In nighttime flying duels, Mexican free-tailed bats make short, wavering sirenlike waaoo-waaoo sounds that jam each other’s sonar.
These “amazing aerial battles” mark the first examples of echolocating animals routinely sabotaging the sonar signals of their own kind, says Aaron Corcoran of Wake Forest University in Winston-Salem, N.C. Many bats, like dolphins, several cave-dwelling birds and some other animals, locate prey and landscape features by pinging out sounds and listening for echoes. Some prey, such as tiger moths, detect an incoming attack and make frenzied noises that can jam bat echolocation, Corcoran and his colleagues showed in 2009 (SN: 1/31/09, p. 10). And hawkmoths under attack make squeaks with their genitals in what also may be defensive jamming (SN Online: 7/3/13). But Corcoran didn’t expect bat-on-bat ultrasonic warfare.He was studying moths dodging bats in Arizona’s Chiricahua Mountains when his equipment picked up a feeding buzz high in the night sky. A free-tailed bat was sending faster and faster echolocation calls to refine the target position during the final second of an attack. (Bats, the only mammals known with superfast muscles, can emit more than 150 sounds a second.) Then another free-tailed bat gave a slip-sliding call. Corcoran, in a grad student frenzy of seeing his thesis topic as relevant to everything, thought the call would be a fine way to jam a buzz. “Then I totally told myself that’s impossible — that’s too good to be true.”
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Five years later he concluded he wasn’t just hearing things. He and William Conner, also of Wake Forest, report in the Nov. 7 Science that the up-and-down call can cut capture success by about 70 percent. Using multiple microphones, he found that one bat jams another, swoops toward the moth and gets jammed itself.
Corcoran says that neighborly sabotage could be especially valuable for the highly sociable Mexican free-taileds (Tadarida brasiliensis). “If you live in a cave with a million bats,” he says, “you have to go out and find food — and compete with a million bats.”
JAMMED SIGNAL Three video clips filmed outdoors at night show Mexican free-tailed bats (the larger white shapes) hunting tethered insects (smaller white shapes). The first clip shows a successful midair catch, and the rest show how jamming calls foil the attempts. Credit: A.J. Corcoran et al./Science 2014.