Sonar sound groups and increased terminal buzz duration reflect task complexity in hunting bats.

Katrine Hulgard,John M. Ratcliffe

doi:10.1038/srep21500

Katrine Hulgard, John M. Ratcliffe

Open Access

https://doi.org/10.1038/srep21500

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Abstract

More difficult tasks are generally regarded as such because they demand greater attention. Echolocators provide rare insight into this relationship because biosonar signals can be monitored. Here we show that bats produce longer terminal buzzes and more sonar sound groups during their approach to prey under presumably more difficult conditions. Specifically, we found Daubenton’s bats, Myotis daubentonii, produced longer buzzes when aerial-hawking versus water-trawling prey, but that bats taking revolving air- and water-borne prey produced more sonar sound groups than did the bats when taking stationary prey. Buzz duration and sonar sound groups have been suggested to be independent means by which bats attend to would-be targets and other objects of interest. We suggest that for attacking bats both should be considered as indicators of task difficulty and that the buzz is, essentially, an extended sonar sound group.

Highlights

More difficult tasks are generally regarded as such because they demand greater attention
We found that the time elapsed over the course of the entire attack sequence was significantly longer for the moving, airborne target category than the two experimental water categories, which did not differ from one another in this respect (ANOVA: F5,16 = 28.2, P < 0.0001, Tukey HSD post-hoc comparisons; Fig. 1B)
We compared this direct line distance to the estimated distance travelled and found that the more circuitous flight paths taken by bats when tracking and intercepting moving airborne prey compared to stationary or water-borne prey accounted for this discrepancy (Fig. 3)

Summary

Introduction

More difficult tasks are generally regarded as such because they demand greater attention. We show that bats produce longer terminal buzzes and more sonar sound groups during their approach to prey under presumably more difficult conditions. For humans and other animals, demands on sensorimotor integration and task complexity are generally positively related[1,2,3,4] Quantifying this relationship, with respect to attention, is made difficult because available environmental information and sensory system activity are not monitored in freely moving individuals[1,2,4]. In buzz II, bats drop their echolocation call peak frequency by roughly an octave, relative to the PF of the search phase calls, and produce calls at rates > 160 calls/s9 This combination of lower call PF and extremely fast call emission rate broadens the bat’s sonar beam and maximizes auditory scene updates, respectively. We tested the hypothesis that the duration of the buzz would change according to the strategy (hawking versus trawling) and degree of difficulty of the task (moving versus stationary target)

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