Bats Yell, Too

Imagine you’re in a noisy restaurant, trying and failing to place an order. “IT’S VERY LOUD IN HERE!” you shout to your server, who shrugs. Now imagine that same conversation conducted super-fast, at a pitch so squeaky-high that you can’t even hear it. Researchers say bats are incredibly speedy at recognizing when they need to start shouting. A report on the bats’ raised voices is forthcoming in the Proceedings of the National Academy of Sciences.

Humans, bats, and other animals often start our conversations at one volume, then adjust as necessary. Study co-author Ninad Kothari of Johns Hopkins University says this seemingly simple action, called the Lombard effect, has proved complicated to understand.

“Scientists have been wondering for a century—could there be a common auditory process to explain how this phenomenon happens in fish to frogs to birds to humans, species with wildly different hearing systems?” Kothari said in a statement.

Previous studies had found that the Lombard effect takes about 150 milliseconds for birds and bats, and between 150 and 175 milliseconds for people.

Human listening, like human speech, can be messy, slow, and difficult to study. But bats’ echolocation squeaks and chirps are quick and precise, which makes them excellent scientific subjects.

Kothari and his colleagues Jinhong Luo and Cynthia Moss, also of Johns Hopkins, trained big brown bats (Eptesicus fuscus) to sit calmly on little platforms surrounded by recording equipment. The researchers set up an automated pulley system that brought insects zooming toward the bats, then listened as the bats hunted, bouncing sound off the approaching meal. Sometimes they let the bats go about their business in silence; other hunting sessions were interrupted by bursts of loud white noise.

The results suggest that earlier speed estimates had been way, way off. Just 30 milliseconds after hearing white noise, the bats got louder. That’s a “remarkably short” reaction time, the authors say.

“Typically, we breathe every three to five seconds, our heart beats once per second, and eye blinking takes one-third of a second,” Luo said in the statement. “If we believe that eye blinking is fast, the speed at which an echolocating bat responds to ambient noise is truly shocking: 10 times faster than we blink our eyes.”

Not bad, bats. Not bad.