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Bats
are some of the most diverse and misunderstood mammals on
the planet today. They inspire fear and disgust and
are often persecuted because of it.
People's
fear of bats is probably derived of myths, concerns over the
spread of disease and because they are simply so different than
humans, as well as every other mammal.
White-throated Round-eared Bats roosting in a termite mound -
Lophostoma silvicolum
Until
the 1960's scientists didn't know much about bats. It was not until
they discovered bats could be captured in Japanese Mist Nets that
serious studies on them became possible.
Bats certainly are unique.
They are the only mammals with the ability to fly. Among their ranks
are the only mammals that subside chiefly on pollen and nectar and,
of course, those that feed exclusively on blood.
When looking at the benefits
provided by bats and comparing them with their negative aspects, one
quickly realizes that bats play an essential role in maintaining a
balance in our environment. Their benefits far outweigh any of
their negatives. |
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Bats'
ability to fly is one of their most amazing adaptations.
Their hand has evolved into a wing covered with a stretchy,
leathery, and very durable membrane. T
he word Chiroptera, which
is the name of their Order, literally translates into
"handwing".
This is strikingly clear
when viewing the photo on the left.
The bats fingers are extremely large and run from wrist
to the bottom of the wings while the thumb sticks straight up
and is not covered by the leathery membrane that covers
the other four fingers.
Another incredible
adaptation is their ability to navigate by using
echolocation. Echolocation works the way a sonar radar
would. Bats emit high frequency sounds. The sound in
turn bounces off their surrounding environment and returns
to them. The sounds are emitted by way of the bats mouth
and nose and may travel at
approximately 340 meters per second! The bats then analyze the time it takes for the
echoes to return to them and are able to tell
how far away an object is. This gives the bats a perfect
picture of their surroundings even on the darkest nights. |
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With about 1400
identified species, bats are the second most diverse mammal
group, second only to rodents. They
are found in every continent except Antarctica and make up about
one quarter of all mammal species.
Pale Spear-nosed Bat - Phyllostomus discolor
Nearly half of the mammals in Costa Rica are bats. We have 117 confirmed species in
Costa Rica, about eight percent of the world's known bat
species. Out of the 117 bat species present in Costa Rica, 80 have been
collected on the Osa Peninsula. This number is quite remarkable
when you think about it. The United States, which has 150 times
the landmass of Costa Rica, only has 47 bat species and the
entire continent of Australia only has 70 recorded species.
In Costa Rica, there is
great diversity among bats. They differ in where they hunt, how
they breed and what they eat. They range in size from the tiny
Black Myotis (Myotis nigricans), which has a wingspan of
about 5 centimeters and weighs about 5 grams, to the False
Vampire (Vampyrum spectrum), which can have over 80
centimeters in wingspan and weigh about 200 grams. The False
Vampire feeds mainly on sleeping birds and can take Motmots,
Pigeons and Parrots weighing about as much as the bat does!
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 A
large variety of bat species means a high degree of specialization
among them. Individual species usually stick to certain
height levels of the forest when they forage. Some may forage over the
water or way above the forest canopy. The height and location in
which they forage is dictated by their very specialized diet. In
Costa Rica about 53 percent of bat species feed on insects, 25
percent feed primarily on fruit, 10 percent eat mostly nectar
and pollen, about 7 percent feed on other vertebrates or their
blood, and at least 5 percent are omnivores.
What
they eat will in turn dictate when and how they breed. Female
bats give birth while roosting and the pups are usually born tail
first. After their feet emerge, they will clamp onto the
mother's fur and help pull themselves out. Newborn pups may
weigh as much as 40 percent of their mother's body weight!
Note the baby being nestled underneath the Brazilian Long-nosed Bat (Rhynchonycteris
naso) female at the bottom of the row of bats pictured
on the right.
Research seems to
indicate that bats time their reproductive cycles so that their
offspring is weaned at a time of year when food is most
abundant.
Insectivores usually have
only one litter per year and it is normally at the end of the
dry season. This way the pups will be weaned by early rainy
season when a large amount of insects are available to
feed on.
One of our smallest bats, the Black
Myotis (Myotis nigricans), breaks this pattern. It is
unique in that females may have up to three litters per year.
These bats are insect eaters, but they manage to produce litters
continuously throughout the year with a short pause at the end
of rainy season.
Because in the tropics
flowers and fruit are available most of the year, bats that feed
on fruit and nectar usually have a litter at the end of dry
season and another litter late in the rainy season.
Commissaris's Long-tongued Bat
- Glossophaga commissarisi
Finally, the Common Vampire (Desmodus rotundus) will
breed throughout the year, with individual females producing
about two litters per year. These bats enjoy a stable food
source and are unaffected by the changing of the seasons.
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Bats
generally have cryptic coloration and their fur is usually adorned
with different shades of black or brown. Greater Bulldog Fishing Bats (Noctilio leporinus)
have beautifully colored orange fur. We also have two species with
white fur, which is unusual among bats. The Northern Ghost Bat (Diclidurus
albus), which is found on the Osa Peninsula, and the Honduran
Tent-making Bat (Ectophylla alba) which is only found on
the Caribbean Slope. These tiny bats are about the size of
a wine cork and with their fuzzy white fur and yellow ears and
nose are probably the most beautiful bats in the country.
Honduran Tent-making Bats -
Ectophylla alba
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Another amazing
bat group are Disk-winged Bats (Thyropteridae).
These bats are unique in
that they are the only bats in America that roost right side up. They have
suction cups on their thumbs and on their heels which allow them to
stick to smooth surfaces. We have found them sticking to the smooth
tile on our bathroom wall! 
Spix's Disk-winged Bats - Thyroptera tricolor |
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There are two species of Disk-winged Bats in Costa Rica, both are
aerial insectivores and both species are found in Drake Bay. Spix's
Disk-winged Bats roost inside new, rolled up, heliconia leaves in
the process of unfurling. After the leaf has opened too wide for the
bats' taste, they move on to another leaf.
Peters' Disk-winged Bats are rare to see, but we have also found
them in Drake Bay. These tiny bats live in small colonies and
usually roost inside cones which form on dead banana leaves. We
found and photographed the colony of Peters' Disk-winged Bats shown
below in Drake Bay.
Peters' Disk-winged Bats - Thyroptera discifera |
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The Fringe-lipped Bat (Trachops
cirrhosus) is another incredible bat that is well worth
mentioning. This bat also feeds on insects, but is a specialist
on frogs. It locates calling male frogs, not by echolocation, but by
using its sense of hearing. Studies have shown that the bat can
distinguish between toxic frogs and edible ones based solely on
their call. Researchers have carried out experiments where they play the calls of toxic frogs that don't live in the area and the
bat still knows to avoid them! If they play calls of edible frogs,
the bat will violently attack the speakers! Scientists think the
bats can distinguish between the two based on the frequency of
the frog's call.
Fringe-lipped Bat - Trachops cirrhosus
After learning a little bit about these exceptional animals, it is
easy to quickly develop a passion for bats. Their diversity in
shape, biology, and abilities are nothing short of extraordinary.
Not only are they fascinating, but they are incredibly beneficial to
humans and the environment. |
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Insect eating bats play a crucial role in controlling insect
populations. Insectivore bats consume a huge numbers of
insects that could potentially cost farmers and foresters
billions of dollars and spread disease among humans. It is
estimated that just the 20 million Brazilian Free-tailed
Bats that inhabit Bracken Cave, in Texas, devour some 225
metric tons of insects every night!! On average a family car
weighs about 1.5 metric tons, meaning that this bat colony
alone consumes approximately the weight of 150 family cars
in insects per night, a truly a staggering feat!
Northern Big-eared Bat roosting in a
hollow tree - Micronycteris tresamici
Little Brown Bats often
eat mosquitoes and can catch up to 1,200 small insects per
hour. A typical Big Brown Bat colony can consume enough
Cucumber Beetles to avoid tens of millions of the beetle's
larvae depleting a farmer's crop. Imagine a world
without bats. The guano produced
by these insectivore bats is also a valuable fertilizer.
Female Northern Ghost Bat with her
pup - Diclidurus albus
It
is estimated that bats are responsible for the pollination
and seed dispersal of hundreds, possibly thousands, of
trees and plants.
Plants and trees like Ficus, Cecropia, Solanum, and
Piper depend on bats for seed dispersal.
Scientists estimate that Balsa Trees (Ochroma pyramidale)
rely solely on nectar and pollen eating bats for
pollination.
Fruit eating bats play a key role in regenerating forests.
Unlike birds, who normally defecate while perching,
bats tend to defecate in flight. This means that seeds
will fall to the ground and develop far from the shade of
the parent tree, perhaps in an open field.
Mesoamerican Tent-making Bats -
Uroderma convexum
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Unfortunately, bat populations are declining worldwide. The
causes are the usual suspects: global warming, destruction
of habitat, human persecution, pollution and the use of
pesticides. Pesticides are especially harmful.
They are used
on the insects that are consumed by bats, and end up
poisoning the bats. This has led to serious declines in some
areas.
Another budding danger to bats is the growing number of wind
turbines being erected to harvest electricity.
It
seems that bats, unlike the birds that hit them by accident,
may be attracted to the turbines.
One study in West Virginia in a site with 44 turbines
documented between 1,300 and 2000 bats killed during a six
week period.
But perhaps the most troubling development for bats in the
last few years is White-nose Syndrome. This mysterious
disease has killed tens, perhaps hundreds of thousands of
bats in North America. Up to 95 percent of the population of
infected bat colonies are being wiped out throughout
hibernation caves in New York, Vermont, Massachusetts,
Connecticut, and possibly Pennsylvania. They call it
White-nose Syndrome because infected bats exhibit a white
fungus on their noses.
The scariest thing is that scientists have no idea what
is causing this bat epidemic or how to stop it. Infected bats
are leaving their hibernation caves earlier than normal in a
severe state of emaciation and dehydration. Many also have
wing injuries, apparently acquired during their hibernation,
and the bulk of the bats belonging to infected colonies are
usually discovered
lying dead on the cave floors.
We encourage all of our readers to visit the Bat
Conservation International Website at
http://www.batcon.org/home/default.asp
and find out what you can do to help save these remarkable
animals. It is time we realized how important bats really are
to
our planet and take the necessary steps to protect these
wonderful creatures.
The following pages are dedicated to four of the most commonly
seen
bats on the Osa Peninsula:
Tent-making Bats,
Greater Bulldog Fishing
Bats, White-lined Bats, and
Brazilian Long-nosed Bats. All
bats appearing on these web pages are live specimens
photographed in the wild. The photograph of the Pale
Spear-nosed Bat at the top of the page was mist-netted at
Sylvan Falls and was being handled by Fiona Reid.
References:
Bat Conservation
International Website Articles
Available at:
http://www.batcon.org/home/default.asp
Beletsky, L.
2005 Travellers' Wildlife Guides Costa Rica
Interlink Publishing
Janzen, D. 1983 Costa Rican Natural History
University of Chicago Press
LaVal, R. & Rodriguez, B. 2002 Murcielagos de Costa Rica/Bats
Editorial INBio
Wainwright, M. 2002 The Natural History of Costa
Rican Mammals Zona Tropical
Wilson, D. 1997 Bats in Question Smithsonian
Institution Press
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