Monday, January 28, 2013

Hibernating Bats

In autumn, bats will find their traditional hibernation locations and often migrate hundreds of miles to the abandoned mines and caves where they will spend the winter months.

Some of our common New Jersey bats congregate in colonies, often in caves, mine or buildings. These "social bats" usually return to the same roost year after year and start maternity colonies in the spring.

Nine species of bats are considered regular residents of New Jersey. These include the little brown bat, big brown bat, northern long-eared bat, small-footed myotis, Eastern pipistrel, Indiana bat (state and federally endangered), hoary bat, red bat and silver-haired bat. The hoary, red and silver-haired bats are part-time residents that are found here from spring through fall. They migrate to southern states for the winter. The other six species remain here throughout the entire year and require special habitats for winter hibernation.

Natural caves once provided hibernating habitat for bats, but today most caves are subject to disturbance by people and thus are not suitable for use by bats. Abandoned mines and tunnels, storm drains and sewers have replaced natural caves as the primary winter habitat for many bats. Since those places are often unsafe to enter or inaccessible to people, they are desirable locations. But bats will sometimes hibernate in homes, garages, sheds and barns if there is access and it appears isolated to them.

New Jersey's largest known bat hibernaculum is the Hibernia Mine in Rockaway Township, Morris County. It was abandoned as a mine in the early 1900s and there are records of bats using the mine going back to the 1930s. After decades of the bats being disturbed, chased or even killed and landowner attempts to seal the mine, it is now a protected location.

Since they are particularly vulnerable to pollution and pesticides, the presence or absence of bats can tell scientists a lot about the overall health of the local environment.

Hibernating hoary bat on garage in Hunterdon County

I recently received via this site an email from someone in Hunterdon County who had discovered a bat hibernating attached to the outside of their garage. They were concerned about its exposure to the weather.

I recommended that they leave it alone and use the contact page at in the hope that they could give them advice or take the bat.

I'm pleased that this bat was picked up by Jackie of NJ Bats and she was very excited that it was a female hoary bat and was most likely pregnant.

Hoary Bat - Photo by Jennifer Linehan - 
Hoary bats are the most widespread of all bats in the United States and are thought to occur in all 50 states. They range from the tree limit in Canada down to at least Guatemala in Central America, and throughout South America. They are the only bats found in Hawaii.

They are rarer in most of the eastern United States but have also been found in Michigan, New York and Connecticut during December and in Indiana during January. This suggests that some may winter farther north than was previously expected.

Hoary bats are migratory and move north in spring and south in winter. It tends to be rather solitary and frequents wooded areas where it roosts in the open (not in buildings) by hanging from a branch or twig. It is more easily recognized by its large size and its swift, erratic flight. This bat usually emerges rather late in the evening, but during migration it frequently is observed in daylight hours

Two kinds of bats in New Jersey are often found roosting in colonies inside buildings: the big brown and little brown bats.

The big brown bat has a wingspread of about 14 inches and is our most common species. Colonies of up to 200 individuals return each spring to locations (including homes and other buildings) in New Jersey.

Although they have relatively long lives, reproduction is slow. Generally one is born each year. The big brown bat accounts for over 75 percent of the bat contacts with people and pets and is the bat most often tested for rabies.

Little Brown Bat
The little brown bat is also quite common in homes during the spring and summer, and large numbers hibernate in our abandoned iron mines. However, the number of human and animal exposures, and the number of little brown bats found to be rabid, are much less than for the big brown bat.

When bats are hibernating, it is a time that scientists often study them. Much of the research and surveying on White Nose Syndrome is done at this time.

White Nose Syndrome is a "bat plague" that has killed nearly 7 million bats since it first appeared in the US in New York State. The deadly fungal disease has spread to 19 states as far west as Missouri, as far south as Alabama and north into Canada.

The little brown bat (Myotis lucifugus) has been hardest hit by the sickness because it is the most common of our bat species, but there are 22 other species of American bats that also hibernate in caves that are being affected.

Bats showing the White Nose Syndrome fungus in hibernation

Like a number of other threatened and endangered species, such as snakes, wolves, and wood rats,  there are many myths and misunderstandings about bats.

For example, all of the bats found in New Jersey are strictly insect eaters. No vampires in Jersey. Many people fear a bat bite because of rabies. It makes sense not to touch bats that you find, but less than one percent of bats carry rabies and attacks by bats are extremely rare. They almost never get tangled in people's hair, despite my mother's warnings about that.

They are not blind, but they depend more on their sonar hearing than eyesight to navigate and avoid obstacles - and to capture insects. Because a bat can consume hundreds of insects in an hour, they keep our mosquito population down in areas where they congregate.

Bats are the only truly flying mammals. They belong to the order Chiroptera and are not rodents. They are mammals because the have hair, giving birth to live young, and feed their young milk produced by mammary glands.

Most bats produce only one offspring (called a pup) annually and rear their young for the first few weeks of life until they are able to fly and feed on their own. These reproductive and rearing practices make them the slowest reproducing mammals on earth for their size. Despite their slow reproduction, bats exist in large numbers and encompass one quarter of all mammal species, second in population only to rodents.

Individual bats can live to be 30 years old and colonies can be present at the same location for over 100 years.

A story last year on the Wild New Jersey site, says that while bat populations are on the decline across New Jersey and the United States, in Central New Jersey's Dismal Swamp Conservation Area (DSCA), the Edison Wetlands Association (EWA) and Eagle Scouts have taken action and are doing something about this world-wide bat extinction crisis. Bat populations in Northern Central New Jersey are actually increasing due to conservation activities.



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