Penguin Swimming. II. Energetics and Behavior

Oxygen consumption (V̇O₂) 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 (Pₒ), computed from surface:submerged swimming ratios and drag data, and the power input (Pᵢ), from V̇O₂, were determined for each speed. Overall energetic efficiency (ηₒ), the ratio Pₒ :Pᵢ, increased with swimming speed (Ub) as ηₒ = 0.103Ub2.8 (Ub = m s⁻¹) with a maximum value of 0.192. The maximum propulsion efficiency (ηₚ), the ratio of Pₒ :Pᵢ-less-maintenance-metabolism, was 0.247. By changing from surface to submerged swimming as Ub increases, the cost of transport remains constant at 13.4 J (kg.m)⁻¹ for Ub = 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.