Penguin Swimming. II. Energetics and Behavior

Abstract

Oxygen consumption ($\dot{V}O_{2}$) Of the Humboldt penguin Spheniscus humboldti was measured during swimming over the range 0.23-1.26 m s⁻¹. The fraction of time spent swimming submerged and on the surface was recorded simultaneously with VO₂. The power output ($P_{o}$), computed from surface:submerged swimming ratios and drag data, and the power input ($P_{i}$), from $\dot{V}O_{2}$, were determined for each speed. Overall energetic efficiency ($\eta_{o}$), the ratio $P_{o}$ :$P_{i}$, increased with swimming speed ($U_{b}$) as $\eta_{o} = 0.103U_{b}^{2.8}$ ($U_{b} = m s^{-1}$) with a maximum value of 0.192. The maximum propulsion efficiency ($\eta_{p}$), the ratio of $P_{o}$ :$P_{i}-less-maintenance-metabolism$, was 0.247. By changing from surface to submerged swimming as $U_{b}$ increases, the cost of transport remains constant at 13.4 J (kg.m)⁻¹ for $U_{b} = 0.5-1.26 m s^{-1}$. Increasing speeds without increasing transport costs enables the birds to reduce transit time to foraging locations without increasing energy expenditure, a distinct benefit when raising chicks on shore.