Bats produce sounds to navigate their surroundings in a process called echolocation. The problem is that sound does not travel very well through air. To overcome this barrier, bats produce very high-intensity sounds. In fact, some bats can even produce sounds that are around 137 decibels sound pressure level (dB SPL), which is near the range that can cause hearing damage in people. Just like people, bats call at higher intensities in noisier environments. The problem is that echolocation is a rather expensive process – metabolically speaking of course. Research has shown that the metabolism of small bats increases over 10 times when they are echolocating at rest although studies have suggested that vocalizations were energetically inexpensive during flight.
In a new study published in Nature Ecology & Evolution, researchers examined how much energy the Nathusius’ pipistrelles (Pipistrellus nathusii) bats use in creating vocalizations during flight in a wind tunnel. What the researchers found was that the metabolic energy required to vocalize in an enclosed wind tunnel at low intensities (i.e. less than 110 dB) was rather low, about 0.3-2.7% of the total metabolic power needed to fly. These findings were consistent with what other researchers had observed. Although echolocation at high intensities can help bats locate small insects in the distance, the cost of echolocation increased to 22% of the total metabolic power of flying when the bats flew in noisy conditions, akin to their natural environment. These findings show that it is indeed energetically expensive to call at high intensities while flying.
SE Currie, A Boonman, S Troxell, Y Yovel, CC Voigt. Echolocation at high intensity imposes metabolic costs on flying bats. Nature Ecology & Evolution. 2020. Doi: 10.1038/s41559-020-1249-8