Dolphins Can Maintain Vigilant Behavior through Echolocation for 15 Days without Interruption or Cognitive Impairment

Brian K Branstetter,Sam H Ridgway,Elizabeth A Fletcher,James J Finneran,Brian C Weisman,Brock Fenton

doi:10.1371/journal.pone.0047478

Abstract

In dolphins, natural selection has developed unihemispheric sleep where alternating hemispheres of their brain stay awake. This allows dolphins to maintain consciousness in response to respiratory demands of the ocean. Unihemispheric sleep may also allow dolphins to maintain vigilant states over long periods of time. Because of the relatively poor visibility in the ocean, dolphins use echolocation to interrogate their environment. During echolocation, dolphin produce clicks and listen to returning echoes to determine the location and identity of objects. The extent to which individual dolphins are able to maintain continuous vigilance through this active sense is unknown. Here we show that dolphins may continuously echolocate and accurately report the presence of targets for at least 15 days without interruption. During a total of three sessions, each lasting five days, two dolphins maintained echolocation behaviors while successfully detecting and reporting targets. Overall performance was between 75 to 86% correct for one dolphin and 97 to 99% correct for a second dolphin. Both animals demonstrated diel patterns in echolocation behavior. A 15-day testing session with one dolphin resulted in near perfect performance with no significant decrement over time. Our results demonstrate that dolphins can continuously monitor their environment and maintain long-term vigilant behavior through echolocation.

Highlights

During echolocation, an animal produces a sound and listens to returning echoes to gain information about its environment
The echolocation signals of the bottlenose dolphin can be described as a series of broadband transient clicks, with peak frequencies typically between 40 and 120 kHz, durations as small as 40 msec, with a peak-to-peak sound pressure level (SPLp-p) often exceeding 200 dB re 1 mPa [6]
The study followed a protocol approved by the Institutional Animal Care and Use Committee of the Biosciences Division, Space and Naval Warfare Systems Center Pacific, and all applicable U.S Department of Defense guidelines for the care of laboratory animals

Summary

Introduction

An animal produces a sound and listens to returning echoes to gain information about its environment. The echolocation signals of the bottlenose dolphin can be described as a series of broadband transient clicks, with peak frequencies typically between 40 and 120 kHz, durations as small as 40 msec, with a peak-to-peak sound pressure level (SPLp-p) often exceeding 200 dB re 1 mPa [6]. These signals are projected forward in a tight beam [6] where the width and direction of the beam can be actively manipulated depending on target location and target acoustic properties [7,8]. Cooperative herding is mediated by monitoring prey and the position of group members through echolocation, which suggest dolphins can echolocate for at least most of the night [1]

Methods

Results

Conclusion