HAMILTON, J.L.; Brown University, Providence, RI: Three-dimensional kinematics of wing-propelled swimming of the Thick-billed murre (Uria lomvia)

Birds of the family Alcidae are capable of both aerial fight and wing-propelled diving. Previous qualitative descriptions of their wing movements while swimming range from underwater “flight” to “rowing”. My study investigates the three-dimensional kinematics of swimming in the Thick-billed murre (Uria lomvia). Two murres were trained to swim against currents ranging from 0.1 to 0.5 m/s in a variable speed flume. Markers were fixed to the elbow and wrist joints, cranial and caudal ends of the sternum, shoulder, alula, wing tip and the trailing edge of the wing directly behind the wrist. Two digital video cameras (250 Hz) were positioned laterally and ventrally. Peak Performance Software was used to digitize each point in both camera views and calculate three-dimensional coordinates. At all current speeds, the average body velocity ranges from 1.5 to 1.9 m/s, with the peak velocity occurring at the end of downstroke. Maximum forward acceleration (6-11 m/s²) occurs at mid-downstroke. During upstroke, the bird decelerates initially, but accelerates slightly during mid-upstroke before decelerating again at the end of upstroke, suggesting an active upstroke. Body velocity decreases during upstroke; however, coincident with the slight forward acceleration at mid-upstroke, it becomes constant, occasionally increasing briefly, before decreasing near the end of upstroke. The elbow and wrist joints are held partially flexed throughout the stroke cycle, but do not show synchronous patterns of flexion/extension. During downstroke, the elbow undergoes flexion, whereas the wrist flexes early but then extends. During upstroke, the elbow extends but the wrist flexes. These asynchronous patterns contrast with the in-phase joint changes seen in aerial flight. The Wyss Foundation funded this work.