The Determination of Distance by Echolocating Bats

SUMMARY We investigated the echolocating bat's use of an acoustic landmark for orientation in a complex environment with no visual information. Three bats of the species Eptesicus fuscus were trained to fly through a hole in a mist net to receive a food reward on the other side. In all experiments, the vocal behavior of the bats was recorded simultaneously using a high-speed video recording system, allowing for a 3D reconstruction of the flight path. We ran three types of experiments, with different spatial relations between the landmark and net hole. In the first experiment, the bat's behavior was studied in test trials with the landmark placed 10 cm to the left of the net opening; between test trials, the positions of the net opening and landmark were moved, but the spatial relationship between the two remained fixed. With the landmark adjacent to the net opening, the bats quickly found the hole. In the second experiment, bats were tested in control trials in which the landmark was moved independently of the hole, breaking the established spatial relationship between the two. In control trials the bats repeatedly crashed into the net next to the landmark, and inspected the area around it. In the final experiment, the landmark was removed altogether from the set-up. Here the bats spent more time per trial searching for the net opening with an increased number of inspections as well as crashes into the net. However, over the course of a test day without the landmark, bats reduced the time spent per trial and focused inspections and crashes around the hole. The behavioral data show for the first time that the echolocating bat can learn to rely on an acoustic landmark to guide spatial orientation.

Section: Acoustic Behaviormentioning

confidence: 99%

Section: Sound Analysismentioning

confidence: 99%

Echolocating bats can use acoustic landmarks for spatial orientation

Jensen

Moss

Surlykke

2005

“…Bats reduce call duration to avoid pulse-echo overlap with nearby objects (Cahlander et al, 1964;Kalko and Schnitzler, 1989;Schnitzler et al, 1987), widen call bandwidth to better localize objects (Faure and Barclay, 1994;Hartley, 1992;Kalko and Schnitzler, 1993;Surlykke et al, 1993), reduce call intensity as they approach objects as a method for keeping target echo strength constant (Hartley, 1992;Hiryu et al, 2007), and decrease directionality to widen the field of view as they attack prey (Jakobsen and Surlykke, 2010). These adaptations occur as the bat adjusts the timing of sonar sounds, and may also be influenced by the temporal dynamics of respiration and flight kinematics.…”

Section: Introductionmentioning

confidence: 99%

Tight coordination of aerial flight maneuvers and sonar call production in insectivorous bats

Falk

Kasnadi

Moss

2015

Echolocating bats face the challenge of coordinating flight kinematics with the production of echolocation signals used to guide navigation. Previous studies of bat flight have focused on kinematics of fruit and nectar-feeding bats, often in wind tunnels with limited maneuvering, and without analysis of echolocation behavior. In this study, we engaged insectivorous big brown bats in a task requiring simultaneous turning and climbing flight, and used synchronized high-speed motion-tracking cameras and audio recordings to quantify the animals' coordination of wing kinematics and echolocation. Bats varied flight speed, turn rate, climb rate and wingbeat rate as they navigated around obstacles, and they adapted their sonar signals in patterning, duration and frequency in relation to the timing of flight maneuvers. We found that bats timed the emission of sonar calls with the upstroke phase of the wingbeat cycle in straight flight, and that this relationship changed when bats turned to navigate obstacles. We also characterized the unsteadiness of climbing and turning flight, as well as the relationship between speed and kinematic parameters. Adaptations in the bats' echolocation call frequency suggest changes in beam width and sonar field of view in relation to obstacles and flight behavior. By characterizing flight and sonar behaviors in an insectivorous bat species, we find evidence of exquisitely tight coordination of sensory and motor systems for obstacle navigation and insect capture.

“…Detecting prey, parsing the acoustic scene and localizing objects require sonar signals tailored to each task. Bats that emit short-frequency-modulated calls of low duty cycle to capture insects on the wing reduce the duration of calls in cluttered environments to minimize pulse-echo overlap (Cahlander et al, 1964;Kalko and Schnitzler, 1989;Schnitzler et al, 1987) and widen call bandwidth to increase information about object location (Faure and Barclay, 1994;Hartley, 1992;Jensen and Miller, 1999;Kalko and Schnitzler, 1993;Surlykke et al, 1993). These bats also adjust the interval between successive calls to receive echoes from relevant objects before producing the next call (Moss and Surlykke, 2001;Surlykke and Moss, 2000).…”

Section: Introductionmentioning

confidence: 99%

Bats coordinate sonar and flight behavior as they forage in open and cluttered environments

Falk

Jakobsen

Surlykke

et al. 2014

Echolocating bats use active sensing as they emit sounds and listen to the returning echoes to probe their environment for navigation, obstacle avoidance and pursuit of prey. The sensing behavior of bats includes the planning of 3D spatial trajectory paths, which are guided by echo information. In this study, we examined the relationship between active sonar sampling and flight motor output as bats changed environments from open space to an artificial forest in a laboratory flight room. Using high-speed video and audio recordings, we reconstructed and analyzed 3D flight trajectories, sonar beam aim and acoustic sonar emission patterns as the bats captured prey. We found that big brown bats adjusted their sonar call structure, temporal patterning and flight speed in response to environmental change. The sonar beam aim of the bats predicted the flight turn rate in both the open room and the forest. However, the relationship between sonar beam aim and turn rate changed in the forest during the final stage of prey pursuit, during which the bat made shallower turns. We found flight stereotypy developed over multiple days in the forest, but did not find evidence for a reduction in active sonar sampling with experience. The temporal patterning of sonar sound groups was related to path planning around obstacles in the forest. Together, these results contribute to our understanding of how bats coordinate echolocation and flight behavior to represent and navigate their environment.