Rapid shifts of sonar attention byPipistrellus abramusduring natural hunting for multiple prey

Abstract

Flight paths of echolocating Japanese house bats, Pipistrellus abramus, were tracked during insect hunting in a natural setting using a 32-microphone array. The array surrounded the foraging area, locating each bat, and determined the directional aim of the sonar beam. Successive interceptions, indicated by feeding "buzzes" and post-buzz pauses, occurred singly at intervals from over 20 s down to multiple interceptions at 2-3 s intervals. Bats flew on looping, curved paths. Turning radius tightened as rate of interceptions increased, keeping the bat in a smaller area of higher capture density. Broadcast beams shifted direction during search, often alternating between the direction of flight and another direction where, moments later, the next interception would occur. Broadcasts also shifted direction between the current target and the next target. Bats time-share biosonar attention between objects by alternating acoustic gaze. During search, most interpulse intervals (IPIs) were 70-120 ms, but bats interspersed long IPIs up to 200 ms when the rate of interception was low and flight paths followed broad curves. Mathematical modeling of search paths demonstrated that circular flight-paths with occasional long IPIs would be more effective for target search than either random, correlated random, or linear flights.

Echolocating bats use future-target information for optimal foraging

“…The Japanese pipistrelle bat (Pipistrellus abramus) increased its body weight by up to ∼20% during nightly foraging (20). We previously reported that P. abramus are capable of capturing prey every 2-3 s (15,21). In this study, we have shown that the bats select flight paths to efficiently capture consecutive prey items.…”

“…For multiple targets, it is beneficial for bats in the wild to distribute their sonar attention and flight attention among multiple targets and to plan the future flight path based on the next prey for effective foraging. On the other hand, pipistrelle bats in the wild alternately and rapidly shift their sonar attention (15,22). This fact suggests that bats process echo streams from multiple targets in a time-sharing manner and then select the optimal flight path to capture and hunt a lot of airborne insects.…”

“…The model assumes two prey items, because the microphone-array measurement showed that bats sometimes capture two prey items consecutively and rarely capture more than two insects within short time intervals. Bats changed their flight paths much more acrobatically in the horizontal plane than in the vertical plane during natural foraging (15,16). Thus, we separately model flight dynamics in the horizontal and vertical planes as follows:…”

“…When echolocating bats approach an airborne insect, the sonar attention directs toward the prey (12,13). During natural foraging, the sonar attention of bats alternately shifts from their flying direction to the side (15). Additionally the wild bats are capable of capturing two prey items within the short interval of 1 s (16).…”

Organization of projection from brainstem auditory nuclei to the inferior colliculus of Japanese house bat (Pipistrellus abramus)

“…Furthermore, by analyzing the distribution of retrogradely labeled cells inside the IC, we identified cell types that make long‐range intrinsic connection inside the IC. Although this species have been used frequently on biosonar studies (Fujioka et al., 2014; Sumiya, Fujioka, Motoi, Kondo, & Hiryu, 2017; Takahashi et al., 2014; Yamada, Hiryu, & Watanabe, 2016), the information about the organization of auditory pathways of this species has not been reported except for a single unit recording study from the IC (Goto, Hiryu, & Riquimaroux, 2010). Therefore, our study will give new neuroethological insights on biosonar.…”