FIELD METABOLIC RATES OF BREEDING CHINSTRAP PENGUINS (PYGOSCELIS-ANTARCTICA) IN THE SOUTH SHETLAND

In a study using doubly labeled water, chinstrap penguins (mean body m ass 3.79 kg) caring for chicks expired on average 2.06-2.44 mL CO2 g(- 1) h(-1), depending on the equation used to calculate CO2 production f rom isotope turnover (the two-compartment and one-compartment models f or isotope dilution). This is equivalent to 4,720-5,537 kJ d(-1) and 4 .0-4.7 times the estimated basal metabolic rare. Energy use while guar ding small chicks on the nest was 0.58-0.69 mL CO2 g(-1) h(-1) (1,768- 2,124 kJ d(-1), or 1.5-1.8 times the basal metabolic rate), and it was 2.37-2.82 mL CO2 g(-1) h(-1) (5,421-6,423 kJ d(-1), or 4.6-5.4 times the basal metabolic rate) when foraging at sea. The field metabolic ra tes measured at sea are similar to those reported for Adelie penguins but higher than those in studies of other penguin species. Adult pengu ins expired 2.27-3.13 mL CO2 g(-1) h(-1) (5,O33-6,995 kJ d(-1)) while foraging for chicks in the guard stage and 2.45-2.60 mL CO2 g(-1) h(-1 ) (5,693-6,023 kJ d(-1)) while foraging for chicks in the creche stage . These values are not significantly different. Chicks of 40 d of age (3.34 kg) had field metabolic rates twice those measured in adults whi le on land guarding chicks but similar to those reported for chicks of other penguin species (1.11-1.30 mL CO2 g(-1) h(-1), or 2,280-2,695 k J d(-1)). We estimated that an adult in energy balance feeding grown c hicks would consume 1.67 kg of fresh krill daily to sustain its energy requirements, while one of its grown chicks would consume 0.53 kg of food daily. That would imply for a breeding adult a 32% increment abov e the foraging effort required to sustain its own needs.