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Research scientists who have performed studies at Kentucky’s Mammoth Cave National Park have confirmed high levels of mercury in park bats. The endangered Indiana bat is now among the species which have dangerously-elevated mercury levels.

Experts from the park and Western Kentucky University conducted the research, which was intended to measure the amount of the poisonous metal in park wildlife, including bats that inhabit Mammoth Cave.

Their work is now also shedding light on how pollutants, such as mercury, become concentrated in and saturate our natural environment.


During the park study, teams of researchers spent two summers using nets to capture hundreds of the estimated 6,000 to 8,000 inhabiting bats for evaluation. The teams strategically placed the nets at locations the bats were expected to fly during the evening hours, such as at the mouth of caves.

Once researchers caught the bats, locks of hair were trimmed from the animals, placed in sterile bags and sent to a Western Kentucky University laboratory for evaluation. As is the case with human beings, the level of mercury found in the bats’ hair has been revealed to correlate with the amount of mercury in their small, fury bodies.

This correlation is called “biomagnification.” Biomagnification is the process where concentrations of a specified pollutant, in this case mercury, increase at each link in the food chain. Prior to this groundbreaking research, mercury studies typically focused on humans and other animals that consume mercury-tainted fish, which are just one step higher on the food chain than the lowly insects. As it turns out, the recent research on bats verses mercury pollution is quite revolutionary because it is revealing that biomagnification even takes place in animals that feed on tiny insects.

In the case of bats, toxic mercury, derived primarily from power plants, falls to the ground and accumulates in a multitude of microscopic plants. These plants are then eaten by minuscule animals, which are then eaten by insects, which are finally devoured by our only truly-flying mammal, bats. Through each of these eating cycles, the quantity of mercury increases until it reaches the bat. In other words, the bat accumulates more mercury than the insect, the insect has more than the minuscule animal, and the minuscule animal has more than the microscopic plant. And so it goes.

Environmental groups and park authorities are placing the blame for the increased mercury contamination primarily on the emissions from Kentucky’s many coal-fired power plants. Utility companies, however, say they are reducing mercury emissions as a result of recent legislation. They point out that some mercury in the atmosphere comes from certain natural events, such as forest fires and volcanoes.

Additionally, Kentucky’s coal-fired power plants are likely not the only mercury contributor as bats do migrate and can acquire the lethal mercury during their travels to neighboring states. Mercury, like bats, is also able to travel long distances before settling in bodies of water or being soaked up by tiny plants.

While Kentucky’s power plants are not the lone mercury bandit, many environmentalists call Kentucky a mercury “hot spot” due to the sheer number of coal-fired plants. In fact, state officials have had to issue mercury warnings cautioning people against eating fish taken out of rivers, creeks, lakes and ponds located in all 120 Kentucky counties.

Although it is yet to be determined whether or not the amount of mercury found in these bats is actually causing serious harm, such as damage to the central nervous and reproductive systems, researchers have already found mercury in the bats’ hair at nearly 10 parts per million.

10 parts per million is an extremely elevated level, a concentration beyond which detrimental health effects are detected in humans and a variety of rodents. In fact, the United States Environmental Protection Agency reports that human mercury exposure should be limited to 1 part per million. This is a whopping 10 times lower than the level found in bats during the Mammoth Cave National Park study.

It is now understood that bats are especially susceptible to the toxic metal due to their high metabolic rate, which requires the bats to consume an excessive amount of insects every night. In fact, bats are better than your average bug zapper light as many can easily eat close to their body weight in insects in just one night. That’s a lot of bugs.

Because of the sheer number of insects bats must eat to survive, it is believed that mercury has the obvious potential to seriously affect a bat’s ability to reproduce, thus hindering their capability of keeping their species alive. Mercury contamination can also alter the way the baby bats’ brains develop as well as impair the adult bats’ ability to care for their new babies.

For the furry-faced Indiana bat, which is found throughout the eastern states, the future is uncertain as they are still facing the threat of extinction. At one time, this tiny flying mammal, only weighing as much as three pennies, is estimated to have numbered up into the tens of millions in and around Kentucky’s Mammoth Cave National Park.

Urban development, increased farming and deadly tree diseases depleted and, in fact, removed a significant amount of these tiny bats’ maternity habitat and food supply. Prior to 1941, when Mammoth Cave was designated as a national park, much of its 52,000-plus acres were used as cattle grazing-ground, farmland as well as a prime location to harvest a great deal of timber.

Dutch elm disease also eliminated 90 percent of the nation’s American elm trees; a member of the elm tree family that the Indiana bats used to raise their young. Currently the Dutch elm tree has made a comeback, however the current woodlands are still too young to support the needs of the many roosting females. This serious decline in suitable roosting trees presents quite a challenge for mammals that only produce one offspring each year.

Scientists have estimated that, at one point in history, as many as ten million bats wintered in Mammoth Cave. That number has been reduced to zero. When the Indiana bat was added to the Federal Endangered Species List in 1967, their numbers had declined drastically; by greater than 60 percent. It is now estimated that the current national population of this bat is only roughly 330,000.

The Mammoth Cave National Park research findings, which are still being scrutinized, will most likely turn into a conflict between environmentalists, Kentucky power plants and, of course, government environmental authorities over the effects that toxic mercury emissions from coal-fired power plants has on the environment, including the bats who reside at the park.

In 2005, Environmental Protection Agency authorities imposed a seemingly significant limit on mercury emissions from power plants. These new regulations should reduce mercury emissions by approximately 70 percent over the next 13 years.

Many environmentalists, however, are still not convinced that these new mercury pollution regulations will be enough to protect the environment. Some groups have even challenged the new policy in court saying it is still too weak and will take too long to make a significant environmental difference.

While some may not give the future of creatures that often provoke fear because of their Halloween-like, spooky reputation of sucking human blood and attacking unsuspecting people, the importance of bats should not be underestimated.

Insect control, particularly of the dreaded mosquito, is just one of the benefits offered to the world by the bat. Consider the little brown bat that can swallow approximately 600 mosquitoes an hour.

The mosquito is just one insect different varieties of bats love to devour. The big brown bat can devour about 18 million rootworms every year, while the long-eared pallid bat can actually hear its prey – various walking insects, such as scorpions, centipedes and grasshoppers.

Not all bats eat insects, but they still provide other benefits to humans and our environment. Some bats, like the lesser long-nosed bat, drink nectar. Just like bees and hummingbirds, they carry pollen from one flower to another, thus aiding in the pollination of plants.

Photo:Doug Bowman

Some bats, like the short-tailed fruit bat, eat delicious fruit and scatter the seeds as they fly. Some 60,000 seeds can be distributed in one night by a single short-tailed fruit bat living in South and Central American rain forests.

Finally, take a minute to think of the mysterious vampire bat of Central and South America. While these bats do suck the blood of certain larger mammals, they pose no threat to humans. In fact, vampire bats have actually helped the medical profession.

Photo:bubblemonkey

Vampire bat saliva is unique and is made up of three ingredients that keep their preys’ blood freely flowing. An anticoagulant is the primarily component and works to keep the blood from clotting. A relatively new drug, Draculin, has been developed as a result of research and testing on the anticoagulant element of vampire bat saliva. This drug is now used to the benefit of human patients with heart ailments.

It should be obvious that there really is much to be lost if the diverse environments of the many bat species are not protected.

High Resolution Images from this article