Despite their positive value, bats are among the most misunderstood, feared and persecuted mammals on Earth. Fostered by myths, horror films and exaggerated or erroneous news accounts, misinformed or malicious people have blown up, bulldozed shut or poisoned thousands of bat colonies worldwide. Millions of bats -- along with entire cave ecosystems -- have been lost.
In addition, untold thousands of bats have been killed by cave explorers. Hibernating bats must ration their limited fat reserves through the winter to survive until spring and then arouse. Human disturbance of a hibernaculum during this critical period often awakens bats, causing them to waste 10 to 30 days' supply of stored energy, reducing or eliminating their chance of arousal. During birth, young bats may be dropped or abandoned by their mothers when caves are disturbed by spelunkers.
Deliberate vandalism also has taken a toll. In recent decades, tens of thousands of bats have been intentionally killed in the U.S. alone. At Carter Cave State Park, Ky., three boys rampaged through a colony, destroying an estimated 10,000 Indiana bats.
Agricultural pesticides have had a serious impact on bat populations worldwide, especially on insectivorous species. Some 130 million Brazilian free-tailed bats ranged over the farmlands of southwestern U.S. and adjacent Mexico as recently as the early 1960s, consuming an estimated 250,000 tons of insects each year. But their very appetite for insects, now contaminated with persistent pesticides, caused a drastic decline in populations, perhaps 99 percent in some places.
Carlsbad Caverns in New Mexico is a good example. A population of Brazilian free-tailed bats estimated at 8.7 million in 1936 plummeted to just 250,000 by 1973. Studies showed high concentrations of DDE (a chemical formed by the breakdown of DDT) in many of these bats. DDT was banned for agricultural use in the U.S. in 1972. Since then, the population of free-tailed bats at Carlsbad has fluctuated between 250,000 and 3 million, far below pre-pesticide days. Fortunately, analysis in 1980 of guano from the free-tailed bat colony on Colorado's San Luis Valley revealed safe levels of pesticide residues. However, the animals may winter in Mexico, where DDT still is used.
Currently, five bats species are on the list of endangered species under the federal Endangered Species Act: the gray bat, Indiana bat, Virginia big-eared bat, and Ozark big-eared bat (all cave-roosting species) and the Hawaiian hoary bat, the only land mammal native to Hawaii. An additional nine species have been recommended as candidates for listing and need further study. Each of these species has reached its perilous state through direct or indirect human impact. The gray bat once was one of the most abundant mammals in the Southeast, ranging from the Appalachians to Oklahoma and from Indiana to Florida. A single cave in Alabama sheltered up to a half million of the animals. Vandalism and disturbance have led to massive declines. Today there are only about 300,000 of the animals’ left, and 95 percent of the species hibernates in just nine different caves. The Indiana bat has experienced a similar fate. Today only about a half million of the animals survive. Direct disturbance and vandalism have taken their toll, and foraging and nursery habitats have been destroyed.
Because of their colonial behavior, bats are more vulnerable to some natural disasters than other mammals. At Mammoth Cave National Park, Kentucky, the bones of approximately 300,000 bats were discovered several decades ago, testimony to a massive flood that occurred in 1937.