlier. Other species don't emerge until after dark. With the aid of an inexpensive commercial bat detector, listen for the echolocation calls bats make when navigating and locating prey.
Summer is an important time of year when bats eat a significant number of insects every night, preparing for a long winter of hibernation or a lengthy migration to warmer areas. With few to no flying insects available to them during winter in Maine, bats survive by hibernating, migrating to regions where insects are available, or a combination of these strategies.
During hibernation, metabolic activities are greatly reduced. A bat's normal body temperature of around 100 degrees Fahrenheit is reduced to just one or two degrees higher than that of the hibernaculum, and the heart rate slows to only one beat every four or five seconds. A hibernating bat can thus survive on only a few grams of stored fat during the five- to six-month hibernation period.
Banding studies indicate that little brown bats will migrate 120 miles between hibernacula and summer roosts, and, if undisturbed, they occupy the same site year after year. They select areas in the hibernaculum where there is high humidity (70 to 95 percent), and the temperature is 34 to 41 degrees F. Still, there are some species, such as the big brown bat, that can hibernate in relatively exposed situations in buildings where there is considerable fluctuation in temperature. Hibernation lasts until April or early May.
It is important not to disturb hibernating (or roosting) bats. If a bat rouses early from hibernation, it must use its fat reserves to increase its body temperature. A single disturbance probably costs a bat as much energy as it would normally expend in two to three weeks of hibernation. If disturbed multiple times, hibernating bats may starve to death before spring.
Because some bats hibernate in buildings during the winter months, bat-proof a building only when you are sure no bats are hibernating in it. If bats are found hibernating inside after October 15, they should be left alone until early spring (prior to the birthing period in May) after the weather has warmed enough for insects to be out regularly. Meanwhile, seal all potential entry points into human living spaces, and develop a plan so the exclusion process can be accomplished effectively in spring. Learn more about preventing conflicts.
Reproduction & Family Structure
Maine's bats breed in early fall and research shows that bats tend to breed at a hibernation site. Females store sperm until the following spring, when fertilization takes place after they rouse from hibernation (this is called delayed fertilization). Most bat species produce one pup in May, June, or July; the specific dates depend on the species, locality, and weather. The young, called pups, are born and raised in nursery colonies occupied only by breeding females and their young. (Males roost alone or in small groups during this time, leaving the warm roosts and optimal feeding grounds for females). Female big brown and little brown bats often use attics as nursery sites because these areas maintain the warm temperatures, from 85 to 104 degrees F, needed for raising young. The heat speeds the development of the fetus before birth and growth of pups after birth. In the nursery, the young remain with their mothers and suckle frequently. Pups are unable to fly for about a month, so the mother leaves her pup behind when she hunts at night. It is important not to disturb a maternity colony in the spring, when flightless young are present. Panicked females may abandon their young or drop them to their deaths. Female bats may return to the exact place of their birth year after year.
Survival & Threats
Bats have few predators. Hawks, owls, house cats, and raccoons occasionally prey upon them. Natural events including long winters and fierce storms during migration can kill bats. Human activities, including habitat alteration, commercial pesticide use, control practices, and wind power development, are major causes of mortality. Bats can die from direct exposure to pesticides or by eating sprayed insects. For their size, bats are the world's longest-lived mammals. According to records, one big brown bat lived in the wild for 19 years, and a little brown bat reached the age of 33.
A fungal disease that spread from a bat hibernaculum from New York called white-nose syndrome (WNS) is causing the decline of several hibernating bat species in North America, including in Maine. MDIFW, in partnership with USFWS, installed a bat gate at the largest bat hibernacula in Maine, preventing humans from entering the cave and disturbing bats. Learn more about the disease and WNS in Maine.
Management & Conservation
Bats are afforded special protection in Maine. Maternity roost trees and bat hibernacula are protected from disturbance, including no entry to hibernacula by the public during the winter (October 1 - April 30). Bats are not allowed to be excluded from unoccupied buildings during the maternity season (June and July). The Department provides recommendations during the environmental review process to avoid or minimize negative impacts of development on bats. MDIFW recommends siting development away from key habitats where bats aggregate and seasonal wind turbine curtailment measures to minimize mortality of bats.
The Department has attempted several different types of surveys in the past to better understand the status and population trends of bats in Maine. Bats are notoriously difficult to study- they are active at night, they are challenging to catch, and it takes a lot of effort to find bats these days. Luckily, specialized acoustic detectors record high frequency bat calls and software, paired with a keen eye, can help interpret the calls to determine species.
During the summer, the Department conducts stationary surveys using bat detectors throughout diverse habitats in the state. These surveys can identify which species are in the area as well as show evidence of reproduction. When conducted over a long period of time, biologists can better understand population trends of bats in Maine.
During the fall/winter/spring, MDIFW has been using acoustics and other methods to determine whether bats are hibernating in rocky talus slopes. Our work has indicated that myotis and big brown bats are using talus slopes to over-winter in coastal and inland areas. Research is ongoing to pinpoint where on the talus slopes bats are emerging from and what small and large-scale site characteristics are associated with bats.
Approximately every three years, biologists visit hibernacula in the winter to count bats, identify species, and look for any evidence of disease. Since white-nose syndrome, biologists minimize their disturbance to bats by surveying the caves less frequently. Cave surveys are one of the primary indices used to estimate population changes, such as declines due to white-nose syndrome. Some of our cave surveys go back to the 1980s, which is particularly valuable for understanding the status of bats historically.
Another source of data the Department monitors for population trends are the bats submitted to the Public Health Lab for rabies testing. When a bat is handled by a person with bare hands or found in a room with a child or sleeping, person with a disability, or intoxicated person, then it is recommended that the bat is captured and submitted for rabies testing. Little brown and big brown bats are commonly called house bats, because of their affinity for human structures. Historically, little brown bats were common, sometimes found in people’s houses, and tested for rabies. After white-nose syndrome, we saw a similar drop in little brown bats submitted for testing as found in caves.
The Department still collects Colony Reports from the general public. If you have a bat colony, try to do an exit survey by counting the bats that come out around dark. Conduct a survey in early June and then again in late July to see if your count goes up after the pups can fly. Colony Reports can be submitted online.
How You Can Help Bats:
- Minimize pesticides on lawns and gardens - all eight species of bats that live in Maine eat insects. This also helps our bees and other important pollinators.
- Keep standing dead trees on your property (aka snags). As a tree starts to die, bark separates from the tree and creates little spaces which bats use for roosting (daytime resting). Snags and eventually logs provide habitat to lots of other living things (e.g., fungus, birds, insects, salamanders, etc.).
- Maintain some mature forest on your property. Tree bats (Red, Hoary, and Silver- haired) roost in tree foliage of older trees. Older trees also can provide cavities and flaky bark for roosting.
- Spread the message that bats provide a lot of benefits like insect control.
- Prevent bats from getting into your home by sealing off cracks or holes (1/2 inch or larger). Common entry points used by bats: Down chimneys and where chimneys and other masonry meet the side of a house; joints between window frames and house siding; joints around large exterior beams; at building corners; where pipes or wires penetrate the ceiling or walls in attics; between porches or other additions and the main house; at roof edges, ridge caps, soffits, and fascia boards; where walls meet eaves at the gable ends of an attic; and in gaps under shingles.
- If you or a friend have bats roosting in their attic, avoid bat exclusion during the maternity season (May 15-August 15 in Maine), so flightless baby bats are not separated from their moms. There are one-way doors that allow bats to fly out but not get back in.
- Don't visit caves in winter (October 1-April 30)- this is the time of year that hibernating bats need to conserve all their energy. Any disturbance can cause bats to use up precious energy reserves and starve to death.
- Build or Buy a bat house when you exclude a bat colony from your house, but make sure to do your research first.
Living with Wildlife
How to Prevent or Resolve Conflicts with Bats
For some people bats don't present a problem. For others, bats can be a worry, especially when they become unwanted guests in an attic, inside a wall, or in living space.
Unlike rodents, bats have only small teeth for eating insects, so they do not gnaw holes in walls, shred material for nests, chew electrical wiring, or cause structural damage to buildings. Bats therefore cause minimal damage, but they can be noisy and alarming, and the smell of bats and their droppings can be offensive. It is possible to learn to coexist with bats and to benefit from their presence.