Isotope turnover techniques were used to measure the metabolic and food consumption rates of free—living Little Penguins (Eudyptula minor) throughout the annual cycle in Bass Strait, Australia. Water and sodium flux rates were also measured, and all parameters showed significant seasonal differences. There were no differences between male and female adult Little Penguins in any of the parameters measured. The estimates of energy turnover were used to construct time/energy budgets for comparison with time/activity budgets. Although chick—rearing occupies only 16% of the annual time budget, this period is the most energetically expensive phase and accounts for 31% of the annual energy budget. The high energy costs of chick—rearing are particularly extreme toward the end of chick growth. At this time the daily rates of food consumption by attending adults exceed 60% of adult body mass. During the nobreeding season (winter) adult energy expenditure exceeds that acquired from feeding, and the birds lose body mass. The metabolic costs of pursuit diving appear to be similar to those associated with flapping flight. The total annual food requirements of Little Penguins in Bass Strait were estimated to be 37 000 Mg of food (fish, squid and krill). The penguins are most vulnerable to fluctuations in food availability, either as a result of natural perturbations or from commercial fishing activities, during the winter and during the chick—rearing phase of breeding. _kw Albatross Island, Tasmania