Estimates of the water and sodium fluxes of unrestrained Weddell seal pups were derived from the turnover of tritiated water and 22sodium chloride throughout the nursing period. Milk intake was calculated from water influx. There was a strong correlation between daily body weight gain in pups (x̄= 1·98 ± 0·44 kg/d) and daily weight loss by dams (x̄= 4·55±1·24 kg/d; r= 0·85, p <0·001). The maximum weight loss recorded was 249 kg over 38 days. This considerable drain on the dams' energy reserves amounts to a loss of almost 60 % of the female's body weight after parturition. Mean total body water of pups decreased from 72·5 % at birth to 48·6 % at day 40 of lactation. Total milk consumption was positively correlated with body weight gain by pups (r= 0·87, p < 0.001), with daily milk intake ranging from 2·76 to 5·46 1/day (x̄= 3.54 ± 0·87 1/d). The pups gained 0·51 ± 0·08 kg body weight for each litre of milk consumed, and the efficiency of conversion of milk energy to stored energy was 52·1 ± 7·7 %. Sodium influx rates averaged 2±24 · 0±41 mmol/kg. day. Approximately 70% of sodium intake was derived from milk, with the remainder coming from the ingestion of small amounts of sea water. The high energy content of the milk (20·8 MJ/kg) and reduced milk yield (relative to body weight) means that pups can consume sufficient energy for rapid growth with comparatively brief nursing periods and short lactational duration. The relatively longer duration of lactation in the Weddell seal, during which the dams and pups engage in extensive swimming activities, has resulted in: (a) reduced daily energy intake by pups, and (b) increased percentage weight loss by dams compared to other phocids.

The field metabolic rates (FMR) and water fluxes of Varanus scalaris were measured during the wet and dry seasons by the doubly‐labelled water technique. Seasonal measurements of standard (night‐time) metabolism (SMR) and resting (daytime) metabolism (RMR) were made in the laboratory at 18, 24, 30 and 36°C, and maximal oxygen consumption was measured at 36°C on a motorized treadmill. This population was active throughout the year. In the wet season, the mean FMR was 7.8 kJ day−1 (128.0 kJkg−1 day−1; mean mass = 66.4 g, n= 13), and during the dry season the mean was 5.0 kJ day−1 (67.6 kJ kg−1 day−1; mean mass = 77.4 g, n= 17). The mean water flux rates for these animals were 3.6 and 1.2 ml day−1, respectively (60.4 and 16.6 ml kg−1 day−1). The seasonal means of FMR and water flux were significantly different by ANCOVA (P < 0.0001). Measurements of SMR and RMR were significantly higher in the wet season (ANCOVA: P < 0.0001), but we found no difference in the maximal oxygen consumption between seasons (ANCOVA: P= 0.6). The maximal oxygen consumption of the lizards on the treadmill (2.9 ml min−1= 1.8 ml g−1 h−1), mean mass = 97.4 g, n= 16) was 20 times that of the SMR at the same temperature during the dry season, and 11 times that of the SMR during the wet season. The seasonal differences in FMR were attributable to: changes in SMR (12.2%) and RMR (16.4%); differences in night‐time body temperatures (11.3) and daytime body temperatures (16.4%); and activity (broadly defined to include locomotion, digestion, and reproductive costs (43.7%).

This study examines the annual energetics of a small folivorous marsupial, Pseudocheirus peregrinus. Particular attention was given to the energy and time allocated to reproduction by the females. Daily energy expenditure was measured directly using the doubly labelled water technique. Energy transferred to the young via the milk was estimated from information on milk composition and production. There was no significant seasonal variation in the energy expenditure or water influx of males or females. The mean daily energy expenditure of a 1-kg non-lactating adult ringtail possum was 615 kJ day or 2.2 times standard metabolic rate. Females showed significant changes in daily energy expenditure according to their reproductive status. Without the burden of lactation the total annual energy expenditure of an adult female was estimated as 212.4 MJ kg year. The total annual energy expenditure of a female rearing two young was 247.5 MJ kg year, with the late stage of lactation constituting the most energetically expensive period accounting for 30% of the total yearly energy expenditure during 24% of the time. Total metabolisable energy allocation during reproduction (22 MJ kg) was similar to estimates available for other herbivores, although, the peak metabolisable energy allocation during lactation (759 kJ day) was lower than values available for other herbivores. The total energy requirement for reproduction (metabolisable energy plus potential energy exported to young via milk) suggests that the ringtail possum also has a relatively low overall energy investment in reproduction. It is suggested that the lactational strategy of the ringtail possum has been selected in order to spread the energy demands of reproduction over time due to constraints on the rate of energy intake imposed by a leaf diet and/or to prolong the mother-young bond. The strategies a female ringtail possum may employ to achieve energy balance when faced with the energy demands of reproduction are discussed.

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The food and energy requirements of breeding gentoo penguins (Pygoscelis papua) were studied at Heard and Macquaric Islands by means of isotope turnover techniques. The food consumption rates of chicks were measured at various stages of growth, providing estimates of the total food provided by adults to rear a chick to fledging. The energy expenditures of attending adults were also measured at different stages of chick‐rearing, allowing the total energy costs associated with breeding to be established for a pair of adults and at the population level on both islands. We estimate the total annual energy budget of a 6·2 kg breeding gentoo penguin to be 1517 MJ which is equivalent to the consumption of 292 kg prey.