Strouhal number for flying and swimming in rhinoceros auklets Cerorhinca monocerata

Abstract

Alcids propel themselves by fl apping wings in air and water that have vastly diff erent densities. We hypothesized that alcids change wing kinematics and maintain Strouhal numbers ( St ϭ fA / U , where f is wingbeat frequency, A is the wingbeat amplitude, and U is forward speed) within a certain range, to achieve effi cient locomotion during both fl ying and swimming. We used acceleration and GPS loggers to measure the wingbeat frequency and forward speed of free-ranging rhinoceros auklets Cerorhinca monocerata during both fl ying 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 -1 , and 0.39 m, respectively, during fl ying, and 2.6 Hz, 1.3 m s -1 , and 0.18 m, respectively, during swimming. Th e smaller wingbeat amplitude during swimming was achieved by partially folding the wings, while maintaining the dorso-ventral wingbeat angle. Mean St was 0.23 during fl ying and 0.36 during swimming. Th e higher St value for swimming might be related to the higher thrust force required for propulsion in water. Our results suggest that rhinoceros auklets maintain St for both fl ying and swimming within the range (0.2 -0.4) that propulsive effi ciency is known to be high and St in both fl ying specialists and swimming specialists are known to converge.

Wing musculature reconstruction in extinct flightless auks (PinguinusandMancalla) reveals incomplete convergence with penguins (Spheniscidae) due to differing ancestral states

“…Unlike in aerial flight, additional wing area provided by a large propatagium would not be beneficial, and could even be detrimental, as water poses substantially more drag and resistance to moving wings than air, and thrust production in water is far more important than lift production (Rayner 1988). This expectation is supported by behavioral observations in extant volant auks, where the wings are seen to be kept in a partly folded position during aquatic flight, yielding smaller effective wing area than in the fully extended position (Stettenheim 1959;Spring 1971;Rayner 1995;Gaston and Jones 1998;Kikuchi et al 2015). As such, both the elongated crista deltopectoralis and attachment site for the ligg.…”

Feather corticosterone reveals stress associated with dietary changes in a breeding seabird

“…Loggers recorded data for one or two days and were deployed during a one‐week period midway through the breeding season (for details see Kikuchi et al. ).…”

“…Birds were outfitted with accelerometers (ORI-D3GT: /12 9 45 mm, 9 g, Little Leonardo Corp., Tokyo, Japan) that also recorded temperature and diving depth. Loggers recorded data for one or two days and were deployed during a one-week period midway through the breeding season (for details see Kikuchi et al 2015).…”

Upstroke-based acceleration and head stabilization are the norm for the wing-propelled swimming of alcid seabirds

“…The impressive diving capabilities of alcids have motivated multiple, independent studies on the biomechanics of alcid swimming and diving (Hamilton, 2006;Johansson and Aldrin, 2002;Kikuchi et al, 2015;Lovvorn et al, 2004;Watanuki and Sato, 2008;Watanuki et al, 2003Watanuki et al, , 2006, with one key focus being to compare stroke-acceleration patterns of swimming alcids with those of penguins.…”