by Whit Gibbons

September 5, 2010

I have received the following questions about bats during the last few weeks.

Q. How many kinds of bats live in the United States? Do they only come out at night? I am sure I saw one last week before dark.

A. More than 35 different species of bats are found in the United States if several tropical species that enter some of the southwestern states are included. A half dozen U.S. species are widespread, ranging from coast to coast and from Canada to the Gulf States. And about half a dozen species have geographic ranges that are restricted to the United States, the vast majority being found also in Canada, Mexico, or both. Bats are able to be completely nocturnal by using supersonic sound production that allows them to find insect prey and avoid physical structures with echolocation. However, bats have tiny eyes and can see in the daytime; they are occasionally active an hour or so before dark and after sunrise.

Q. Is it true that a disease is driving the country's bats to extinction?

A. Conservation biologists are especially concerned about a type of fungus that can grow on the exposed skin of bats and cause death during hibernation. The disease is known as white-nose syndrome because the fungus is whitish and the nose of most bats is exposed and likely to be attacked. The origin of the fungus is unknown but has been found on bats in Europe. Some scientists believe it may have originated there and has now become an invasive species in North America. Because U.S. bats have not been exposed previously to the fungus and thus have evolved no natural immunity, white-nose syndrome has been devastating to bat colonies.

A study conducted by Boston University's Winifred F. Frick and other scientists ascertained the extent and potential impact of white-nose syndrome on selected species of U.S. bats. They used research data collected for 30 years on bat colonies at more than 20 hibernation sites, including caves and mine shafts as far south as West Virginia. The first discovery of white-nose syndrome in U.S. bats was in a New York cave five years ago. Since then the disease has spread like an epidemic, resulting in the deaths of more than a million bats in 14 eastern states, from Maine to Tennessee. More than nine bat species have been found to be susceptible to the invasive fungus, and projections are that the epidemic will spread to bat hibernation sites from the Carolinas to Alabama.

Frick and her colleagues focused part of their study on a particular species known as the little brown bat, or little brown myotis. Many people have seen little brown bats at one time or another as it is one of the most widespread and common bat species in the country, with more than 6 million individuals. They range from eastern Canada to Alaska to California to the Southeast. An estimate of flying insects, including mosquitoes, eaten by little brown bats in a year would certainly number in the millions and be measured in tons by weight.

The researchers have found that little brown bats are highly susceptible to white-nose syndrome and that the disease is present in more than 100 hibernation sites they examined. Unfortunately, they found that the mortality rate averaged more than 70% across the colonies and as high as 99% in some. The really bad news is their prediction that little brown bats regionally affected by the fungus will go extinct in only 16 years. The implications that similar responses might be seen in other species of bats and in other parts of the country are disquieting.

The findings about white-nose syndrome underscore how serious introduced, invasive diseases can be to native species that have no evolutionary experience with them. The fact that we could lose an important component of our natural ecosystems, especially one that eats so many mosquitoes, is not a pleasant one. Let's hope that further research will offer solutions for ways to control the spread and impact of the deadly fungus.

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