Katsufumi Sato 1 , * , Yutaka Watanuki 2 , Akinori Takahashi 3 , Patrick J.O Miller 1 , 4 , Hideji Tanaka 2 , Ryo Kawabe 5 , Paul J Ponganis 6 , Yves Handrich 7 , Tomonari Akamatsu 8 , Yuuki Watanabe 9 , Yoko Mitani 10 , Daniel P Costa 11 , Charles-André Bost 12 , Kagari Aoki 9 , Masao Amano 1 , Phil Trathan 13 , Ari Shapiro 14 , Yasuhiko Naito 3
5 December 2006
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.