Strouhal number for flying and swimming in rhinoceros auklets Cerorhinca monocerata. (23rd March 2015)

• Record Type: Journal Article
• Authors: Kikuchi, Dale M.; Watanuki, Yutaka; Sato, Nobuhiko; Hoshina, Kenji; Takahashi, Akinori; Watanabe, Yuuki Y.
• Is Part Of: Journal of avian biology. Volume 46:Number 4(2015:Jul.)
• Page Start: 406
• Page End: 411
• Publication Date: 2015-03-23
• Subjects: Ornithology -- Periodicals; Ornithology -- Scandinavia -- Periodicals; 598
• DOI: 10.1111/jav.00642
• Languages: English
• ISSNs: 0908-8857

Abstract

<abstract abstract-type="main" xml:lang="en"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Alcids propel themselves by flapping wings in air and water that have vastly different densities. We hypothesized that alcids change wing kinematics and maintain Strouhal numbers (<italic>St</italic> = <italic>fA</italic>/<italic>U</italic>, where <italic>f</italic> is wingbeat frequency, <italic>A</italic> is the wingbeat amplitude, and <italic>U</italic> is forward speed) within a certain range, to achieve efficient locomotion during both flying and swimming. We used acceleration and GPS loggers to measure the wingbeat frequency and forward speed of free‐ranging rhinoceros auklets <italic>Cerorhinca monocerata</italic> during both flying and swimming. We also measured wingbeat amplitude from video footage taken in the wild. On average, wingbeat frequency, forward speed, and wingbeat amplitude were 8.9 Hz, 15.3 m s<sup>−1</sup>, and 0.39 m, respectively, during flying, and 2.6 Hz, 1.3 m s<sup>−1</sup>, and 0.18 m, respectively, during swimming. The smaller wingbeat amplitude during swimming was achieved by partially folding the wings, while maintaining the dorso‐ventral wingbeat angle. Mean <italic>St</italic> was 0.23 during flying and 0.36 during swimming. The higher <italic>St</italic> value for swimming might be related to the higher thrust force required for propulsion in water. Our results suggest that rhinoceros auklets maintain <italic>St</italic> for both flying and swimming within the range (0.2–0.4) that propulsive efficiency is known to be high and <italic>St</italic> in both flying specialists and swimming specialists are known to converge.</p> </abstract>