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      Stroke frequency, but not swimming speed, is related to body size in free-ranging seabirds, pinnipeds and cetaceans

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          It is obvious, at least qualitatively, that small animals move their locomotory apparatus faster than large animals: small insects move their wings invisibly fast, while large birds flap their wings slowly. However, quantitative observations have been difficult to obtain from free-ranging swimming animals. We surveyed the swimming behaviour of animals ranging from 0.5 kg seabirds to 30 000 kg sperm whales using animal-borne accelerometers. Dominant stroke cycle frequencies of swimming specialist seabirds and marine mammals were proportional to mass −0.29 ( R 2=0.99, n=17 groups), while propulsive swimming speeds of 1–2 m s −1 were independent of body size. This scaling relationship, obtained from breath-hold divers expected to swim optimally to conserve oxygen, does not agree with recent theoretical predictions for optimal swimming. Seabirds that use their wings for both swimming and flying stroked at a lower frequency than other swimming specialists of the same size, suggesting a morphological trade-off with wing size and stroke frequency representing a compromise. In contrast, foot-propelled diving birds such as shags had similar stroke frequencies as other swimming specialists. These results suggest that muscle characteristics may constrain swimming during cruising travel, with convergence among diving specialists in the proportions and contraction rates of propulsive muscles.

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          A digital acoustic recording tag for measuring the response of wild marine mammals to sound

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            Flying and swimming animals cruise at a Strouhal number tuned for high power efficiency.

            Dimensionless numbers are important in biomechanics because their constancy can imply dynamic similarity between systems, despite possible differences in medium or scale. A dimensionless parameter that describes the tail or wing kinematics of swimming and flying animals is the Strouhal number, St = fA/U, which divides stroke frequency (f) and amplitude (A) by forward speed (U). St is known to govern a well-defined series of vortex growth and shedding regimes for airfoils undergoing pitching and heaving motions. Propulsive efficiency is high over a narrow range of St and usually peaks within the interval 0.2 < St < 0.4 (refs 3-8). Because natural selection is likely to tune animals for high propulsive efficiency, we expect it to constrain the range of St that animals use. This seems to be true for dolphins, sharks and bony fish, which swim at 0.2 < St < 0.4. Here we show that birds, bats and insects also converge on the same narrow range of St, but only when cruising. Tuning cruise kinematics to optimize St therefore seems to be a general principle of oscillatory lift-based propulsion.
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              Principles of Animal Locomotion

               R Alexander (2003)

                Author and article information

                Proc Biol Sci
                Proceedings of the Royal Society B: Biological Sciences
                The Royal Society (London )
                5 December 2006
                22 February 2007
                : 274
                : 1609
                : 471-477
                [1 ]simpleInternational Coastal Research Centre, Ocean Research Institute, The University of Tokyo 2-106-1 Akahama, Otsuchi, Iwate 028-1102, Japan
                [2 ]simpleGraduate School of Fisheries Sciences, Hokkaido University Minato-cho 3-1-1, Hakodate 041-8611, Japan
                [3 ]simpleNational Institute of Polar Research 1-9-10 Kaga, Itabashi, Tokyo 173-8515, Japan
                [4 ]simpleSea Mammal Research Unit, University of St Andrews Fife KY16 8LB, UK
                [5 ]simpleInstitute for East China Sea Research, Nagasaki University Taira-machi 1551-7, Nagasaki 851-2213, Japan
                [6 ]simpleCenter for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0204, USA
                [7 ]simpleCentre d'Ecologie et Physiologie Engergétiques, CNRS 23 rue Becquerel, 67087 Strasbourg Cédex, France
                [8 ]simpleNational Research Institute of Fisheries Engineering, Fisheries Research Agency Hasaki, Kamisu, Ibaraki 314-0408, Japan
                [9 ]simpleCenter for International Cooperation, Ocean Research Institute, The University of Tokyo 1-15-1 Minamidai, Nakano, Tokyo 164-8639, Japan
                [10 ]simpleTokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
                [11 ]simpleLong Marine Laboratory, Department of Ecology and Evolutionary Biology, University of California Santa Cruz, CA 95060, USA
                [12 ]simpleCentre d'Etudes Biologiques de Chizé-CNRS Villier en Bois, 79360 Beauvoir/Niort, France
                [13 ]simpleBritish Antarctic Survey, Natural Environment Research Council High Cross, Madingley Road, Cambridge CB3 0ET, UK
                [14 ]simpleBiology Department, Woods Hole Oceanographic Institution Woods Hole, MA 02543, USA
                Author notes
                [* ]Author for correspondence ( katsu@ )
                Copyright © 2006 The Royal Society

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Research Article

                Life sciences

                optimal, accelerometer, scaling, power spectral density, free-ranging, dive


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