Earth & Sky

Thanks to:

Lisa M. Nutt
District Wildlife Biologist
Clinch Ranger District
George Washington and Jefferson National Forest
U.S. Forest Service

Links:

To learn more about these fascinating creatures, visit the Bat Conservation International website here.

To learn more about the Clinch Ranger District (George Washington and Jefferson National Forest) and what they’re doing to conserve bats, please see the following links:

Forest Service Works to Protect Bats Living in Area Appalachian – Focus Environmental News, 8/2/00

U.S. Fish and Wildlife Service biological opinion on conservation efforts to protect Indiana bats at the George Washington and Jefferson National Forest

Former Home of More than a Million Endangered Indiana Bats Protected (Bat Conservation International)

Bat Workshops: Putting Conservation Into Practice (Bat Conservation International)

General Information about George Washington and Jefferson National Forest

General Information about the Clinch Ranger District

MORE INFO

Background information about bats:

There are many unfounded myths about bats. They are commonly regarded as symbols of evil in Western culture, associated with evil witches, ghosts, and even Count Dracula! These unfortunate associations have made bats feared by many people. But why? Perhaps bats’ bad reputations are a product of human ignorance, our fear of darkness and the unknown. After all, bats are mainly nocturnal creatures that lead mysterious lives. But people who have had a chance to get to know bats paint a very different picture of these animals. Bats, they say, are gentle, graceful, intelligent, and fascinating creatures that deserve our respect and protection.

Bats have been on the planet a long time, appearing in the fossil record as far as 50 million years ago. Worldwide, there are 900 species of bats, found mostly in the tropics. They range from tiny creatures weighing 0.07 ounces to large fruit bats weighing about 3 pounds. About 70% of all bats are insect-eaters. Some bats consume fruit, playing an important role in seed dispersal. Other bat species eat nectar and pollen, and are major pollinators of flowering plants. A few bat species feed on animal flesh. Perhaps the bats with the most notoriety are the Vampire bats of South America, they feed exclusively on blood.

In the U.S., there are 45 species of bats. Most are insectivorous and quite small, ranging in weight from 0.11 ounces to 2.5 ounces, depending on the species. Bats are mammals, warm-blooded and furry. And they have the distinction of being the only mammal group that can fly, exhibiting exceptional maneuverability in the air. (Note: Flying squirrels don’t fly, they glide from tree to tree, using membranes connected to their feet that extend along their sides.) Female bats give birth to their young and nurse them with milk secreted from mammary glands. In the U.S. and Canada, most bat species mate in the fall. The females store the sperm over the winter, and come spring, fertilization occurs. After a brief gestation period of a few weeks, the young are born. Most species typically bear one offspring each year. The babies develop quickly, and are able to fly on their own only 2 to 5 weeks after birth. Cave-dwelling bats form large maternal colonies in the summer to raise their offspring.

Bats have relatively good eyesight. But when hunting at night, they use echolocation to find their prey and to avoid obstacles. This sonar technique is done by emitting pulses of high-frequency sound that cannot be heard by human ears. These pulses are sent out anywhere from a few times per second to 200 times per second. When the sound pulses hit an object, it is reflected back to the bat, allowing it to “see” the object in front of it in complete darkness, be it an obstacle like a tree or building, or a flying insect.

Echolocation allows bats to catch their prey on the wing. A bat foraging on a warm summer night can eat as much as half its body weight in insects. Nursing females can eat their entire body weight in insects, also in a single night. This form of natural insect control makes bats a very important part of the ecosystem. In Chattanooga, Tennessee, for instance, a colony of 200,000 Gray bats that spend the summer in a nearby cave eat 440,000 pounds of insects each season.

In the U.S., most cave bats hibernate in caves or abandoned mines during the winter. In the summer, they roost in trees and buildings. Some cave bats also roost in caves year-round, using different caves for winter, summer, spring and fall. Man-made structures such as bridges are also popular homes for bats. In Austin, Texas, for example, 600,000 Mexican Freetail bats live during the summer under the Congress Avenue Bridge that crosses the Colorado River. The spectacle of large groups of bats leaving the bridge at dusk to forage has become a popular tourist attraction. Measures have been taken to protect bats living in caves and abandoned mines, by installing specially-designed steel gates at the cave or mine openings. These gates allow the movement of air through the cave or mine, and has openings that are big enough for bats to enter but prevents humans and other large animals from entering.

Some bat species roost in trees during the warm season, and hibernate through the winter in tree hollows, even in the leaf litter on the forest floor. Some species have wintering caves, maternity colonies in summer caves, and transitory caves in fall and spring. A few species migrate fairly long distances to summer and winter habitats. The Mexican Freetail bat, for instance, summers in the Southwestern United States, but winters 800 miles away in Mexico.

Hibernation is a state of torpor that bats enter during the onset of cold weather. Their metabolic rate decreases significantly: body temperature drops from 100 degrees Fahrenheit to about 40 to 60 degrees Fahrenheit. The heart rate also slows, from 100 beats per minute for a flying bat, to once every few seconds for a hibernating bat. During their winter slumber, the bats sleep in dense colonies, surviving on fat reserves accumulated during the summer and fall. When they wake up in spring, they would have used up about one-quarter to one-half of their body weight in fat during hibernation. It’s very important to not disturb bats during their winter’s rest. If disturbed, they burn up critically-needed fat reserves when responding to disturbance, and can emerge in spring in a weakened condition, resulting in poor reproductive success or mortality.

One common myth about bats is that they all carry rabies. Not true. Bats are just as likely to be rabies carries as other wild animals like racoons, foxes, and squirrels. When dealing with bats, just use the same common-sense precautions you would take with any other wild animal – admire them from a distance. However, if you see a bat on the ground, it usually means that the animal is sick, so don’t try to handle it. If you have unwanted bat visitors in your house, visit the Bat Conservation International webpage for tips on how to humanely and gently coax them out. Or call them at (512) 327-9721.

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Interview with Lisa Nutt, a wildlife biologist at the Clinch Ranger District at the George Washington and Jefferson National Forests. She has a special interest in bats, and has put a lot of effort into studying and conserving them.

Transcript:

E&S: Can you tell us about the kinds of bats you have in the area?

Ms. Nutt: We have a whole variety of forest bats. There are a number of bats in Eastern forests, and we have almost all of them in this area … we’re in the Mid-Atlantic area here. The ranger district is in the northernmost range of some southern species, and the southernmost range of some northern species, so we have a good variety of everything, including bats.

We have forest-dwelling bats, bats that use the forest year-round like Eastern Red bats. They have reddish fur, so when they’re up in the foliage in the tree, they’re camouflaged because they appear to be like dead leaves. They bear their young in the trees, and roost up there all summer long, and in the fall and winter, rather than going to caves or mines or buildings, like other bat species do, the Red bats actually hibernate in the forest floor. They’ll go underneath the leaf litter on the forest floor. In the winter months, if we get some really nice warm weather and warm evenings, there’s some insect activity and the bats will come out occasionally to forage. So you may see a bat in the winter. It’s unusual but it might be the Red bat. And they’re all fur so it helps them stay warm throughout the winter months.

We have other forest bats out there. We have bats that are forest dwellers in the summer, and cave-dwellers in the wintertime. And the one you hear about the most in the Eastern United States is the Indiana Bat, because it’s an endangered species. In the summer months they use tree roosts. Usually, they’ll roost under the bark of trees, bark that’s peeling, what we call exfoliating bark. Shag bark hickory is a tree species that naturally has fluffing or exfoliating bark. The bats roost underneath that bark. It’s really neat to see pictures of them up underneath the bark. And so the females form maternity colonies under there, and the males have bachelor roost trees that they use.

In the Midwest, they’ve done a lot of work with female Indiana bats and they know they’re using bottomland forests along riparian areas, along streams and river corridors. But then, in the Midwest, if you think about it, all the uplands are agricultural so the forest is found along the riparian areas. Here further east, we have a lot more extensive forest land and so they’re using a variety of habitats. We’ve not had a lot of success with capturing enough females to radiotrack them, to find out where they’re going and roosting.

The Indiana bats and some other bats dwell in caves or mines during the winter. They’re very vulnerable to disturbance, either inadvertent or intentional disturbance, in the the winter months. They enter the caves in the fall, having built up their fat reserves. Different species require different constant temperatures in winter. Some like it very cold, some like it a bit warmer. They’ll select the area of the cave or mine that provides that temperature and they’ll go into a torpor to hibernation, and live off those fat reserves during the winter months while they’re sleeping.

Unfortunately, when people come in and rouse them, the energy that’s lost in waking up and possibly flying around to get away from whomever’s disturbing them, those energy reserves needed to keep them going through those winter months are used. The problem can be that they either burn up so much reserves that they come out in the spring in very poor shape, during a period when they have to find insects, and insects sources are less reliable initially in the spring. That could cause low reproductive success or mortality. Or they could actually die during the winter months if they’re disturbed and burn up a lot of fat, although I don’t hear much about that. Mostly, it puts them in poor condition so when they emerge come spring time, they’re just not in as good a shape as they need to be to get to their location for the summer, and if they’re females, to be reproductively successful.

How we protect these bats in these caves and mines – and mines are dangerous anyway for humans to go into – is with bat gates. [The gates are] made out of angle-iron steel, that is steel in a 90 degree angle. The [gate] bars are 4 by 4 inch thick angle iron steel. The horizontal bars are spaced about 5 and 3/4 inches apart. Caves usually breathe in and out. The gate does not inhibit airflow movement, it allows air to continue passing unobstructed through the cave opening. But the opening in-between those horizontal bars is too small for people to get through. It allows the bats to easily pass through and keeps the temperatures within the caves prior to what they were before the gates were installed.

In the past, people were trying to protect bats [with gates] and keep people from disturbing them during critical time periods, like the months they were hibernating or for some bats that summer in caves and have breeding colonies. Inadvertently, they had designed gates that obstructed airflow and would change the internal cave temperature, causing it to be unsuitable. So this [newer] design is used throughout the country, probably throughout the world, and has been real successful.

E&S: You mentioned bats that winter in caves, and you also mentioned that some bats set up breeding colonies in caves ….

Ms. Nutt: Yes, and you’re familiar with the Mexican Freetail bats [in Austin]. They have breeding colonies in caves in Texas.

E&S: Do you have Mexican Freetails?

Ms. Nutt: No, we don’t have them. The ones we have here [that are cave-dwellers], an example of another native species is the Gray Bat. It uses caves year-round and will use different caves throughout the year. They’ll use a cave with suitable winter conditions for them, where climate is appropriate for the winter hibernation period. Then come spring, they’ll use transitory caves, caves used in the period before they get to the breeding caves where they’ll set up maternity colonies. So, they have winter caves, they have summer caves, and transitory caves in spring and fall. In summer, they have a cave suitable for a maternity site, and if there are enough bats, they have large colonies. Gray Bats like to be in large colonies of females and young.

And some bats use bridges too, like the Mexican Freetails at Congress Avenue in Austin. Here in Virginia and the Carolinas there have been a number of people going out and doing what they call the “bats and bridges surveys.” The Virginia Game and Inland Fisheries Department has been working on surveying a number of bridges throughout Virginia in different geographic regions – coastal plains and western mountains – looking for bat use in bridges. And they suggest designs for bridges to the Department of Transportation, to make the bridges more attractive for bat use. There are designs that departments of transportation can access. I think Bat Conservation International in Texas has a person who specializes in bats and bridges, and they may have put out a publication on designing bridges to make them bat-friendly. If departments of transportation are interested, they can do that, and some do try to incorporate, wherever possible, features in bridges that are bat- friendly.

In Virginia, one of the bats they’ve found under bridges is the Eastern Small-footed bat, which is a bat that not a whole lot is known about. It’s not federally protected. It’s not very well-known. That particular bat will use caves and mines and will also roost in cracks and crevices in rocks, and under rocks on the ground. People have found it by picking up a rock on the ground and found a bat roosting under there. It’s one of our smaller bats.

Here in the district we’ve put up bat gates on mines and caves. We’ve done a lot of mist net surveys looking primarily for Indiana bats, but also do surveys of all the species that we capture. We’ve done some radio tracking – we put radio transmitters on some Indiana Bats during the fall back in 1999, when we did some fall roosting studies. We tracked them at night while they were foraging, doing some triangulation with radio telemetry, and tried to determine where the bats were flying to feed at night. And we do conservation in the community, we give talks on bats as we’re asked, for schools and community groups, and we have materials that we like to share with people.

E&S: Some of the bats migrate?

Ms. Nutt: Yes, they’ll move from north to south, to more southerly areas.

E&S: How far do they go?

Ms. Nutt: Red bats, for instance, will be much further north in the summer, but they’ll migrate to the Southern U.S. from New England and Canada.

E&S: Their primary source of food is insects?

Ms. Nutt: Yes, all of our bats in the Eastern U.S. are insectivore, all insect-eaters. One you get to the Southwest, you pick up some bats that are pollinators.

E&S: In your area, I presume the insect population is rather abundant!

Ms. Nutt: Yes. We have a lot of insects. We manage for good water quality on the national forest so we have mayflies and caddisflies that bats will forage for in our streams and water areas. And within the forest itself, we have a real diversity of insects. They continue to do more research on bat’s effect on insect populations because they do play such a big role. People don’t realize sometimes what animals are doing for them.

E&S: Can you identify bats by their call?

Ms. Nutt: There is some technology that allows you to record the echolocation calls of different bat species, and scientists are developing models so you can review those acoustic pictures and identify them by species. There’s a whole group of species, genera called Myotis. They’re very difficult to distinguish but [researchers are] working on making it easier to tell different species apart from each other.

We’ve got this equipment now where we can go and record [echolocation calls] directly into a laptop computer, or download it to a tape although there is some distortion when you download to a tape, and then play it back to a computer. We have a little microphone and it runs through the equipment and downloads these files to the computer. We then run the files through this program, and it shows a spectrograph, like a bird call, of these bat calls. You can do a survey that tells you the presence of these different species that are out there. It’s a really useful tool for detecting presence of species in places where you may not be able to mist net effectively.

E&S: The software you just mentioned for telling bat species apart, is this a technique currently in use?

Ms. Nutt: It is. I’m sure there are other companies but Anabat, a company in Australia, is making it. The equipment is called the Anabat. It’s being used in the U.S. by people in the Forest Service and I’m sure by researchers in and outside the U.S. as well. There are some people working on their PhDs right now, using this software and technology to help people do surveys and inventory for bats. Once you have the data, trying to decide what it means and what it’s telling you, that’s the difficult part. These people are doing their graduate work in putting these models together to say, OK, it’s this bat or that.

E&S: How else do you tell bat species apart?

Ms. Nutt: Mistnet surveys. [Mistnets are fine nets that are strung across open areas. Birds or bats flying into the nets get entangled in it. They are gently removed by researchers who then collect information about the animals – species and sex identification, measuring wing span and other physical features, weighing the animals, collecting blood or feces samples, etc.. Often, an identification ring is attached to the leg (called banding or ringing) before the animals are released.]

E&S: Do you set these nets really low, like for birds?

Ms. Nutt: You can set the nets in all different ways. We tend to set them when we’re doing our surveys near water, like over water holes or a stretch of stream, to catch the bats as they’re foraging for insects over the water or when they come in for a drink. It appears to be an attraction for them. The other place we set mistnets are on throughways, like a small dirt road running through the forest with a closed canopy above it. We’ll set nets across that because the bats will fly in those paths. We can set them low. There are methods to run them to the canopy using a pulley system, so you can raise and lower them, that way you can capture bats flying well above you.

E&S: The other kind of survey technique is identifying then visually?

Ms. Nutt: Right. In Virginia, the state conducts a winter survey of caves with endangered species once every 2 years, So that would involve going in one time every 2 years into a cave and doing a visual count of the bats, and identifying the species. It [provides a] trend analysis over the decades to see if the population is increasing, or stable, or decreasing. Of course, you can use night vision technology to count bats coming out of a roost location. So if you have a roost identified, you can sit there and watch the roost, whether it’s a tree or cave or mine opening, and count the individual bats as they come out using night vision.

E&S: When you’re visually watching the bats fly around, can you tell the species apart based on the way they fly?

Ms. Nutt: No. There would be clues that could give you a good idea or you may already have some other information about the roost location you’re watching them come out of.

E&S: What’s the status of some of the bats in your district? Which bats are you concerned about right now?

Ms. Nutt: In our forest in Virginia, the federal endangered species we’re most concerned about are the Gray bats and the Indiana bats. We have both those species on forest land. The Virginia Big-eared bat is the other species that’s also endangered.

E&S: The Virginia Big-eared bat, what kind of habitat does it need?

Ms. Nutt: It’s also a cave-dwelling bat and has really specific needs. This bat in Virginia is restricted to just a handful of locations.

E&S: Is it only in VA?

Ms. Nutt: No. This is a subspecies, the Virginia big-eared bat. But the species [Big-eared bat] has a wider range.

E&S: What are the ranges of the other bats you’ve mentioned?

Ms. Nutt: The Gray bat occurs in Virginia, Kentucky, Tennessee, Georgia, Alabama, and Missouri.

For Big-eared bats, there are several subspecies of it. Some subspecies are considered endangered as well. The Virginia Big-eared bat is found in West Virginia, the western mountain portion of Virginia, the eastern portion of Kentucky, northeast portion of Tennessee and northwest portion of North Carolina. It’s just that small range. It’s real isolated. The Western Big-eared bat and Ozark Big-eared bat have bigger ranges in other parts of the U.S..

The Indiana Bat has a large range in the East, they can go as far north as Vermont and New Hampshire, and all the way south to the northern panhandle of Florida. They extend to Tennessee, and westward to Oklahoma.

One more thing I want to mention … these bats have strong site fidelity to their caves, so the same colonies will return to the same cave each year unless something causes them to have to relocate. This goes for most [cave-dwelling] bat species. Some even return to the same location in the same cave. They’ve done some banding of bats, and they’ll find them in the same spot year after year!

E&S: How do people come to conclude that a particular bat species is endangered?

Ms. Nutt: They look at winter cave surveys from records from the ’50s, ’60s, and ’70s. And they compare [that data] with the numbers they’re [currently] seeing in those caves. And they’ve seen significant downward trends. Even the Indiana bats, right now, continues to have a somewhat downward trend although most of the significant high vernacular (winter) caves have been protected at this point with gates and other management strategies to keep people from disturbing them in the winter. But we’re still not seeing a big rebound in numbers, and nobody knows why. So there is a lot of effort being made to look at summer habitat, contaminants in the habitat, if there’s something going on that’s continuing to impact the species, not allowing it to recover.

E&S: How do you maintain habitat for bats?

Ms. Nutt: In the national forest in Virginia, we consulted with the U.S. Fish and Wildlife Service, and received a biological opinion. It was basically an assessment that looked at the whole forest – all the activity that we conduct, and what effect it may have on forest habitat that bats would be using for foraging and roosting. From that, we came up with some guidelines that we adhere to during our management activities. One of [the guidelines concern] shag bark hickory, a preferred roost tree. There’s not a lot of commercial value for shag bark hickory. We retain all shag bark hickory on national forest land during any sort of operation unless there is a safety hazard or some unusual circumstance.

In addition, when we do activities like timber harvesting, where we’re altering the forest structure, we retain a minimum average of 6 trees per acre, 9 inches or larger in diameter. That’s to provide for short-term and long-term roosting habitat so that we have existing trees out there, trees that will continue to mature. For those trees that we retain, we have an order of priority species that we would prefer. Obviously, species that are going to provide fluffing-type bark naturally are going to be preferred over a tight bark. White oak is another example of a species that has a bark that sometimes peels off and the bats would be able to roost underneath.

And then, where there is a cave, a winter hibernation site for the Indiana bat, we have management area boundaries around that cave. Within those boundaries, within 1 to 2 miles of the cave, we have certain conditions that go into effect. There is only so much regeneration-type timber harvesting that would occur in there, and there would be little or no road construction. These kind of things limit disturbance to that habitat that is very close to the cave, since it becomes very critical in the fall when the bats are getting ready to go into the winter, they tend to roost and forage near the cave entrance.

E&S: The bats that you’ve mentioned, the Indiana and Gray bats, what is their local range like?

Ms. Nutt: As far as how far they forage? There’s a guy out in the Midwest who has done some radio tracking of Indiana bats during their summer foraging. In the fall, what we found [in the district] was that they were staying about a 2 to 3 mile radius of the cave. So they would forage all around within that range, and roost in certain trees within that range. But they didn’t tend to go very far.

E&S: Could you describe how radio tracking is done?

Ms. Nutt: The transmitters are really small, maybe the size of your fingernail, and they have a thin whip-antenna that extends 3 to 4 inches. You attach the transmitter with eyelash glue, a non-toxic adhesive, and place it between the shoulder blades behind the back of the neck, so it does not interfere with flying. The whip antenna extends down their back. The transmitters, because they’re so small … you can get transmitters up to 21 days, but usually they last 11 to 14 days for the smaller transmitters, and 14 to 21 days for the larger transmitters. And of course it depends on the bat species, the large bat species get those big ones. The adhesive will wear off over time, and the transmitters drop off. I’ve heard of bats where transmitters were placed in the fall, and when doing a winter count, the transmitters were on the bats while they were in hibernation. But I expect that once they emerge in the spring and get active the adhesive would have dried up and fallen relatively quickly. The transmitters are powered by tiny batteries.

And of course we have receivers, and the way we’ve [tracked the bats] is that we try to have at least 3 people with receivers and antenna to pick up the signal. We try to triangulate – we go to set locations and try to triangulate as the bat flies around. We set the sequence [of readings], the timing of our readings, and we all take a reading at the same moment in time, so we can triangulate … we can track where that bat’s moving, so every 3 minutes, we take a bearing on a particular bat that we’re following for an hour so we’ll have a foraging track for an hour that we can plot on a map.

E&S: Each transmitter has a unique signal?

Ms. Nutt: It does. It comes from the company that you purchase the transmitters from. You set your receiver to that particular frequency and just rotate through the numbers to pick up the other frequencies. So you switch on and off through the night tracking different bats. Here in the mountains, there is a lot of bounce so the information we get we have to take with the understanding that we could be off by a fair amount depending on how much bounce the signal gets as it goes off the terrain.

E&S: So the radio tracking is done in a very limited window of time?

Ms. Nutt: Yes. So when we come in to do something like that, it’s a large investment of time and resources, because you really need to be available to track them, like spend the evenings tracking the bats for foraging locations, and during the daytime, track the signals to the tree location or wherever the bats are roosting at. Since we’re tracking Indiana bats, they roost in trees.

And we follow that information up … we usually mark that tree and we come back at a later date and follow-up with collecting data on habitat, characteristics of the roost tree, and habitat around the roost tree location, to see if we can detect trends or better quantify what habitat the species is using. And we’ll look for the location of the bat [in the tree], if it’s roosting high up the ground, if the bat’s in a cavity, under the bark, that kind of thing.

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Additional information From Lisa Nutt regarding bats at the Clinch Ranger District:

Bats inhabiting caves or mines during all or part of the year: Little brown bat (Myotis lucifugus) – winter Gray bat (Myotis grisescens), an endangered bat – occupy caves year round Northern long-eared bat (Myotis septentrionalis) – winter Indiana bat (Myotis sodalis), an endangered species – winter Small-footed bat (Myotis leibii) – winter, some summer use Eastern pipistrelle (Pipistrellus subflavus) – winter, some summer use Big brown bat (Eptesicus fuscus) – winter Rafinesque’s big-eared bat (Corynorhinus rafinesquii) – winter Virginia big-eared bat (Corynorhinus townsendii virginianus), an endangered species – year round

Tree bats which seldom enter caves/mines: Eastern red bat (Lasiurus borealis)
Hoary bat (Lasiurus cinereus)
Silver-haired bat (Lasionycteris noctivagens)

Forest dwelling bats:
Silver-haired bat – throughout the year
Eastern red bat – throughout the year
Hoary bat – throughout the year
Indiana bat – summer
Northern long-eared bat – summer
Eastern pipistrelle – summer
Rafinesque’s big-eared bat – summer
Big brown bat – summer also uses structures Little Brown Bat – summer, also uses structures Small-footed bat – summer

Bats that migrate:
Silver-haired
Eastern red bat
Hoary bat

Total bat species in southwest Virginia: 12