Data from: Inconspicuous echolocation in hoary bats (Lasiurus cinereus)

Echolocation allows bats to occupy diverse nocturnal niches. Bats almost
always use echolocation, even when other sensory stimuli are available to
guide navigation. Here, using arrays of calibrated infrared cameras and
ultrasonic microphones, we demonstrate that hoary bats (Lasiurus cinereus)
use previously unknown echolocation behaviors that challenge our current
understanding of echolocation. We describe a novel call type (“micro”
calls) that has three orders of magnitude less sound energy than other bat
calls used in open habitats. We also document bats flying close to
microphones (< 3 m) without producing detectable echolocation
calls. Acoustic modeling indicates that bats are not producing calls that
exceed 70-75 dB at 0.1 m, a level that would have little or no known use
for a bat flying in the open at speeds exceeding 7 m s-1. This indicates
that hoary bats sometimes fly without echolocation. We speculate that bats
reduce echolocation output to avoid eavesdropping by conspecifics during
the mating season. These findings might partly explain why tens of
thousands of hoary bats are killed at wind turbines each year. They also
challenge the long-standing assumption that bats—model organisms for
sensory specialization—are reliant on sonar for nocturnal navigation.