Energy Utilization by Free-Ranging Jackass Penguins, Spheniscus Demersus

Rates of CO2 production by breeding Jackass Penguins (mean mass, 3170 g) were measured by using doubly labeled water. Time budgets were estimated from behavioral observations, and energy budgets were calculated for a typical 2-d period of 24 h sitting on a nest and 24 h off the nest (which includes 9 h foraging at sea). Distances traveled at sea were determined by using speed/ time meters harnessed to five birds containing doubly labeled water, and these measurements were used to calculate the energetic costs of swimming. Field metabolic rates (as CO2 production) averaged 0.991 mL'g'l h-', or (in energy units) 3890 kJ penguin-1 2 d-'. Energy expenditures were 1.7 times the standard metabolic rate (SMR) while brooding, 6.6 x SMR while foraging, 9.8 x SMR while swimming underwater, and 2.6 x SMR integrated over a 2-d period. Penguins spent z48% of their energy budget and 19% of their time budget to obtain food. Foraging efficiency (the metabolizable energy gained while foraging . the energy used during foraging) was 2.1 for birds with small chicks. Fresh mass consumption rates calculated on the basis of the chemical composition of Cape anchovy, Engraulis capensis, were Z758 g pen- guin-l 2 d-' for adults brooding small chicks, and 76 kg of anchovy per nest (2 adults, 2 chicks) over a 70-d nestling period. An adult penguin would need to capture ; 138 kg of fish per year. The 160,000 penguins using the South African fishing grounds would consume about 2.21 x 107 kg of fish per year, of which z80% or 1.77 x 107 kg would be Cape anchovies. This is z8% of the average commercial anchovy catch in that area.