The Research Saga Continues

During my junior year, Dr. Frank Fish offered me the opportunity to work on a research project studying the locomotion of eider ducks (Somateria mollissima) at Shoals Marine Laboratory. The project involved locating flocks of the birds swimming at the surface of the water and driving near them with an inflatable boat to provoke an escape response. Video analysis of these escape responses revealed two distinct locomotory patterns: 1) rapidly beating the wings against the water to produce thrust and hydroplane along the surface (steaming) and 2) lifting the body out of the water and “running” along the surface while flapping the wings (paddle-assisted flying). Out study was the first to describe these behaviors for the eider duck and the first to give a full biomechanical definition for each (Gough et al., 2015).

Diagram of the divergent and transverse waves produced by a duck as it moves at the water surface from dorsal (top) and lateral (bottom) views. The maximum waterline length (Lw) represents the length of the duck in contact with the water, from the base of the neck to the base of the tail. The wavelength (λ) of the surface wave increases as the duck builds speed. The point where the wavelength equals the waterline length is the hull speed. At the hull speed, the duck is effectively trapped in a wave trough, limiting surface swimming speed. In the lateral views, the lines in the wake represent the bow wave (solid curved line) relative to the undisturbed water line (solid horizontal line). Modified from Marchaj (1964).

Comparison of swimming performance for species swimming at the water surface. Common eiders are shown as a red point. Hull speed occurs at a Froude number of 0.4–0.45; below this range, the swimmer acts like a displacement hull, while a Froude number of 0.6–1.0 is considered to be semi-planing as the body is supported by both hydrodynamic and hydrostatic lift forces. Above a Froude number of 1.0, the body is supported solely by hydrodynamic lift and hydroplanes along the surface. Modified from Aigeldinger and Fish (1995).