TOWNSEND'S BIG-EARED BAT
By Eileen Dowd Stukel
When I was a little girl, I was terrified to visit the large city park next door after dark. My brothers had convinced me that the bats flittering through the air would entangle themselves in my hair. After futile attempts to free themselves, the bats would have to be removed by chopping my hair off.
This ridiculous bat myth is still believed by many, along with other incredible myths and superstitions. Why are bats the objects of such fear and suspicion? A common characteristic of most human fears is a lack of understanding. Combine this ignorance with a bat's secretive and nocturnal ways, its unusual appearance and its association with Count Dracula, and you have a serious public relations challenge.
If we're willing to set aside our preconceptions about bats, we can quickly come to appreciate this remarkable group of mammals. There are approximately 1000 bat species worldwide, and they are very similar to bat fossils 50 million years old. Bats are grouped in the Order Chiroptera, which translates to "hand-wing". Bats are the only true flying mammals, with elongated hands and fingers to support wing membranes. Diversity among bat species is immense. Bat sizes range from the world's smallest mammal, the bumblebee bat of Thailand, weighing less than a penny, to the flying foxes, some with wingspans up to six feet.
I had a recent conversation with someone about endangered species. After each description of a few of the rarest species found in South Dakota, the individual would ask: "But what's it good for?" Answering this question about bats is simple. In both the New and Old World tropics, many economically important plants rely on bat species for pollination. These include bananas, avocados, dates, figs, peaches, cashews, carob, mangoes, and even the tequila plant, from which we derive mescal. The African baobab, commonly called the "tree of life", is bat-pollinated, one of over 300 tropical plants of Asia and Africa that depends on bats for pollination or seed dispersal.
On a more selfish note, North American bats truly are insect-catching machines. As the major predator of night-flying insects, bats consume enormous quantities of mosquitoes, as well as many agricultural insect pests, including grasshoppers, corn borers, potato beetles and grain and cutworm moths. One little brown bat, a common North American species, can catch 600 mosquitoes per hour.
Despite their tremendous economic and ecological values, many bat species have declined. The tiny bumblebee bat is an endangered species, as are seven bat species found in the United States. The Townsend's big-eared bat is considered a rare and vulnerable species in South Dakota. This species, sometimes called the lump-nosed or long-nosed bat, is found mainly in caves of western North America. Smaller populations are scattered through parts of the southern Great Plains, the Ozarks of Missouri, Arkansas and Oklahoma and portions of Virginia and West Virginia. Two subspecies, the Ozark big-eared bat and Virginia big-eared bat, are endangered. In South Dakota, this species has been found in caves and abandoned mine tunnels of seven western counties, in both nursery and hibernation colonies.
Female big-eared bats mate during October and November of their first year. Like most North American bats, this species exhibits delayed ovulation and fertilization. Not until the spring following fall mating is an egg released from the female's ovary, to unite with the sperm for fertilization. In the meantime, both sexes gather in caves and mines for hibernation, one of two winter options for an insect-eater. This species typically doesn't migrate for any great distance, but instead forms hibernation clusters of a few to several hundred bats in caves or mines with temperatures of 55 degrees F or less. Their sensitivity to temperature changes can cause them to shift to different sites within a cave or even to other caves during hibernation. Big-eared bats usually select the cool, well-ventilated parts of a cave, where they hang from an open ceiling.
Ovulation and fertilization occur usually just after bats have left their winter quarters. Pregnant females gather in nursery colonies, where they give birth to one young each, after a gestation period of 8-14 weeks. A big-eared bat is relatively large at birth, measuring one-quarter of its mother's size. During daytime roosting, young suckle and cling to their mothers. They are soon left in clusters as the females forage, leaving after dark in search of night-flying moths. A newborn can "chirp" a few hours after birth. It's possible that this vocalization may help a mother recognize her infant when she returns to the maternity roost.
Young big-eared bats grow rapidly, are flighted by three weeks of age and weaned at two months. By this time, usually late in the summer, nursery colonies disperse, to reform the following spring. Townsend's big-eared bats are extremely faithful to maternity roosts, returning annually if not disturbed or displaced.
This species is not considered common anywhere in its range, possibly due to its extreme sensitivity to disturbance. If disturbed in a maternity colony, pregnant females may abort or resorb an embryo. Mothers with young may drop their infants in panic or abandon helpless young at a maternity site. In any case, this can be a serious population loss for a species that gives birth to only one young per year.
Hibernating bats are likewise at great risk when disturbed, either accidentally or intentionally. Bats prepare for hibernation by adding fat that may amount to one-third of their body weight. This fat store is drastically depleted if a bat is aroused during hibernation. Each disruption can result in a bat losing up to 30 days worth of its winter fat storage.
What can you do to help this unique and sensitive element of our natural heritage?
1. Report any bat activity you see in South Dakota's caves or old mines. The Game, Fish and Parks Department, Black Hills National Forest and the Paha Sapa Grotto, a spelunking club, have embarked on an inventory of potential bat habitats in the Black Hills of South Dakota. Such information can help us identify and protect critical bat habitat for the eleven species found in the Black Hills.
2. Do not explore caves inhabited by bats. Human disturbance and persecution are two of the most serious threats to bats' survival. Unfortunately, many Black Hills caves aren't presently used by bats because of extensive human use, vandalism and soot build-up from campfires set inside caves.
3. Learn more about bats and their conservation by joining Bat Conservation International, a nonprofit organization dedicated to the worldwide conservation and management needs of bats. Membership information can be obtained by writing to:
Bat Conservation International
PO Box 162603
Austin, TX 78716