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The Mexican Free-Tailed Bat
| Article
# : |
14568 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
3 / 1988 |
873 Words |
| Author
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Merlin D. Tuttle
Merlin D. Tuttle is founder and science director of Bat
Conservation International in Austin, Texas. |
The Mexican free-tailed bat is one of nature's most remarkable and important animals. A small creature weighing less than half an ounce, it congregates in the largest colonies of any warm-blooded animal. It migrates south into Mexico and Central America for the winter, returning to northern Mexico and the southwestern United States each spring.
Despite the continued presence of vast numbers, this bat population has declined alarmingly over the past 20 years. Most of the remaining U.S. population relies on only about a dozen unique caves for survival. These caves are occupied by nursery colonies of at least a million or more bats each. The largest of these colonies contains in excess of 20 million individuals, an equivalent of approximately 240 metric tons of bats.
Large numbers are important to the bat's survival, since their combined body heat is required to create the incubator-like conditions necessary for successful rearing of young. Inside their cave roosts, they may cover thousands of square meters of walls at densities of approximately 1,800 adults per square meter. When the mothers give birth, densities of newborn pups may be in excess of 5,000 per square meter.
Survival for a young free-tailed bat is difficult at best. Imagine the problems a mother encounters in just finding her own pup. For some 20 years, biologists actually believed that this was impossible, and that mothers simply "herd nursed" any pup they found. Recently, scientists have demonstrated that, despite all the vast numbers and area covered, each mother remembers, within a few centimeters, where she left her young. As she returns from feeding, her pup identifies her voice from among countless others, rears up and calls, is recognized, and finally is confirmed by scent.
Each mother produces just one pup per year. It weighs close to a third as much as its mother at birth, the equivalent of an average human mother giving birth to a 40-pound baby. The pup is nursed from pectoral breasts, just as are humans, and grows very rapidly, first flying at about one month.
Imagine the incredible difficulty of simultaneously learning to fly and navigate with echolocation (a type of sonar) in the darkness of a cave, amid tens of thousands of other fast-flying bats, all jamming the airwaves with their own signals. The bats' vision, which is actually quite good, is of little help in a dark cave. On its first attempt, a young bat, traveling at some 20 feet per second, must
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