HAMILTON, J.L.; Brown University, Providence, RI: Surface descent in Thick-billed murres (Uria lomvia): Are wings enough?

Thick-billed murres (Uria lomvia; Family Alcidae) are able to dive to depths exceeding 200 meters. Murres are positively buoyant and, thus, must overcome their own buoyancy when diving. My study investigates how murres use their limbs as they descend into the water column from the surface. The movements of the wings and feet during the first two wingbeats of diving in a variable-speed flume were recorded using high-speed video (250-500 fps). Kinematic parameters investigated include whole animal velocity and acceleration, body dive angle, wingbeat amplitude, and velocity of the wing relative to the body. Synchronous foot propulsion during the downstroke phase of the first wingbeat results in a peak forward acceleration during downstroke. Foot propulsion may accompany the second downstroke as well. If so, peak acceleration equals or exceeds that of the first downstroke. If the feet do not contribute to propulsion during the second downstroke, peak acceleration is approximately 50% of the first. The duration of downstroke and upstroke were equal for the two wingbeats, but the amplitude of the first wingbeat was 25% larger than the second. During downstroke, the wing moves backward relative to the body, suggestive of drag-based thrust during the initial part of the dive. Thus, both the wings and the feet contribute to the propulsion required to overcome buoyancy during the surface descent of the Thick-billed murre. The Wyss Foundation funded this work.