Energy Utilization by Free‐Ranging Jackass Penguins, Spheniscus Demersus

Rates of CO 2 production by breeding Jackass Penguins (means 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 calculated the energetic costs of swimming. Field metabolic rates (as CO 2 production) averaged 0.991 mL°g — 1 °h — 1 , or (in energy units) 3890 kJ°penguin — 1°2 d — 1. Energy expenditures were 1.7 times the standard metabolic rate (SMR) while brooding, 6.6 ° SMR while foraging, 9.8°SMR while swimming underwater, and 2°6 ° SMR integrated over a 2—d period. Penguins spent °48% 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 °758 g°penguin — 1 2 d — 1 for adults brooding small chicks, and °75 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 ° 10 7 kg of fish per year, of which °80% or 1.77 ° 10 7 kg would be Cape anchovies. This is °8% of the average commercial anchovy catch in that area.