Development of diving capacity in emperor penguins

To compare the diving capacities of juvenile and adult emperor penguins Apt enodytes forsteri, and to determine the physiological variables underlying the diving ability of juveniles, we monitored diving activity in juvenile p enguins fitted with satellite-linked time/depth recorders and examined deve lopmental changes in body mass (M-b), hemoglobin concentration, myoglobin ( Mb) content and muscle citrate synthase and lactate dehydrogenase activitie s, Diving depth, diving duration and time-at-depth histograms were obtained from two fledged juveniles during the first 2.5 months after their departu re from the Cape Washingon colony in the Ross Sea, Antarctica. During this period, values of all three diving variables increased progressively. After 8-10 weeks at sea, 24-41% of transmitted maximum diving depths were betwee n 80 and 200 m, Although most dives lasted less than 2 min during the 2 mon th period, 8-25% of transmitted dives in the last 2 weeks lasted 2-4 min. T hese values are lower than those previously recorded in adults during forag ing trips. Of the physiological variables examined during chick and juvenil e development, only M-b and Mb content did not approach adult values, In bo th near-hedge chicks and juveniles, Mb was 50-60% of adult values and Mb co ntent was 24-31% of adult values. This suggests that the increase in diving capacity of juveniles at sea will be most dependent on changes in these fa ctors.