Hunting bats adjust their echolocation to receive weak prey echoes for clutter reduction

Abstract

How animals extract information from their surroundings to guide motor patterns is central to their survival. Here, we use echo-recording tags to show how wild hunting bats adjust their sensory strategies to their prey and natural environment. When searching, bats maximize the chances of detecting small prey by using large sensory volumes. During prey pursuit, they trade spatial for temporal information by reducing sensory volumes while increasing update rate and redundancy of their sensory scenes. These adjustments lead to very weak prey echoes that bats protect from interference by segregating prey sensory streams from the background using a combination of fast-acting sensory and motor strategies. Counterintuitively, these weak sensory scenes allow bats to be efficient hunters close to background clutter broadening the niches available to hunt for insects.

Wild bats briefly decouple sound production from wingbeats to increase sensory flow during prey captures

“…The bats on average lost ∼2.5 g during the tagging period which is less than the average diurnal loss in body mass of 5.5 g during the one day spent at the station prior to release ( Table S1 ). In addition, these bats caught prey up to several hundred times per night with high success rates ( Table S2 ) suggesting that the tags did not have large effects on their ability to maneuver and catch prey as seen in previous studies ( Egert-Berg et al., 2018 ; Stidsholt et al., 2021 ).…”

“…We posit that this sparse sensory input might be the result of the (bio) physical constraints of a fast-flying echolocator in air that must couple call rates to a relatively low wingbeat rate to minimize the energy expenditure of echolocating. Despite this sparse sensory input and the very limited range of ultrasonic echolocation in air compared to ultrasound in water ( Madsen and Surlykke, 2013 ), their powerful calls enable the bats to still sample the same volume of air multiple times with successive calls ( Stidsholt et al., 2021 ) apparently providing sufficient sensory information to navigate and avoid obstacles. In concert with acute spatial memory in known habitats ( Genzel et al., 2018 ; Ratcliffe et al., 2005 ), this low information redundancy appears to be sufficient for routine navigation.…”

“…However, such slow sensory sampling for searching bats might result in lower prey detection rates and more reactive sensory motor operation in comparison to toothed whales ( Hein and McKinley, 2013 ). If so, we speculate that bats may compensate by capturing prey with high success rates ( Stidsholt et al., 2021 ) or by extracting more information from each sensory input than toothed whales due to the higher time bandwidth product of their echolocation calls ( Woodward, 1953 ). Such low sampling rates coupled to wingbeats may be speculated to explain the evolution of their complex calls and high-level auditory processing that potentially increase information extraction for each call-echo pair ( Corcoran and Moss, 2017 ).…”

“…The disproportionately low source levels of greater mouse-eared bats when emitting more than two calls per wingbeat may have several explanations. Bats may actively call faintly to reduce sensory volumes, thus simplifying their sensory scenes during prey tracking ( Stidsholt et al., 2021 ), or to maintain echo levels in a dynamic range suited for their hearing system at close ranges where they call at higher rates ( Denzinger and Schnitzler, 1998 ). Alternatively, the spreading of the calls over a larger proportion of the wingbeat cycle in the buzz may make sound production less efficient causing the 100x (−20 dB) reduction in summed energy output per wingbeat cycle ( Figure 2 D, pink).…”

Phylogenetic Patterns in Mouth Posture and Echolocation Emission Behavior of Phyllostomid Bats

“…One explanation would be that the two components could be emitted separately through nostrils and mouth, respectively. Synchronized high-speed video and audio recordings would be necessary to test this hypothesis and, combined with recent advances in bat tagging technology, might shed light on the functional significance of this pattern (Stidsholt et al, 2021).…”