Just as conversationalists at a loud cocktail party may raise their voices to be heard over the din, so do echolocating bats, according to a new study released Monday by the Proceedings of the National Academy of Sciences.
The effect is known as the Lombard effect, and it’s found in a wide range of chattering and chirping critters, from zebra finches to marmosets to humans. Often the effect registers not as turning up the volume (an increase in the sound wave’s amplitude), but in raising the pitch of one’s voice (a rise in frequency).
For this study, researchers from UCLA and Northeast Normal University in Jilin tested the reactions of three horseshoe bats collected from China. Bats make excellent test subjects: The nocturnal mammals have a fine-tuned sense of hearing and use echolocation to navigate in the dark.
Bats can hear (and use) a wide range of frequencies, stretching 100 Hz, but they have a particular resting frequency that they use when perched. The researchers introduced back noise above, below and right on top of that resting frequency, and recorded more than 83,000 echolocation calls to see how the bats reacted.