Echolocation in Blainville’s beaked whales (Mesoplodon densirostris)
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Here we use sound and movement recording tags to study how deep-diving Blainville’s beaked whales (Mesoplodon densirostris) use echolocation to forage in their natural mesopelagic habitat. These whales ensonify thousands of organisms per dive but select only about 25 prey for capture. They negotiate their cluttered environment by radiating sound in a narrow 20° field of view which they sample with 1.5–3 clicks per metre travelled requiring only some 60 clicks to locate, select and approach each prey. Sampling rates do not appear to be defined by the range to individual targets, but rather by the movement of the predator. Whales sample faster when they encounter patches of prey allowing them to search new water volumes while turning rapidly to stay within a patch. This implies that the Griffin search–approach–capture model of biosonar foraging must be expanded to account for sampling behaviours adapted to the overall prey distribution. Beaked whales can classify prey at more than 15 m range adopting stereotyped motor patterns when approaching some prey. This long detection range relative to swimming speed facilitates a deliberate mode of sensory-motor operation in which prey and capture tactics can be selected to optimize energy returns during long breath-hold dives.
KeywordsEcholocation Biosonar Beaked whale Sampling rate Sensing
We thank L. Martin, M. Bayona, A. Schiavi, C. Reyes, A. Fais, J. Marrero, A. Escanez, M. Guerra and many others for dedicated help and hard work during field work off the coast of El Hierro. T. Hurst and A. Shorter provided skilled tag support. We thank P. Tyack, F. Jensen, M. Wahlberg, D. Wisniewska, K. Beedholm, and J. Mead for helpful discussions and/or comments on previous versions of the ms. Funding for Dtag development was provided by the Cecil H. and Ida M. Green Award and the US Office of Naval Research. Field work and initial analysis was funded by the Strategic Environmental Research and Development Program (SERDP) under program CS-1188, the National Oceanographic Partnership Program, and the Packard Foundation. Additional support was received from the Government of El Hierro; from the Spanish Ministry of Defence-Ministry of Environment-Canary Islands Government, and from Fundacion Biodiversidad (LIFE-INDEMARES). PTM was supported by frame grants from the National Danish Science Research Council, MJ by the Marine Alliance for Science and Technology, Scotland, and by a Marie Curie Career Integration Grant, NAS by project SOUNDMAR (Marie Curie 7th EU Frame Program) and PA by project CETOBAPH funded by the Spanish Ministerio de Economía y Competitividad. Research was conducted under a permit from the government of the Canary Islands to NAS. Finally we thank Dr. W. Hanke for hosting the stimulating workshop on marine mammal sensory systems that preceded this special volume.
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