Perceptual Modalities Guiding Bat Flight in a Native Habitat

Abstract

Flying animals accomplish high-speed navigation through fields of obstacles using a suite of sensory modalities that blend spatial memory with input from vision, tactile sensing, and, in the case of most bats and some other animals, echolocation. Although a good deal of previous research has been focused on the role of individual modes of sensing in animal locomotion, our understanding of sensory integration and the interplay among modalities is still meager. To understand how bats integrate sensory input from echolocation, vision, and spatial memory, we conducted an experiment in which bats flying in their natural habitat were challenged over the course of several evening emergences with a novel obstacle placed in their flight path. Our analysis of reconstructed flight data suggests that vision, echolocation, and spatial memory together with the possible exercise of an ability in using predictive navigation are mutually reinforcing aspects of a composite perceptual system that guides flight. Together with the recent development in robotics, our paper points to the possible interpretation that while each stream of sensory information plays an important role in bat navigation, it is the emergent effects of combining modalities that enable bats to fly through complex spaces.

Figure 1. Audio and video data are synchronized and then overlaid with the environment to study the variations of bat behavior spatially and temporally.

The flight corridor is about 7 meters long and 4 meters wide with Myotis velifer flying from the right (where their cave roost is located) to the left (towards their foraging area). A PVC pipe was placed in the middle of the flight corridor from day 2 to day 6. Three dimensional flight trajectories (colored curves are sample tracks from day 2) were then synchronized with bat calls (their locations are shown as red dots) during post-processing of data. –Photograph background by Z. Kong; three dimensional trajectories and overall image composition by S. Wang. The upper-right inset shows some reconstructed trajectories on day 2 where red triangles indicate the locations of hot-pads and red circle indicates the location of the hot-pad attached to the pole.

Figure 2. Histograms showing the effects of spatial memory on the flight behavior of bats.

The histograms of (a) mean call rate (in Hz), (b) mean speed (in meter per second) and (c) mean turning rate (in radian per second) are shown for days 1, 2, 4, 6, and 7. Black triangles mark key feature locations (e.g., tree branches). Black dots mark locations of the obstacle (its virtual locations on days 1 and 7 were shown for comparison). The evolution of (d) call rate and (e) speed is shown for the positions marked as black squares in (a,b). (f) shows the occupancy histograms of day 1 and day 7. The black dots mark the virtual locations of the pole.

Figure 3. Summary of the heading delay definition for a leader-follower bat pair.

(a) is a cartoon representation of a typical leader-follower pair with the red bat being the leader (bat i) and the yellow one being the follower (bat j). The arrows indicate the direction of motion at each time frame (with ∆ as the sampling time). For the bat pair (i, j), the heading correlation function is given by . The heading delay (a concept similar to the directional correlation delay introduced by Nagy et al.19) of the bat pair is then defined as that corresponds to the maximum value of C_ij(τ) as visualized in (b).

Figure 4. Heading alignment in leader-follower bat pairs is frequently too rapid to be explained by echoes returning from the followers’ vocalizations.

Horizontal axes denote follower bat heading delay values, indicating the time required for the follower to align with the leader. The green curves and blue curves show the PDFs (probability distribution function) of heading delays, and the CDF (cumulative distribution function) of heading delays, respectively. Vertical lines mark significant temporal values: red designates the end of the first call interval; black is one call interval time plus the auditory reaction time (90 ms), and the blue line is the average reaction time of maneuvering bats in a previous study (300 ms).