Thursday, August 02, 2007

Article: Bats rule the world

A flying fox bat takes off from its tree roost in Mysore, India

Last weekend I visited the most amazing location. I went to the place with the largest concentration of mammals anywhere in the world! I didn’t have to journey to the African Rift Valley or the rain forests of the Amazon. I didn’t even have to leave Texas. In fact, I only traveled about fifty miles from my home in Buda.

Maybe it’s not surprising that the largest concentration of mammals is composed of members of one of the most diverse mammalian groups, the bats. Bats, in the order Chiroptera, are only outdone in terms of numbers of species by the rodents. There are over 900 species of bats comprising about one fifth of all mammalian species. The bats at the world’s largest colony at Bracken Cave just north of San Antonio are Mexican free-tailed bats, the same species as the colony under the Congress Avenue bridge in downtown Austin.

Bats can be divided into two groups, the small microbats and the large macrobats. The microbats have a nearly world-wide distribution and include all of the 47 species of bats found in the US. These bats use echolocation (or sonar) and feed mainly on insects. The macrobats, also known as flying foxes, live in a swath from Australia, through Southeast Asia and Africa, including Madagascar and many oceanic islands. Flying foxes do not use echolocation and most species feed on fruit. As their names suggest, microbats are generally considerably smaller than megabats. The largest of the flying foxes have a wingspan of up to six feet. The smallest of the microbats, the bumblebee bat of Thailand, weighs less than a penny and is considered to be the world’s smallest mammal.

When I was a little girl living in Panama, we used to sleep inside netting, mostly to escape the mosquitoes but also to prevent vampire bats from biting our toes at night. The threat from vampire bats is not really the bite, which doesn’t hurt at all since the bats provide a local anesthetic, or the loss of blood since each bat drinks only about two tablespoons. The real issue is rabies, which is more common in vampire bats than in other bat species, as can be expected by their feeding habits. The United States is well outside the range of vampire bats and about one in five hundred bats here carries rabies. In the US, an average of one person per year contracts rabies from a bat.

Aside from the prospect of rabies, bats have a large impact on human life. The colony at Bracken Cave consumes an estimated 200 tons of flying insects each night. Many of those insects are crop pests. Several plant species such as mango, clove, guava and avocado depend on bats for pollination. The large flying foxes are also hunted for food throughout much of their range.

Watching the bats emerge from Bracken Cave is an awe-inspiring experience. For a couple of hours before sunset, the bats swirl around just inside the mouth of the cave. It takes several minutes to notice that the dark rocks on the outer lip of the cave are not dark at all, what you are really seeing is thousands of densely packed bats. Just before the sun goes down a few brave bats spiral out of the sinkhole containing the cave opening and fly off in lonely solitude. As the sun disappears, a thin trickle of bats winds its way across the darkening sky. Well before full-dark that trickle has become a torrent with a seemingly endless flow of bats streaming forth. The wind from their wings causes the nearby trees to sway as if a gentle breeze were blowing.

Central Texas is also fortunate to be the home of Bat Conservation International (BCI) which was founded in Austin in 1982. BCI is dedicated to bat conservation world-wide and owns nearly 700 acres surrounding and including Bracken Cave. Tours such as the one I attended are offered periodically throughout the summer. Visit their website for information on how to join a tour.

Bat Conservation International:
Flying Fox Conservation Fund:

Organization for Bat Conservation:

Photo: Opening of Bracken Cave with bats milling about before sunset.
Photo: The bats at Bracken Cave were coming out pretty thickly at this point although they came out in even greater densities after it was too dark to photograph them.
Photo: These microbats were roosting on a tree trunk in Venezuela.

Photo: Flying foxes heading out for a night of fruit feasting, near Labuanbajo, Flores, Indonesia. These large bats fly like birds rather than like small insectivorous bats like the Mexican free-tailed bats at Bracken Cave.Photo: Flying foxes roosting in trees in Mysore, India
Photo: From a distance the bats look like large hanging fruit.


kizzy said...

bats are neat!

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