Meeting Abstract
11-6 Friday, Jan. 4 09:15 – 09:30 The Comparative Biomechanics of Aerial and Aquatic Flight in Alcids LAPSANSKY, AB*; TOBALSKE, BW; University of Montana; University of Montana anthony.lapsansky@umontana.edu
Roughly 40 species of birds across five extant clades have co-opted their wings for use in underwater propulsion, here termed “aquatic flight”, while retaining their aerial flight. This group serves as an ideal case-study in evolution under distinct selective pressures, as water is 800X denser and 60X more viscous than air. Consider that the major component of force produced by a bird in aerial flight is oriented to counteract gravity. In contrast, buoyancy is the dominant force in aquatic flight at most depths. Thus, this dual-media strategy requires that the same bird produce forces in opposite directions with the same morphological structures. How aquatic flight is accomplished, and the potential tradeoffs of this strategy, are unclear. We recorded the kinematics of five species of alcids in water and air at the Alaska SeaLife Center and off the California coast. For underwater flights, we coupled this with qualitative analysis of the wake visualized using bubbles released from the plumage. In all species, we found that the aquatic downstroke produced lift that contributed to horizontal thrust and ‘weight-support’, as it does in aerial flight. The aquatic upstroke produces a strong downward-oriented force, counteracting buoyancy and the upward momentum of the downstroke. Thus, the upstroke has a unique function in aquatic flight. The upstroke generates circulation and ventrally-directed lift in select sequences and drag-based force in others. Further negative lift was apparent in underwater gliding sequences during which birds accelerated ventrally without wing movement. We also observed substantial feather deformation during underwater flight. We hypothesize that this is facilitated by a swept-wing posture, and that this deformation directs force production to increase hydrodynamic efficiency.
