title: Stroke and glide of wing-propelled divers: deep diving seabirds adjust surge frequency to buoyancy change with depth.
abstract: In order to increase locomotor efficiency, breath-holding divers are expected to adjust their forward thrusts in relation to changes of buoyancy with depth. Wing propulsion during deep diving by Brünnich's guillemots (Uria lomvia) was measured in the wild by high-speed (32 Hz) sampling of surge (tail-to-head) and heave (ventral-to-dorsal) accelerations with bird-borne data loggers. At the start of descent, the birds produced frequent surges (3.2 Hz) during both the upstroke and the downstroke against buoyancy to attain a mean speed of 1.2-1.8 m s(-1) that was close to the expected optimal swim speed. As they descended deeper, the birds decreased the frequency of surges to 2.4 Hz, relaying only on the downstroke. During their ascent, they stopped stroking at 18 m depth, after which the swim speed increased to 2.3 m s(-1), possibly because of increasing buoyancy as air volumes expanded. This smooth change of surge frequency was achieved while maintaining a constant stroke duration (0.4-0.5 s), presumably allowing efficient muscle contraction.
authors.affiliation: Laboratory of Animal Ecology, Graduate School of Agriculture, Hokkaido University, Kita-ku, Sapporo 060-8589, Japan. ywata@res.agr.hokudai.ac.jp
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Watanuki
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Niizuma
authors.forename: Geir Wing
authors.initials: GW
authors.lastname: Gabrielsen
authors.forename: Katsufumi
authors.initials: K
authors.lastname: Sato
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Naito
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001717:Birds / Q000502:physiology*; D004242:Diving / Q000502:physiology*; D013550:Swimming; D013997:Time Factors; D014921:Wings, Animal / Q000502:physiology*