Nov/Dec 2014For Wildlife Watchers: Big Brown Batby Rob Simbeck, photo by Phillip Jones
Sometimes bats catch insects in their mouths. More often, they catch them with their tail membranes, which act as a scoop or net.
All living things are ultimately interconnected. There is no branch of life - no family or order of species - whose demise should not give us pause for concern. But seldom is the magnitude of that interconnection, and its potential cost to humans, as large as it is in the case of the order Chiroptera - the bats. In an expanding area of North America, several bat species are experiencing population crashes because of white-nose syndrome (WNS), a disease named for the white fungal growth it produces around the muzzles and wings of hibernating bats.
Bats play a critical role in agriculture and the production of our food supply. The key is their unbelievable nightly consumption of insects during growing seasons, including many serious agricultural pests - not to mention those that, like mosquitoes, carry disease and otherwise plague humans. A bat can eat a third of its weight in insects a night. It's estimated that a thousand bats will consume 8,000 pounds of insects a year, and a recent study published in the journal Science suggests that replacing that natural pest control would cost farmers $3 billion a year.
With the death toll for bats now estimated at six million, the situation is grave. In Pennsylvania, counts of wintering big brown bats have fallen by more than 70 percent. Other bat species have been hit even harder.
Big Brown Bat - Eptesicus fuscus
Description: Length, four to five inches; wingspan, up to twelve inches; weight, up to one ounce; color, light brown fur with dark brown to black ears, wings and tail membranes.
Range and Habitat: Mid-Canada through Central America. Varied habitats where flying insects are plentiful. Common throughout South Carolina.
Mating: Mate in fall. Female can store sperm for spring and after a gestation of approximately sixty days will deliver a live birth of one or two pups.
Viewing Tips: Bats emerge at dusk and are often spotted overhead about thirty minutes after sunset.
"We are facing the potential extinction of species from this disease," says Jeremy Coleman, national WNS coordinator for the U.S. Fish and Wildlife Service.
And while the impact of WNS in South Carolina is less dramatic, the disease is here and spreading. The presence of WNS was first confirmed in South Carolina in March 2013, making us the twenty-first state to report it, although it has thus far been identified only in Pickens, Oconee and Richland counties.
"We are already seeing a decline in the tri-colored bat," says Mary Bunch, a biologist with the S.C. Department of Natural Resources. "Nobody should assume that they are WNS-free just because it hasn't been confirmed in their county. It is probably just a matter of time and detection before more counties are added."
WNS is caused by a "cold-loving" fungus that flourishes in the cool, dank caves and mines favored by some bat species. It is native to Europe, and its arrival on our shores - it was first recognized in New York in 2006 - has been devastating. The fungus affects the muzzle, ears and wings, imparting a fuzzy white appearance while dehydrating the bat, which wakes and flies off to seek water, often in frigid temperatures, using up its fat reserves and dying of starvation and dehydration. There is no known treatment or cure.
These are some of nature's most remarkable creatures. The only flying mammals, bats are found worldwide. There are about 1,100 species, three-quarters of them insectivores and the rest frugivores (fruit-eaters), except for three species in Central and South America that feed on blood. The big brown bat is one of the larger of the fourteen species found in South Carolina. Its fur is glossy, long and colored light brown, with its face, feet, ears and wings normally dark brown to black. Found throughout the state, big browns roost during the day in and around barns, outbuildings and attics, as well as in tree cavities and bark crevices. At sundown, like other bats they emerge from those roosts to hunt.
Sometimes bats catch insects in their mouths. More often, they catch them with their tail membranes, which act as a scoop or net. Their defecation, called guano, contains a great deal of nitrogen, phosphate and potassium, and has been used in fertilizer and even gunpowder. Their erratic flight is the result of hairpin turns to grab those insects. Moths are a staple of bats' diet, as well as beetles, flies and mosquitoes. Big browns "are so tough they'll even eat wasps," says Bunch.
The echolocation they use to map the area in which they're flying and locate prey involves a steady stream of sound that, though inaudible to us, is produced in some species at a staggering 130 decibels - that's more than a chainsaw or a "Who" concert. Others have calls that are nearly undetectable, even with audio equipment. That nightly consumption of insects feeds a highly revved-up metabolism - a bat's resting heart rate of more than three-hundred beats per minute can rise to a thousand when flying. Even so, says Bunch, "They spend a fair amount of time resting and grooming in between foraging."
A bat's wing structure is much more flexible than that of a bird. Their wings evolved from hand-like bones, and their muscles allow them to move the wing like a hand, as opposed to a bird's wing, which moves as a unit. They have oil glands, as birds do, to groom their wings, which are richly supplied with blood vessels, so they tend to heal quickly if scratched or torn.
Like many bats, those found in South Carolina hibernate during winter, often gathering in caves, mines, tunnels or the like. They enter an extended state of torpor, with their heart rates dropping as low as the teens, sometimes re-emerging for brief periods during winter warm spells.
"It is not well documented where the majority of big brown bats overwinter," says Bunch, "but buildings and trees are most likely."
They mate in the fall, and females can store males' sperm over the winter and activate gestation in the spring. They roost in maternity colonies when pregnant. Females give birth to one or two pups in June or July, while hanging from a hooked "thumb" at a roosting site. The young are naked and helpless and weigh a tenth of an ounce. They develop fur after about a week, nursing until they are capable of flight at six to eight weeks. The mother will leave them at the roost site as she feeds.
Bats carry a number of diseases, including, most famously, rabies, although only about one-half of one percent of bats is infected with the virus.
Bat predators include owls, snakes and kestrels, but humans are a major threat. People have long disturbed or purposely killed bats. State and federal agencies are working to protect bats by limiting access to caves used by bats and minimize the accidental spread of WNS.
As wildlife watchers, we can help by putting up good-quality bat boxes, especially in developed areas with few natural roosts, and by making sure not to disturb roosting bats in natural locations and tolerating them when possible in and around outbuildings and abandoned structures. A fascinating and essential part of our landscape, they are well worth protecting.