Tuesday, September 19, 2006

World's Largest Bat Colony

With a population of around 20 million, Bracken Cave is home to the largest bat population in the world. For over 10,000 years, pregnant Mexican free-tailed bats (tadarida brasiliensis) have been migrating north to this cave just 20 miles from downtown San Antonio, Texas to use this spot as their hatchery.

In June the expectant mothers give birth to one pup, spend about an hour getting acquainted with their baby's smell and sound and then park it in the nursery where the pups hang in tight clusters of approximately 500 per square foot. Amazingly, the mothers and the babies recognize each other and get together at least twice a day for nursing.

In the evenings the moms leave the cave to go hunting for food, and when the pups are about 5 weeks old, they'll join the flight. There are so many of them that it literally takes hours for the cave to empty, and the flapping of their wings produces a sound like an overhead river. The cloud of bats is so dense that it shows up on weather and airport radar on a nightly basis. They fly and eat, fly and eat, all night long -- covering thousands of square miles and consuming up to 250 tons of insects per night.

Take just a second to think about this: how many insects does it take to make a pound? A lot. And how many pounds in a ton? 2000. Multiply that by 250 and that's 500,000 pounds of insects every single night for the duration of their stay -- which is usually about 6-7 months. That totals out to approximately 48,750 tons (97,500,000 pounds) of Texas insects annually devoured by this colony alone!

When the weather turns frosty, the moms and the weaned pups head back to Mexico where they spend the winter.

Bracken Cave is currently owned by Bat Conservation International.



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