Such excellent performance is realized by flapping-wing propulsion adapted to the physical properties of water. For example, field studies have shown that the average foraging speed of gentoo penguins ( Pygoscelis papua) is 2.3 m s −1 ( Sato et al., 2007), that Fiordland penguins ( Eudyptes pachyrhynchus) swim 80 km per day ( Mattern et al., 2018) and that the diving depth of emperor penguins ( Aptenodytes forsteri) reaches 564 m ( Wienecke et al., 2007). Their excellent swimming ability includes high-speed foraging, long migration and deep diving. Our results unveil a detailed mechanism of lift-based propulsion in penguins and underscore the importance of wing bending.Īmong the wing-propelled diving birds, penguins (Spheniscidae) are considered to be the most specialized for underwater swimming because they are free from the constraints of aerial flight ( Elliott et al., 2013 Storer, 1960). In addition, the propulsive efficiency for the original wing was estimated to be 1.8 times higher than that for the flat wing. Consequently, the calculated stroke-averaged thrust was larger for the original wing than for the flat wing during the upstroke. The motion analysis of the two wing models revealed that considerable bending occurred in the original wing, which reduced its angle of attack during the upstroke in particular. The resultant body trajectory showed that the penguin accelerated forward during both upstroke and downstroke. Using these coefficients, the thrust force during flapping was calculated in a quasi-steady manner, where the following two wing models were considered: (1) an ‘original’ wing model reconstructed from 3D motion analysis including bending deformation and (2) a ‘flat’ wing model obtained by flattening the original wing model. We also conducted a series of water tunnel experiments with a 3D printed rigid wing to obtain lift and drag coefficients in the gliding configuration.
In this study, we recorded the forward and horizontal swimming of gentoo penguins ( Pygoscelis papua) at an aquarium with multiple underwater action cameras and then performed a 3D motion analysis. Although previous motion analyses revealed their basic swimming characteristics, the details of the 3D wing kinematics, wing deformation and thrust generation mechanism of penguins are still largely unknown. Penguins are adapted to underwater life and have excellent swimming abilities.
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