to Bat for BATS
misunderstood, bats still rank among the least-studied
and least-loved animals. But thanks to the efforts of
Bat Conservation International along with the National
Park Service, bats are gradually gaining more respect.
WHAT DO limestone passages in Carlsbad Caverns and
within the Mammoth Cave system, abandoned mines in the Great
Smokies, and rainforests in American Samoa have in common? In
addition to being managed by the National Park Service, these
diverse habitats all host bat maternity colonies.
Worldwide, bats account for about one-quarter of all
mammal species. But with nearly a thousand types identified, bats
still rank among the least-studied and least-loved animals. Dr.
Merlin Tuttle, founder of Bat Conservation International (BCI), is
out to change that. BCI promotes bat research and protection, and
largely through partnerships with federal agencies such as the
National Park Service—which is also committed to biodiversity
and the essential role bats play in ecosystems—bats are
gradually gaining more respect.
Myths and superstitions often mask the truth that
bats are clean, intelligent, and beneficial. The little brown bat,
a common species in much of North America, can devour 600
mosquitoes per hour. Long-nosed bats of the Southwest pollinate
and disperse seeds of important plants including agave and organ
pipe and saguaro cacti. In American Samoa, a third of the tropical
tree species depend upon bats for pollination or seed dispersal.
Bats also pollinate bananas, avocados, dates, figs, mangos, and
cashews, and their contribution to commercial agriculture through
natural insect control is worth millions of dollars annually.
Among the 45 species of bats native to the United States,
six are endangered, and several more are proposed for
protection. Tuttle says, "Bats suffer from habitat loss
and environmental pollution, but the primary cause of their
decline is destruction by humans acting out of fear and
ignorance." Some bats gather in large maternity
colonies or hibernate together in winter, and these
assemblies are especially vulnerable to disturbance. Bats
reproduce so slowly—usually only one pup per female per
year—that when a colony is vandalized, it may not recover.
About 60 sites within the National Park System have caves that
provide essential living space for bats. In 1995 BCI and the
National Park Service (NPS) signed a memorandum of understanding
to develop bat conservation, research, and educational projects.
Since then, BCI experts have participated in many bat population
surveys and provided technical expertise for such improvements as
bat-friendly cave gates.
At Mammoth Cave National Park in central Kentucky,
bat-friendly cave gates have started to rectify a problem that
began decades ago when the cave was mined for nitrates and became
a tourist attraction.
Discovered by colonists in the 1790s, Mammoth Cave's
bat guano-enriched sediments provided a valuable source of
nitrate, tons of which were removed for use in gunpowder for the
War of 1812. About that time, sightseers began touring the cave.
An 1810 newspaper article refers to bats being "crowded so
close that they resembled a continued black cloud." When Yale
biologist Benjamin Silliman, Jr., visited in 1850, he estimated
them by the millions.
But by June 1996, when park researchers invited BCI's Tuttle to
accompany them into Mammoth Cave, evidence was scarce. On cave
walls and ceilings, scientists discovered reddish marks where
roosting bats had stained the rock. Scientists also found and
dated remains in many parts of the cave.
Analysis of bones indicated primary use by
hibernating Indiana bats, with some gray bat summer roosts in
warmer rooms. Using a formula of 300 Indiana bats per square foot
of roosting space, researchers estimated that as many as 20
million Indiana bats could have used these passages in the past.
According to Tuttle, Mammoth Cave was once possibly
the world's largest and most important Indiana bat hibernation
Mammoth's relationship with Indiana bats is
especially important because they, along with gray bats, are
endangered. This status means that they are accorded special
protection under laws enforced by the U.S. Fish & Wildlife
Service (USFWS) and ensures that habitats used by these animals
receive protection. Areas occupied by the endangered species may
also be seasonally or permanently closed to visitors to prevent
USFWS surveys in 1993 showed that Indiana bat populations
nationwide had declined 41 percent during the previous decade.
Indiana bats inhabit riparian forests in New England and the
Midwest in summer, then in winter they seek caves with stable
temperatures between 37 and 45 degrees Fahrenheit. Individuals
often rest in the same place on the same cave wall winter after
winter. Most Indiana bat hibernacula are located in Kentucky,
Missouri, and Indiana, where only 3 percent of all caves provide
suitable conditions. About 85 percent of the Indiana bat
population now winters in just seven caves, several of which are
located within Mammoth Cave National Park.
About 350 miles of passages at Mammoth have thus far
been mapped. As recently as 1947, Long Cave—one of those caves—sheltered
more than 50,000 wintering Indiana bats. But when a concrete wall
and heavy entrance door were installed there 35 years ago to
prevent vandalism, temperatures rose and bat use declined. Five
years ago, at the urging of BCI and the USFWS, park managers
designed and installed bat-friendly gates at the entrances of Long
as well as Dixon, Colossal, and Bat caves. Since then, the
wintering populations have increased. Long Cave now hosts about
650 Indiana and 400 gray bats in the winter. Colossal, which lost
95 percent of its Indiana bats between 1950 and 1995, now shelters
about 350 of the animals in the winter. Dixon Cave, near Mammoth's
historic entrance, hosts a fairly stable winter population of
5,500 Indiana and 500 gray bats.
Although Indiana bats do not presently hibernate
within Mammoth Cave itself, park ecologist Rick Olson expects they
will return in time. Originally the cave had a cool, moist, stable
environment. It "breathed" in winter when cold air
poured in at lower levels and air warmed by interior walls escaped
from higher openings. When large sheets of metal were seasonally
placed over the entrance to keep winter tourists warmer,
temperatures in passages formerly occupied by hibernating bats
increased above their tolerance.
Now, park employees have installed a USFWS-approved
gate that allows bats to pass easily while significantly restoring
the historic air flow. A network of cave atmospheric monitoring
stations collects data to gauge progress of the environmental
restoration effort. Because biologists know what temperature range
Indiana bats need to survive in hibernation, they have a target
for fine-tuning the gates until this microclimate is duplicated.
In hopes that a quieter scene will entice bats to
return, winter tours in part of Audubon Avenue have been
discontinued. Outside near the cave entrance, signs discourage
visitors from disrupting bats.
"Our main goals," says Olson, "are to
restore bat habitat and minimize disturbance. We don't really know
how Indiana bats discover places to hibernate, but we have been
encouraged by three new sightings."
Three bats are a far cry from the millions that once roosted here,
but their presence is a very positive sign. The park, Olson says,
hopes to emulate the success of Wyandott Cave in southern Indiana,
where Indiana bat populations are increasing, even though winter
tours of the cave continue.
Carlsbad Caverns National Park in southeast New
Mexico is host to 15 species of bats, including the famous summer
colony of Mexican free-tailed bats. Each summer 70,000 to 80,000
visitors watch the evening spectacle of Carlsbad's bat outflight
while interpreters talk about the animals' key role in the
ecosystem. These insectivorous bats migrate to Mexico for the
winter. Park scientists are examining the foraging range and diet
of the summer colony, determining population trends through
infrared photography of the roost, and investigating the status
and condition of winter roost sites in Mexico.
Bat populations at Carlsbad declined during the
middle of the last century, in part, because of poisoning from
DDT, a widely used agricultural pesticide that accumulated in the
bats' brain and body tissues. Although the use of DDT has been
banned in the United States and Mexico, soil residues from this
long-lived chemical and the current use of other insecticides may
still pose a threat to bat populations in the Southwest.
Before 1981, shafts drilled to facilitate guano
mining at Carlsbad Caverns made the cave unacceptable to millions
of Mexican free-tailed bats that formerly lived there. Then, the
National Park Service sealed the shafts, providing better habitat
for the remaining 250,000 bats. Recent infrared photo-censuses
show 300,000 to 500,000 free-tailed bats now roost there each
Although caves are among the most common habitat for bats, the
animals also roost in trees and other structures. One type of
structure, abandoned mines, has provided an unexpected housing
bonanza for bats.
According to the NPS Geologic Resources Division,
more than 10,000 abandoned mines are scattered throughout the
National Park System. Sheryl Ducommon, director of BCI's North
American Bats and Mines project, believes that 10 to 15 percent of
these receive substantial bat use.
In the past, mines were often sealed without
consideration for wildlife. Now, Ducommon and BCI's Dan Taylor
visit several parks annually to assist with mine surveys.
"Western parks are under tremendous
pressure," says Ducommon. "They have hundreds of mines
with safety and bat concerns." Since 1994, BCI has offered
nearly 20 regional Bats and Mines Workshops to train employees
with federal and state agencies how to safely assess these
Noteworthy mines in Organ Pipe Cactus National
Monument and Coronado National Memorial, both in Arizona,
safeguard lesser long-nosed bats. These endangered bats feed on
the nectar and fruit of saguaro cactus in late spring at Organ
Pipe, where there is a maternity colony of 8,000 to 15,000
females. Some 3,000 to 30,000 long-nosed bats visit Coronado in
late summer to feed on agave nectar.
At Big Bend National Park, Texas, where the
hazard-filled Mariscal mercury mine descends 450 feet underground,
Ducommon surveyed a Townsend's big-eared bat maternity roost there
that shelters about 10,000 bats—making it the largest big-eared
bat maternity colony in the United States. BCI also consulted on
the ten gates that maintain good air flow and bat access while
securing the mine from visitors, as well as providing interpretive
signs outside the mine.
Wildlife biologist Raymond Skiles is delighted with
the attention being given to bats at Big Bend. Scientists from the
University of Texas have recently identified the yellow bat as a
new species for the park and the state. The USFWS is also funding
an international study of the Mexican long-nosed bat with Dr.
Arnulfo Moreno. "These bats were listed as endangered in late
1980s, but this is the first true look at the bat on a range-wide
basis," Skiles states. "We are now shining a long-needed
spotlight on a group of animals that has been neglected."
More good bat news is emanating from other NPS sites.
The largest hibernating colony of gray bats west of the
Mississippi River uses Bonanza Cave near the boundary of Ozark
National Forest and Buffalo National River. Bonanza shelters
250,000 gray bats annually, roughly 15 percent of the known
population. Cave Mountain Cave normally hosts 100,000 wintering
gray bats, but last year 160,000 to 200,000 individuals hibernated
there. Geologist Chuck Bitting says, "Gray bats are
responding favorably to protection. Maternity colonies seem to be
doing well, with slightly more bats counted each summer."
In addition, big-eared bats have moved into talus
caves at Pinnacles National Monument in California. In response,
managers closed the area to safeguard the bats and wrote a concise
bat management plan, now a prototype for other parks. At Joshua
Tree National Park, mine surveys have protected California
leaf-nosed bats, and similar work at Death Valley National Park
has secured Townsend's big-eared bat maternity roosts and the
largest hibernaculum known in the California desert. With BCI
matching funding and technical assistance, a cave at Grand Canyon
that once sheltered Arizona's most productive big-eared bat
nursery has been gated. After years of absence, more than a
hundred big-eared bats and four other species have returned.
Finally, at Great Smoky Mountains, planning is under way to
protect a maternity roost and the hibernaculum of the largest
known colony of eastern big-eared bats.
"Bats are among the most gentle, beneficial, and
necessary animals on earth," BCI founder Merlin Tuttle
summarizes. "Wherever bats are found, they are essential
elements in nature's delicate web of life." With BCI and NPS
working together, the outlook for the protection of bats and their
ecosystems in the 21st century is considerably more positive than
it was a hundred years ago.