Sensory escape from a predator–prey arms race: Low amplitude biosonar beats moth hearing

Abstract

Ultrasound-sensitive ears evolved in many nocturnal insects, including some moths, to detect bat echolocation calls and evade capture. Although there is evidence that some bats emit echolocation calls that are inconspicuous to eared moths, it is difficult to determine whether this was an adaptation to moth hearing or originally evolved for a different purpose. Here we present the first example of an echolocation counterstrategy to overcome prey hearing at the cost of reduced detection distance, providing an example of a predator outcompeting its prey despite the life-dinner-principle. Aerial-hawking bats generally emit high-amplitude echolocation calls to maximize detection range. Using comparative acoustic flight-path tracking of free-flying bats, we show that the barbastelle, Barbastella barbastellus, emits calls that are 10 to 100 times lower in amplitude than those of other aerial hawking bats. Model calculations demonstrate that only bats emitting such low-amplitude calls hear moth echoes before their calls are conspicuous to moths. We confirm that the barbastelle remains undetected by moths until close and preys mainly on eared moths, using moth neurophysiology in the field and fecal DNA analysis. This adaptive stealth echolocation allows the barbastelle to access food resources that are difficult to catch for high-intensity bats.