SCIENCE

These Bats Use Sonar to Jam the Signals of Their Rivals

How hungry Mexican free-tails sabotage the competition

April 2015

A large colony of Mexican free-tailed bats can consume an estimated 250 tons of insects in a single night. John C. Abbott; Rolf Nussbaumer; Joel Sartore / National Neographic Creative (2)

Known for their spectacular hunting sprees, when many thousands wing out of caves at twilight in search of insect prey, Mexican free-tailed bats now have a new claim to fame: Recent research shows that they are able to sabotage the sonar systems of rival bats trying to capture a meal.

Aaron Corcoran, a biologist currently at Wake Forest University, was studying the hunting habits of Mexican free-tailed bats in Arizona and New Mexico when his ultrasonic microphones picked up an unfamiliar sound. Bats use a variety of calls—most of them are inaudible to humans—for both navigation and communication, but the free-tailed bats sent this particular signal only when nearby bats were about to snag their prey.

So Corcoran and colleague William Conner, who studies animal communication, tethered live moths to a streetlight with lengths of fishing line and waited. When approaching bats emitted their characteristic “feeding buzz”—a rapid series of echolocation calls that bounce off a prey item and back to the bat—the researchers played recordings of the newly discovered call through loudspeakers. It dramatically reduced the bats’ chances of capturing the moths, shrinking their hunting success rate from about 65 percent to 18 percent. The call, which spans multiple frequencies, overlaps with the feeding buzz, creating a blur of noise that “jams” the echolocation signal, much as military forces jam enemy radio communications.

To be sure, other bat species also have specialized vocalizations for keeping competitors away from food. A common bat in North America, known as the big brown bat, makes a series of chirps that appear to claim dibs on flying insect prey, and pipistrelles in Europe emit complex sounds to warn other bats away from a patch of rooftop or urban park, along with the food resources within.

But Mexican free-tails, which live in enormous colonies that can exceed a million individuals, are the only echolocating animal known to actually jam signals. Corcoran, who describes bats as “incredibly adorable,” speculates that the adaptation evolved in response to the intense competition among members in the same crowded colony. “At some density,” Corcoran says, “your friends become your enemies.”