3 August 1993. I'm perched high on a hillside overlooking the White River near Stockbridge, Vermont. About 20 other people are here with me, and together we are installing a steel grate at the mouth of an old abandoned talc mine. We come from many different groups: the Green Mountain National Forest, the Vermont Nature Conservancy, the Vermont Department of Fish and Wildlife, an autobody shop in Manchester, newspaper reporters, TV camera crews, and Middlebury College. It has taken our helicopter three trips to airlift the 600-pound grate, generator, rock drill, and welding equipment up to the mine. It will take almost five hours to build the grate, pour cement to form an even foundation, drill holes into the rock wall at the mouth of the mine, and weld the steel to rebar rods inserted deep into the rock.
The grate itself is small, only about four feet high by three feet wide, and is made of steel bars spaced about 12 inches apart. Part of the grate is a small gated section that can be locked into place, yet removed if necessary to allow a human to squeeze through and enter the mine.
Why are we doing this? This mine, the Greeley Talc Mine, is not itself particularly special. After producing talc for several years at the beginning of the century, it was abandoned and nearly forgotten. It runs only about 60 meters into the hillside, and boasts neither vertical shafts nor crumbling walls that would require it to be closed off to humans. It isn't a natural geological formation or a site of historical importance. Why all of this attention?
The answer is that this mine, like many others throughout North America, is the winter home of a large colony of bats. It hosts five different species of bats for up to eight months each year. Almost 1000 individuals have been counted here in mid-winter. Although that isn't large by standards of the past, it makes the mine one of the largest hibernacula in Vermont today. The grate we are installing is of a unique design that allows bats to fly freely through its bars, yet prevents humans from entering when the gate is locked.
Why should anyone do this for bats? What's the point of building and installing a grate that allows bats to live undisturbed, safe in a hole in the ground? Let's face it--bats rank right up there with snakes and spiders as the animals people most love to hate. Fortunately, a growing number of people are working to save bats. Herein lies a story of wildness, otherness, and the need for restoration.
Bats are mammals, like us, and one of only three vertebrate groups ever to have evolved the capacity for powered flight (the others being birds and the now extinct pterodactyls). Unlike birds, however, bats have wings made of skin stretched between the hind legs and up to elongated arm and finger bones. In all bats but the flying foxes, the primary way of getting information about the world is by means of echolocation, whereby bats detect objects as small as a tenth of a millimeter in diameter by hearing the echo caused when the sounds a bat makes in its larynx bounce off the object back to the bat's ears. By producing as many as 200 clicks per second, bats can build up a very complex image of the world, and this ability allows them to fly with great precision at night and in the blackness of caves. Although the night sky during the summer is filled with bats and a constant din of powerful clicks, we humans don't hear the sounds the bats make because they are up to 5 times higher in pitch than sounds our ears can detect. Nonetheless, the sounds emitted from each bat have a force comparable to that made by a jet flying close overhead.
An apocryphal story is told about the reaction Donald Griffin and Bob Galambos received when, in 1940, they presented to the scientific community their proof that bats use echolocation. Scientists who had recently developed sonar technology, which operates on principles similar to those of echolocation, were irate that Griffin and Galambos would suggest that bats had mastered this ability as well. They were somehow offended that their technological achievement had been foreshadowed 50 million years ago by animals that can weigh less than 10 grams and require no hardware or power supply.
Bats are found on every continent except Antarctica and on most oceanic islands. The only native mammal to the Hawaiian Islands, for example, is the hoary bat (Lasiurus cinereus), blown across the Pacific Ocean millennia ago by some far-reaching storm. With over 900 species, bats (Order Chiroptera) are second only to the rodents (Order Rodentia, with over 1700 species) in terms of numbers. Ecologically they are extremely diverse as well. In the tropics, for example, where the greatest diversity of bats is found, there are species that specialize in eating fish, fruit, insects, nectar, pollen, blood, lizards, rodents, and other bats. In many ways, bats are the nocturnal equivalents of birds, filling a suite of ecological roles vital to ecosystem function, such as pollinators, seed dispersers, and predators.
In central and northern North America, the ecological diversity of bats is less than that in the tropics, and all 40 or so species feed almost exclusively on insects, sometimes in phenomenal amounts. A single little brown bat (Myotis lucifugus) can eat up to 500 insects per hour. A colony of only 1000 bats can eat 8 tons of insects per year. During the warm summer and early fall months, bats congregate in areas where insects are plentiful--fields, streams, and forests--sleeping by day in trees, caves, and (nowadays) buildings and coming out as the light fades to capture insects and other invertebrates on the wing or ground.
In temperate North America, however, insects aren't available all year round, so most bats hibernate in winter, normally in caves and hollow trees, but also nowadays in abandoned mines and buildings. While in hibernation, their bodies enter a physiological state called torpor, where their metabolic rate drops 95% and their heart rate drops from 210 down to 20 beats per minute. Torpor does not mean turning the body off, however. They still burn energy, in the form of body fat that they deposited the summer before. Each bat carefully regulates its body temperature at 5o to 10oC (depending on the species), and is easily awakened if disturbed. They choose hibernation sites that minimize the amount of energy they must spend to keep their bodies at these temperatures. Caves that are too shallow or locations that are too close to the mouth of a cave tend to have air temperatures that drop below 0oC during the winter, forcing the bats to burn up precious fuel to keep from freezing. Deep in large caves, however, away from drafts, the air stays at a relatively constant temperature regardless of what is happening outside. The humidity also stays relatively constant and high, sometimes as much as 75%, which minimizes the amount of water bats lose from their lungs as they breathe.
Bats are thus highly complex animals, both ecologically and evolutionarily. They sense the world in a way we can barely imagine, and provide a constant reminder that reality is more than what we can sense by ourselves. They show adaptations that exceed our own technological developments, play critical roles in ecosystem function, and also, by virtue of their appetite for insects, make it easier for humans to produce our own food through agriculture.
Yet humans have pushed bats, as a group, into big trouble in temperate North America (and elsewhere). Assaulted by several factors, the numbers of almost every species on this continent have plummeted over the past 30 years. In one cave in southern Vermont, for example, the wintering population of little brown bats has dropped from over 300,000 in the 1960s to under 300 in 1992. In another, smaller Vermont cave, the population dropped from several hundred to 33 over the same period. In Missouri, the winter population of Indiana bats in one of the most important hibernation sites declined from almost 72,000 in 1960 to 33,000 in 1980. Several populations of Ozark big-eared bats in Arkansas have declined. The population in one cave dropped from 420 in 1980 to 240 just two years later. In another, the population dropped from 60 in 1975 to just 3 in 1982. And so it goes. Although only 6 of the bat species or subspecies in temperate North America are federally listed as Endangered (the gray bat [Myotis grisescens], Indiana bat [M. sodalis], Mexican long-nosed bat [Leptonycteris nivalis], Sanborn's long-nosed bat [L. sanborni], Ozark big-eared bat [Plecotus townsendii ingens], and Virginia big-eared bat [P. t. virginianus]), almost all of them have shown staggering declines in numbers.
The natural history of bats makes them particularly susceptible to being killed by human activity. Their first problem stems from their diet of insects. In our efforts to increase agricultural output on each hectare of farmland, we use pesticides to kill the insects that compete with us for this plant food. With each new type of insecticide or larger dose of a poison already in use, most of the insects are killed. Yet some small fraction of them have a genetically-determined resistance to the toxin, a resistance that is then passed on to the next generation. Soon the entire population possesses the resistance, and new insecticides or larger doses must be employed. Since insects can breed many times in a year, several generations of insects can pass in a short period of time, leading to rapid re-establishment of insect populations.
The story is familiar. Rachel Carson raised the alarm in 1962 about the destruction of healthy ecosystems by insecticides, but the problem continues today. Insecticides pose particular dangers for bats. Even though insects are resistant to many of the toxins we spray on our food plants, they still have those chemicals in their bodies from having eaten the plants. When a bat eats these insects, the toxins are incorporated into the bat's body. Here the toxins build up, insect by insect, to levels that can weaken, sicken, and eventually kill the bat. Because of generation times longer in bats than in insects, resistance never has a chance to spread through a population of bats before they experience new toxins and higher dosages.
The problem is especially acute in the winter. Many of the pesticides are soluble in the fat that bats deposit for hibernation. Then, as they metabolize the fat during the winter, the toxins are released into the blood in such high doses that the bats can eventually die.
We've begun a vicious cycle. To kill insects, we use pesticides, which kill the bats, which lead to more insects and the use of more pesticides. Rachel Carson's silent spring is rapidly becoming a silent night as well.
The second major problem for bats comes from their habit of congregating in caves and mines during hibernation. Here, clustered together by the hundreds and thousands, they are vulnerable to disturbance that can lead, either quickly or slowly, to death. Much of the disturbance is unintended. Caves and mines have often been walled closed for reasons of human safety or liability. Disturbance in the surrounding landscape, such as logging or construction, can alter the flow of air and water through the underground passageways, changing climate conditions in ways that destroy their suitability for hibernation. Bats are sometimes handled by curious spelunkers, which causes the bats to wake up and, in the process, burn up almost a week's worth of hibernation energy. If this happens often enough, the bats run out of body fat before spring arrives, and fall helplessly to the floor of the cave.
Some of the killing is deliberate. Prompted by a misplaced fear of rabies or just plain meanness, bats are killed en masse as they cluster together. Most caves and mines today bear the scars of shotgun blasts and blowtorches where bats once roosted.
Which brings me back to the grate on the mine in Stockbridge, Vermont. There's still much we don't know about bats: how long they normally live in the wild (the current record is 32 years!), the movement of individuals between summering and wintering grounds, how populations find new hibernation sites, and how the structure of a forest influences their survival. Yet we do know a few things we can act on, in particular that during winter they simply need to be left alone. Hence the grate and its locks.
None of us here believe for a minute that this alone will be enough. Bats aren't in trouble only because of vandalism and habitat disturbance. They are victims as well of non-point source poisoning. Any recovery plan for them must involve a general transformation in how modern humans feed themselves, and that's more than those of us up here today can solve on our own.
But still we drill and weld and pour cement. At least now this place will be safe for them, and that is a part of what must be done.
Everyone can contribute to the recovery of bats in several ways. First, speak out about their ecological importance and the need to protect them and their hibernation sites. Increasing the level of understanding and appreciation of bats is important in order to reduce their deaths due to fear and ignorance. Second, contact Bat Conservation International (P.O. Box 162603, Austin, Texas 78716-2603). This organization offers a wide range of written material designed to help educate the public about bats and promote bat recovery, such as designs for building bat houses. Finally, it is essential that we transform our current agricultural policy, which depends heavily on pesticides, into one that is integrated into natural ecosystems. Currently in North America, the greatest progress in this transformation comes from the field of sustainable agriculture. To learn more about the importance of sustainable agriculture in reducing our use of pesticides and how you can promote sound agricultural policies, contact the Institute for Agriculture and Trade Policy (1313 Fifth Street S.E., Suite 303, Minneapolis, Minnesota 55414-1546).