Like a football player running interference, a Mexican free-tailed bat (Tadarida brasiliensis) can block a competitor's ability to get a meal, a new study says for the first time.
Scientists observed bats using an acoustic call to jam another's echolocation—the process of bouncing sound waves off nearby objects to sense what's around them. (See National Geographic's best bat pictures.)
Many bats echolocate to zero in on prey, such as insects—and without it, hunting is nearly impossible.
The new research, published November 6 in Science, reveals that the Mexican free-tailed bat makes the interference call when another bat of the same species is closing in on dinner.
Aaron Corcoran, a biology postdoctoral student at the University of Maryland, discovered this behavior by accident.
He was studying how the Grote's tiger moth (Bertholdia trigona) jams the sonar of the big brown bat (Eptesicus fuscus) on the Arizona-New Mexico border when he noticed Mexican free-tailed bats flying high above, making their own calls.
As he reviewed the acoustic data back in the lab, Corcoran noticed that the call made by Mexican free-tailed bats was eerily similar to the series of ultra-fast clicking sounds the tiger moth used to block the big brown bats' sonar—and thus avoid becoming dinner. (See "'Whispering' Bat Evolved to Trick Prey.")
He came up with the hypothesis that the Mexican free-tailed bats were trying to block each other's hunting calls.
But, he said, "I had jamming signals on the brain, and so I needed to convince myself that this was true and I wasn't just imagining the similarity."
The Buzz on Bat Calls
To do this, Corcoran first had to rule out other potential explanations.
Back in the field, Corcoran and colleagues recorded several hours of wild Mexican free-tailed bat interactions using a high-speed camera and an array of microphones that could pinpoint the bats' locations.
Mexican free-tailed bats, which live in dense roosts, have rich social lives and make as many as 15 types of calls. Although Mexican free-tailed bats don't hunt as a group, they compete with each other as they hunt for insects each evening. (See "6 Bat Myths Busted: Are They Really Blind?")
When a Mexican free-tailed bat closes in on an insect, its echolocation pings become more and more frequent until the sounds coalesce into a distinctive call known as a feeding buzz.
According to Corcoran's recordings, a bat jammed another bat's sonar only when it was emitting the feeding buzz, which supported his initial hypothesis.
Corcoran's next step was to play back recordings of the jamming signal to see how it affected the behavior of Mexican free-tailed bats in the wild.
When he played the signal right as a bat was about to catch an insect, the bat was up to 85.9 percent less likely to catch its prey.
If Corcoran didn't play the jamming signal precisely as another bat homed in on an insect, or if he altered the pitch, it had no impact on ability to catch prey. (See "Climate Change Affects Ultrasonic Bat Signals for Better, Worse.")
Corcoran believes the jamming signals improve the sender's ability to catch its own meal, although he has yet to test this idea.
Masters of the Jam
The study team hasn't identified other bat species that use a jamming signal.
However, given the tremendous diversity of bats, Corcoran said it wouldn't be surprising if this signal has evolved in other species as well.
"I had no idea that such a behavior existed until now," said John Ratcliffe, a biologist at the University of Toronto who studies bat echolocation and wasn't involved in the new study. "It's absolutely fantastic work."
Ratcliffe noted that the bats' competition for the same food source provided "the perfect environment" for such a behavior to evolve.
"Mexican free-tailed bats," he said, "are masters of the jam."