Theresa L. Bucher

Energetics of Foraging in Breeding Adelie Penguins

We studied foraging energetics in Adelie Penguins (Pygoscelis adeliae) using doubly labeled water (DLW) and time-depth recorders (TDR). Measurements were made during three nesting stages: late incubation, the guard stage (when small chicks were con- tinuously guarded by at least one parent), and the subsequent creche stage (when large chicks were left unattended). Nest relief cycle times decreased from 229 h during incubation to 33.3 h during the creche stage, and the fraction of time birds spent swimming increased from 20.8% during incubation to 31.6% during the creche stage. The fraction of swim time spent in hunting dives and bottom time did not change significantly at different nesting stages. Field metabolic rates (FMR) were 2.73 x basal metabolic rate (BMR) during in- cubation, 3.03 x BMR during the guard stage, and 3.29 x BMR during the creche stage; due to high variance these values did not differ significantly. Estimated metabolic rate during swimming was 8.2 x BMR. Rates of prey capture (grams of krill per hour of swimming, per hour of hunting dives, and per hour of bottom time) did not change at different stages. Food provided to chicks was 20.9% (guard stage) to 23.3% (creche stage) of the food metabolized by adults. Our data suggest that (1) prey capture by Adelies is limited primarily by their ability to find krill swarms and not by limitations in harvest rates or energy efficiency after prey have been located, and (2) reproductive effort in Ad6lies does not require a large increase in either energy expenditures or foraging time.

Reproductive effort in Adélie penguins

SummaryWe estimated reproductive effort (energy expenditures for reproduction, as opposed to maintenance) in Adélie penguins breeding at Palmer Station, Antarctica. Data on body composition changes and metabolic rate were obtained using isotopic methods. Adelie breeding behavior consists of an initial courtship stage (during which both sexes fast), incubation, the ‘guard’ stage (when chicks are 1 to 18–28 days old), and the ‘creche’ stage (from the end of guarding until chicks are 28–45 days old). Both males and females lost considerable mass during the initial stages of the reproductive season, but males fasted longer and lost more mass. Mass losses of both sexes consisted of 66% depot fat and 34% lean tissue. Mass and body composition remained constant once birds resumed feeding. The metabolic expenditure for the foraging necessary to accumulate the mass lost while fasting — one component of reproductive effort —was about 63 MJ in males and 39 MJ in females. Field metabolic rates (FMR) were low during courtship and while incubating, increasing more than 2-fold when birds resumed foraging. Although mean FMR increased between incubation and the creche stage, differences between stages were small and not significant. We used FMR data and an energy balance model to estimate the cost of feeding chicks. Results suggest a maintenance FMR of about 2.7 × basal metabolism (BMR), increasing to 3.4–3.6 × BMR during the creche stage. The reproductive effort (as metabolic expenditures) associated with feeding chicks is 31 MJ (males) to 36 MJ (females). Cumulative reproductive effort is 94 MJ in males and 75 MJ in females, or 5.3–6.2% of the annual energy budget. The reproductive effort devoted to chick care does not appear to be constrained by physiological or time limitations. Instead, selection to reduce the risk of predation may prevent the evolution of increased parental care.

Parrot Eggs, Embryos, and Nestlings: Patterns and Energetics of Growth and Development

The Psittaciformes constitute a distinct and homogeneous order, members of which lay multiple egg clutches of relatively small eggs that have prolonged incubation periods. The chicks are altricial but nevertheless grow comparatively slowly. The contents of parrot eggs contain more solids (19.4%) than is typical for altricial or semialtricial species. The rate of embryonic oxygen consumption increases throughout incubation. The relative rate of increase in V̇o2 (percent per day) and the relative growth rate of the embryo decrease throughout incubation. The relative growth rate continues to decrease after hatching. In the six parrot species I studied, total embryonic energy metabolism is greater than predicted for altricial species owing to the prolonged incubation periods. Pre-pipping and hatching levels of oxygen consumption are lower than in the same size eggs of precocial species. In Agapornis roseicollis, mass-specific metabolism decreases through the first 15 days of incubation, then is relatively constant until immediately prior to hatching, increases sharply for about 4 days after hatching, becomes relatively constant for about 6 days, and then begins decreasing. This pattern reflects (1) changing maintenance costs due to increasing size and changes in maturational state and (2) changing growth costs which reflect the decreasing relative growth rate throughout the incubation and nestling periods.

Energy Metabolism and Nocturnal Hypothermia in Two Tropical Passerine Frugivores, Manacus vitellinus and Pipra mentalis

Oxygen consumption (V̇o2) and body temperature (Tb) were measured in Manacus vitellinus (mean mass, 15.5 g) and Pipra mentalis (mean mass, 12.3 g) on Barro Colorado Island, Panama. The two species had the same mean euthermic nocturnal Tb (37.9 C). During activity Tb sometimes reached 43 C. In both species, nocturnal basal metabolic rate (BMR) (41.69 cm³ O₂/h in M. vitellinus and 34.9 cm³ O₂/h in P. mentalis) was significantly less than predicted on the basis of mass. At night fasted birds frequently, and unfasted birds occasionally, became hypothermic, with Tb ranging between 27 and 36 C. Their Tb always remained several degrees above ambient temperature (Ta). The lowest Tb recorded was 26.8 C at a Ta of 14.6 C. Thermal conductance was the same in euthermic and hypothermic birds. Manakins save substantial amounts of energy by their nocturnal hypothermia. During a 12-h night a 14-g M. vitellinus maintaining a Tb of 27 C in a Ta of 22 C for 10 h would expend 6.4 kJ less than if it maintained its Tb at the mean euthermic nocturnal level. This represents a savings of 58%. The selective pressures that have favored nocturnal hypothermia in manakins have probably operated on other small tropical frugivorous birds. We predict that the main components of the metabolic pattern of manakins will also be found in other small tropical passerines with similar food habits.

Convection and thermoregulation in two Antarctic seabirds

Summary1.Metabolism and heat transfer were measured at different wind speeds (V) and ambient temperatures (Ta) in Adelie penguins (Pygoscelis adeliae) and blue-eyed shags (Phalacrocorax atriceps). Five age classes of penguins (adults, fledglings, and 1-, 2-, and 3-kg downy chicks) and three age classes of shags (adults and 2- and 3-kg chicks) were studied.2.In penguins, rates of oxygen consumption (

Ventilatory Oxygen Extraction in Relation to Ambient Temperature in Four Antarctic Seabirds

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Energy Metabolism and Patterns of Ventilation in Euthermic and Torpid Hummingbirds

) in the absence of forced convection increased with decreasingTa in downy chicks. The