Summer evenings give opportunities for a lot of outdoor enjoyment. One free and natural treat of the twilight hours is observing the world's only flying mammals, the bats. Using echolocation they are adept at avoiding all obstacles and honing in on the object of their pursuit -- their insect meal. (Don't worry about them flying into your hair.)

These amazing creatures comprise 20 percent of all mammals in the world, and nine species are known to live in Massachusetts. From those numbers you'd think we'd have a lot of bats, but many species are endangered, in decline or being watched carefully to monitor their health. It's time to overcome the fears and myths instilled in us by too many horror movies and folk tales that demonize bats, because they need our help, and we need them.

As consumers of insects, northern bats must either migrate or hibernate to survive our bug-free winters. Some of the ones that hibernate have been experiencing a rapid population decline caused by white-nose syndrome. Within caves, mines and other hibernacula, a cold-loving, non-native fungus develops on the nose, wings and tail membrane of infected bats. It causes them to wake up during hibernation, use up stored energy too fast and usually die of starvation.

Between 2006, when it was first identified, and 2011, white-nose syndrome killed more than 5.7 million bats in Eastern North America. Little Brown Bats were formerly the most abundant bat in the state. Most of their colonies are now gone.


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A decline in bat populations is something to be concerned about. Bats provide an amazing service to humans, other animals and plants. A nursing female bat can consume the equivalent of her own body weight in food in one night. An average-sized bat may eat 1,000 insects in an hour. When multiplied by all of the bats that could be hunting, that's a lot of bugs! In fact, bats are the greatest predators of night flying insects, including beetles, moths and mosquitoes. Some of these insects are detrimental to agriculture, forests and are vectors of disease. We owe a debt of gratitude to bats and will all pay a price if their numbers continue to drop.

In addition to disease, habitat loss and human impact, one element of bat biology that contributes to their falling numbers is their low birth rate. Rebounding from a loss is difficult, because females only give birth to one pup per year. Some species can live up to 25 years, but this is becoming less common with all of the assaults on their health and homes.

When it comes to homes, some species of bats share human-made structures. Attics and eaves of barns provide good roosting sites and plenty of heat in the summer when the babies are growing. Heat from the space and fellow bats enables the pups to convert more of their food energy into growth since less is needed to keep them warm. Adult bats may also choose these places for hibernation.

This overlap of building use sometimes causes conflicts with people, but it doesn't have to. Setting up a dropped ceiling or barrier between the bats and the floor is a way to collect the droppings which can then be used as rich and effective garden fertilizer. A form of internal "bat house" can also be installed to encourage the bats to congregate in a particular place that is less disruptive to human activities. If they are truly a problem, professionals can exclude bats from a building, but this should never be done from mid-May to mid-August when there may be young in the colony.

Large bat houses, placed on the south side of a building can provide a reasonable alternative for local colonies.

Even if you don't want to invite bats into your home or yard, consider the advantages of sharing space with them. They very rarely have rabies, are actually quite shy and prefer to be left alone. A few bats in the attic or barn is a small price to pay for non-toxic insect control and summer evening entertainment.