Many species of bats in a cave in Trinidad.
Credit: Gerry Carter
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A
leaf-nosed bat from the New World. The purpose of the leaf structure
on the bat's face is not known for sure, but it may be important for
echolocation.
Credit: Brock Fenton
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A
vampire bat. Only three of the more than 1,100 species of bats are
vampire bats. Contrary to popular belief, vampire bats are not true
vampires because they do not suck blood. Rather, they cut a tiny slit in
their prey's skin with their razor-sharp front teeth and lick up the
resulting blood. Chemicals in the bat's saliva prevent clotting in order
to keep the blood flowing until that bat has consumed its fill, which
is generally less than an ounce. These anti-clotting chemicals are
currently being researched for possible use as anticoagulants for people
who are at high risk for blood clots, such as people who have recently
suffered strokes.
Credit: Brock Fenton
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The buds of this flower--a Pseudobombax ellipticum--open explosively at night and are primarily pollinated by bats.
Credit: Brock Fenten
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A
little brown bat is released by a University of California, Santa Cruz
graduate student. There are more than 1,000 bat species with varied wing
spans, weights and facial features. Bats account for about 20 percent
of all mammalian species.
Credit: Kate Langwig
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Hanging out: Hibernating little brown bats that have white-nose syndrome in a mine in New York.
Credit: Kate Langwig
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This
bat has a long tongue for nectar feeding. The ears of bats are shaped
to maximize detection of sound waves for echolocation. Bats emit sounds
for echolocation through their mouths or noses, depending on the
species.
Credit: Brock Fenton
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The sight of bats hanging upside down in creepy caves or fleeing in
fluttery flocks from their subterranean haunts at dusk like "bats out of
hell" may spook even the most rational, otherwise unflappable observer.
Nevertheless,
on every day (and night) but Halloween, these much maligned creaturesof
the night should be loved, not feared. Why? Because, contrary to
popular belief, bats do not attack people; bats do not tangle in
people's hair; and even vampire bats are not true vampires. (Vampire
bats lick blood but do not suck blood.)
What's more, unbeknownst
to most people, bats make important contributions to ecology, the
economy and even to the search for new technologies.
Important ecological roles of bats
Bats,
which live on all continents except Antarctica, are essential members
of many types of ecosystems, ranging from rain forests to deserts. By
fulfilling their ecological roles, bats promote biodiversity and support
the health of their ecosystems.
The ecological roles of bats
include pollinating and dispersing the seeds of hundreds of species of
plants. For example, bats serve as major pollinators of many types of
cacti that open their flowers only at night, when bats are active. In
addition, bats eat copious quantities of insects and other arthropods.
On a typical night, a bat consumes the equivalent of its own body weight
in these creatures.
Economic value of bats
As
bats fulfill their ecological roles, they provide many economically
important services. For example, bats serve as essential pollinators for
various types of commercially-valuable crops, including bananas, mangos
and guavas. In addition, bats consume many crop-eating insects and
thereby reduce farmers' need for pesticides.
All told, according to a
2011 study published in Science, insect
consumption by bats reduces the pesticide bill of the agriculture
industry in the United States by roughly $22.9 billion per year on
average. Another study,
partially funded by the National Science Foundation (NSF), calculated
the average annual value of Brazilian free-tailed bats as pest control
for cotton production in eight counties of south-central Texas at about
$741,000.
Inspiration for high-tech innovations
Bats
offer much to the field of biomimetics, which is the science of
modeling cutting-edge technologies based on natural forms. After all,
the development of sonar for ships and ultrasound was partly inspired by
bat echolocation. Echolocation is the navigation system used by most
bats to find and follow their quick-moving insect prey at night,
sometimes via daring aerial dogfights and speedy chases--all without
crashing into trees, buildings or other obstructions.
Here's how
bat echolocation works: A bat emits a structured high frequency sound,
usually beyond the range of human hearing, which bounces off surrounding
objects and then returns echoes to the bat. By comparing the delay and
structure of the echoes to those of the original sound, a bat can
calculate its own distance from the objects and determine size and shape
of those objects and thereby construct a three-dimensional map of its
environment.
Even though a bat's brain is only peanut-sized, bat
echolocation is so sensitive that a bat flying 25 miles per hour in
complete darkness would recognize differences in echo delays of less
than a microsecond, allowing the bat to distinguish even a junebug from
an underlying leaf, according to Universal Sense: How Hearing Shapes the Mind, which was authored by neuroscientist Seth S. Horowitz, whose earlier work was funded by NSF.
How
do bats stay focused on sonar echoes from their target prey without
being overwhelmed by the cacophony of echoes from other objects? That
question is answered by an NSF
video about recent research on bat echolocation.
Another
bat trait that provides potential grist for future application is the
flying ability of bats, which are the only mammals that can fly on their
own power. The aerodynamic repertoire of bats, which includes changing
flight direction by turning 180 degrees within just three wing beats
while flying at full tilt, would be the envy of any fighter pilot, said
Horowitz.
Bats are such nimble flyers because of the dexterity of
their wings, which--unlike insect and bird wings--are structured to
fold during flight, similar to the way that a human hand folds. Also,
their wings are draped by stretchy skin and are powered by special
muscles. Ongoing research about the structure of bat wings and the
mechanics of bat flight may ultimately lead to the development of
technologies that improve the maneuverability of airplanes.
A new, fast-spreading bat epidemic
The
multi-faceted importance of bats only compounds the tragic dimensions
of a new fatal epidemic in bats known as white-nose syndrome. The
disease, which is named for a fungal growth around the muzzles, wings
and other body parts of hibernating bats, was first discovered in the
United States during the winter of 2006-2007 in a popular tourist cave
in upstate New York.
Since then, the continually spreading
disease, which has reached the central United States and Canada, has
killed more than five million bats, including up to 95 percent of some
bat species in some locations. Scientists believe that white-nose
syndrome--which is currently incurable, untreatable and
unstoppable--will inevitably drive some bat species to extinction. The
disease is similar to a fungal epidemic that is ravaging frog
populations in the United States.
The white-nose fungus causes
skin lesions on the wings of hibernating bats, which may damage the
animals' hydration, electrolyte balance, circulation and temperature
regulation, ultimately causing death by starvation and dehydration.
Behavioral changes in infected bats include a failure to wake normally
in response to disturbances and premature emergence from hibernation.
The
white-nose fungus is known to have existed in bats in Europe before its
arrival in the United States. But, as far as scientists know, the
fungus does not kill European bats, possibly because European bats
species are genetically protected from the disease. Because the presence
of the disease-causing fungus in Europe predates its arrival in the
United States, and because the fungus was first found in the United
States in a tourist cave, scientists suspect that the disease was
imported to the United States from Europe, perhaps on the clothing or
equipment of traveling cavers.
Differences in susceptibility
White-nose
syndrome is currently known to affect six North American bat
species--two of which are less susceptible to the disease than the four
others. With NSF funding, Marm Kilpatrick of the University of
California at Santa Cruz, Kate Langwig of the University of California,
Santa Cruz and Boston University and their colleagues are currently
working to identify the reasons for these differences in susceptibility.
So far,
a recent study
led by Langwig showed that social behavior may influence mortality
rates. Specifically, the study indicates that as the size of infected
colonies shrinks because of deaths from white-nose fungus, death rates
within colonies of species that hibernate singly tend to stabilize. By
contrast, death rates within colonies of species that hibernate in
tightly packed groups do not.
Amazingly, the research also has
shown that the little brown bat, a species common in the northeast of
North America and widely affected by white-nose syndrome, has been--for
unknown reasons--becoming less gregarious, going from a species that
tended to hibernate in dense clusters to one that now tends to hibernate
singly. By changing their behavior, these bats may be reducing disease
transmission within their colonies and thereby saving themselves from
extinction. By contrast, the Indiana bat, a gregarious species that is
listed as an endangered species, is continuing to hibernate in dense
clusters and will therefore probably go extinct.
"Our research
gives us an indication of which species face the highest likelihood of
extinction, so we can focus management efforts and resources on
protecting those species," said Langwig. For example, the U.S. Fish and
Wildlife Service is incorporating Langwig's study results about little
brown bats into ongoing deliberations about whether to classify the
species as endangered.
Kilpatrick and Langwig are currently
researching other factors, in addition to social behavior, that may
influence disease susceptibility. One possibility, Kilpatrick says, is
that some bat species are less susceptible to white-nose syndrome
because their skin hosts bacterial communities that have anti-fungal
properties and so protect them from the white-nose fungus.
In
addition, Kilpatrick is currently investigating whether and how
particular microclimates in caves and mines used by hibernating bats may
be affecting the spread of white-nose syndrome. "Some bat species or
some individual bats may prefer to hibernate in caves or mines that are
relatively hot or cold, or wet or dry," Kilpatrick said. "We want to
know whether such environmental conditions impact susceptibility to
white-nose syndrome."
Impacts of bat losses
Other
topics that are ripe for research involve the responses of ecosystems
to plummeting bat populations. "Insect populations are very variable,"
said Langwig. "So in order to identify the impacts of bat declines on
insect populations, we would need many years of data on insect
populations before the arrival of white-nose syndrome as well as many
years of data after its arrival for comparison." But because white-nose
syndrome is so new and has spread so fast, scientists do not yet have
enough data to determine how the absence of bats will impact their
ecosystems, he said.
Other threats to bat survival besides white-nose syndrome
Other
threats to bat survival include the use of pesticides and insecticides,
habitat loss and the hunting of bats for bushmeat in some regions. In
addition, for reasons that are not fully understood, migrating bats are
apparently attracted to wind turbines; large numbers of bats have been
killed on wind farms in recent years.
More bat facts
Learn more about bats from a Halloween
chat with Horowitz sponsored by The Washington Post.
Investigators
Thomas Kunz
Kate Langwig
James Simmons
Seth Horowitz
Gary McCracken
Jeffrey Foster
Winifred Frick
A. Marm Kilpatrick
Related Institutions/Organizations
Brown University
Trustees of Boston University
Total Grants
$895,322
The National Science Foundation (NSF)
ayabaca@gmail.com
ayabaca@hotmail.com
ayabaca@yahoo.com
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