Bats of New Hampshire

Bat Biology 
 

Bats are the only mammals that engage in truly active flight (other mammals, such as "flying" squirrels, can only glide from tree to tree). They are generally nocturnal, sleeping during the day in sheltered areas called roosts and flying at dusk to forage for insects.

Bats eat insects, millions of them! These include a large number of agricultural and forest pests, as well as pesky mosquitoes. Bats can eat 50% of their own body weight each evening, and even more if they are females with pups. This is the combined weight of over 1,500 mosquitoes! A recent analysis of the value of pest control services provided by bats was at least $3.7 billion a year.

Bats use echolocation to navigate and to locate prey. As a bat flies, it sends out signals that bounce off of their prey and come back to the bat's sensitive hearing. Once the bat has pinpointed her prey in this way, she swoops in the direction of the signal that bounced back and catches the insect in her mouth, sometimes using her wings and tail membrane to help.

Bats use a variety of habitats throughout the year. In the summer they need foraging and roosting (resting) habitat. In the winter they must deal with deep cold and no insects for food. Five of our species hibernate to survive, and three migrate south to warmer areas for the winter.

Female bats often have their babies grouped together in a maternity colony. Males roost separately or in small groups in different roosts. They have very low reproductive rates, with females usually producing only one, but sometimes two pups per year. The young are able to fly in about a month, but still depend on the safety of the roost as they learn to forage on their own. Like all baby wild animals, not many make it to adulthood. Bats are long-lived animals, with a lifespan around 20 years in the wild.

In August, bats move out of their summer roosting sites and either fly back to their hibernacula, or migrate south. Bats fly and hunt together in September and October, storing food as body fat, which their bodies will use during the cold months ahead. Mating also occurs during this time, but the female stores the male's sperm in her body and fertilizes her egg in the spring ("delayed fertilization"). This way she saves her stored fat for herself to survive the winter, and is able to have a healthy pregnancy in the spring when insects are plentiful.   

Because there are fewer insects to be found in winter, and because it is so cold, some bats hibernate, from November through April in NH. To hibernate, bats lower their body temperature, metabolism, and breathing rate, and thus are immobile for long periods of time. It is critical that bats not be disturbed during this time, because whenever a bat "wakes up" (even temporarily) from hibernation, its metabolism increases, which uses up precious reserves of fat.

Natural predators of bats include owls when bats are flying at night and animals such as raccoons and ravens if they find bats roosting.

Bat Habitats in Summer

In the summer bats forage in woods, often using trails and wood roads. They follow stream corridors and fly over ponds and fields in search of insects.

During the day bats roost, with males generally separate from females. Different species of bats use different types of roosts. Five species mostly use trees, two use buildings and one roosts in rock crevices.

Tree-roosting bats use different parts of the tree – foliage, loose bark or cavities – and prefer different species and ages of trees to shelter under. Eastern red bats and silver-haired bats roost in taller, more mature trees, while Northern long-eared bats need older forests surrounding them. One strategy listed in the Wildlife Action Plan to protect these and other species is increasing the amount of late successional or old-growth forests. Since all the tree-roosting species, including the tricolored bat and hoary bat, seem to return to the same roosts summer after summer, the loss and fragmentation of the forests can severely diminish their populations by removing the all-important maternity roosts. None of these bats produces many young per year – most have only one or two but not all make it to maturity.

Eastern small-footed bats (state endangered) spend the summer in rock crevices, in rocky outcrops. Some human-made structures like dams and riprap slopes can provide habitat, but measures must be taken to avoid harming the bats during routine maintenance of those structures.

Little brown bats and big brown bats prefer buildings – barns, attics and other outbuildings – for their maternity colonies. The ability to crowd more bats in and the higher temperatures of these buildings allows for a more rapid growth of the pups. Bat houses can substitute for buildings, but must be large enough and put up properly. Get more information on bat houses on our homeowners page.

If you have a summer colony in your barn or attic, participate in our statewide summer bat survey.

Bat Habitats in Winter

Little and big brown bats, northern long-eared bats, eastern small-footed bats and tricolored bats all hibernate in caves and mines, and are generally called cave bats. The "hibernacula" have very stable temperatures between 40 and 50 degrees F and humidity over 80%. These conditions protect the bats from freezing or dehydrating in the long months of winter. There are not enough mines with the proper temperatures and humidity here in New Hampshire for all of our summer bats, so many fly out of state to hibernate in Vermont, Massachusetts or New York.

These temperatures and humidity ranges are also ideal for the fungus Pseudogymnoascus destructans, the causative agent of white-nose syndrome, a disease which has killed over 5.7 million bats. Read more information about white-nose syndrome.

Tricolored bats, little brown bats, federally-threatened Northern long-eared bats, and state-endangered Eastern small-footed bats hibernate in caves or mines. They are highly vulnerable during winter, surviving only on the fat they have stored in their bodies. Spelunkers – people who explore caves – may not even see the bats, but can easily disturb them with lights and noise. Even casual visitors to caves in the winter have a big impact, because the disturbance causes bats to arouse from hibernation, using up precious stored energy. Big brown bats hibernate in caves, mines or buildings. The bats in buildings may be protected from white-nose syndrome, but those in caves and mines do get the disease

Three species of bats migrate south: Eastern red bats, hoary bats and silver-haired bats. Like migrating birds, they are exposed to many obstacles during their migration. A new and emerging threat is the rotating blades of wind turbines on top of ridges, since bats and other migrating species follow rising air above ridgelines for flying ease.

Threats to Bats and How We Are Addressing Them

White-nose syndrome is a new disease that affects bats while they are hibernating in caves and mines. The disease is generally fatal to several species of hibernating bats, and several species have declined by nearly 99% in New Hampshire. Over 5.7 million bats have died prior to 2012 in the Northeast. White-nose syndrome is spreading south and west as well as up into Canada. Read more information about white-nose syndrome.

To help hibernating bats, stay out of caves and mines so as not to disturb fragile, hibernating bats. In places where caves and mines are closed, observe these cave closures. Please follow the caver advisories to avoid spreading white-nose syndrome.

Loss of foraging habitat, maternity colony structures, and roosting habitat in general are other threats to bats. Maintaining suitable foraging habitat near bat roosts and hibernacula is critical. Many insect prey live as juveniles in the water, so clean water is also important to bats. Buildings which are torn down or tightly sealed prevent use by bats. Homeowners and barn owners often do not like bats in their buildings, either because they dislike bats or have problems with the accumulation of guano. We do not know how long it takes bats who are excluded from traditional roosts to find a new roost or if exclusions affect bats' ability to raise pups.

Wind-energy facilities, whose turbines can either indirectly or directly kill large numbers of migrating bats, are one of the main threats to bats as they move to hibernacula or migrate. Turbines may actually be attractive to some bats, who are curious about this strange structure on the landscape. Bats die from being hit by blades and also by barotauma, where the changing air pressure caused by the moving blade actually causes the blood vessels in the bats to rupture. Bat deaths appear to be more common at low wind speeds, so stopping turbine blade rotation at slow wind speeds can save many bats.

New Hampshire Fish and Game helps to protect bats by monitoring the state's hibernating bats in winter, protecting bat hibernacula from human disturbance, encouraging bat-friendly and sustainable forestry, working with private landowners who have summer bat colonies, and advising on wind power facilities. Fish and Game is also teaming with federal and other state biologists to help bats recover.