Higher Daily Energy Expenditure Research Articles

Considerations for Protein Supplementation in Warfighters

Ingestion of dietary protein stimulates the synthesis of numerous body proteins. This effect is manifest via hyperaminoacidemia with insulin as a permissive factor. In a sedentary person in energy balance, it is possible to maintain nitrogen balance while consuming protein at an intake of 0.8 g protein · kg−1 · d−1. What is unclear is whether being in nitrogen balance is optimal for protein synthesis and not merely adequate and representative of adaptive strategies that could lead to accommodation in “stressed” physiological states. It is clear that being in negative energy balance results in reductions in lean mass and reduced rates of protein synthesis, which can be mitigated by consumption of higher (i.e., 2–3 times the RDA) dietary protein. That long-term practice of inadequate protein intake leads to reduced metabolic, physiological, and physical function provides the basic rationale for the consumption of more than merely adequate protein to prevent not only adaptation but accommodation. Warfighters engaged in combat have been shown to have high daily physical activity energy expenditure, engage in voluntary energy restriction, and are under high metabolic and mental stress. Thus, as a group warfighters would be at risk of consuming suboptimal protein intakes and therefore may benefit from higher amounts of dietary protein intake. Balanced against the potential risk of consuming higher protein, the scientific documentation for which is lacking, there is a strong rationale for the recommendation of higher protein intakes in warfighters who are engaged in field operations.

The role of physical activity and diet on bone mineral indices in young men: a cross-sectional study

BackgroundOsteoporotic fractures are a significant cause of morbidity and mortality, particularly in developed countries. Increasing peak bone mass in young people may be the most important primary prevention strategy to reduce the risk of osteoporosis. This study aimed to examine the relationship between dietary factors and physical activity on bone mineralization in young men.MethodsThirty-five healthy men aged 18–25 y had anthropometric measures, body composition, resting metabolic rate, blood pressure, blood lipids, food intake, physical activity and cardiorespiratory fitness assessed.ResultsParticipants who consumed more than 1000 mg/d of calcium were taller and had higher levels of whole body mineral content than participants who consumed less than 1000 mg/d of calcium. Similarly, participants who expended more than 20% of total daily energy engaged in moderate- to vigorous-intensity physical activity had higher cardiorespiratory fitness and higher levels of body mass adjusted bone mineral content than participants who did not meet this level of energy expenditure. There were no differences in blood pressure or blood lipids between participants in calcium or in physical activity energy expenditure categories.ConclusionsA high intake of dietary calcium and high daily energy expenditure engaged in moderate- to vigorous-intensity physical activity were positively associated with bone mineralization in young men, particularly in the lumbar region.

Impact of Physical Fitness and Daily Energy Expenditure on Sleep Efficiency in Young and Older Humans

Background: Physical activity is known to influence sleep efficiency. Relatively little is known about the relationship between physical activity and sleep efficiency in young and older humans and the impact of exercise training on sleep efficiency in healthy older individuals. Objectives: To determine the relationship between physical fitness and daily energy expenditure with sleep efficiency in young and older subjects, and assess the effect of 12-month exercise training on sleep efficiency in healthy older participants. Methods: The relationship between physical fitness (maximal cycling test) and daily energy expenditure (accelerometry) with sleep efficiency (accelerometry) was examined cross-sectionally in 12 healthy young adults (27 ± 5 years) and 21 healthy older participants (69 ± 3 years). Subsequently, the effect of 12-month exercise training (n = 11) or control period (n = 10) on sleep efficiency in older participants was examined using a randomized controlled trial. Results: Daily energy expenditure and sleep efficiency did not differ between young and older subjects. A significant correlation was found between energy expenditure and sleep efficiency (r = 0.627, p = 0.029) in young adults, but not in older participants (r = –0.158, p = 0.49). Physical fitness did not correlate with sleep efficiency in either group. Exercise training significantly improved physical fitness (15.0%, p < 0.001), but failed to alter sleep characteristics such as sleep efficiency, sleep onset latency and awakenings. Conclusions: We found that young adults with higher daily energy expenditure have greater sleep efficiency, whilst this relationship is diminished with advanced age. In contrast, we found no correlation between physical fitness and sleep characteristics in healthy young or older participants, which may explain the lack of improvement in sleep characteristics in older participants with 12-month exercise training. Exercise training may be more successful in subjects with existing sleep disturbances to improve sleep characteristics rather than in healthy older subjects.

Hormone and metabolite changes associated with extended breeding fasts in male northern elephant seals (Mirounga angustirostris)

We measured metabolic hormones and several key metabolites in breeding adult male northern elephant seals to examine the regulation of fuel metabolism during extended natural fasts of over 3months associated with high levels of energy expenditure. Males were sampled twice, early and late in the fast, losing an average of 23% of body mass and 47% of adipose stores between measurements. Males exhibited metabolic homeostasis over the breeding fast with no changes in glucose, non-esterified fatty acids, or blood urea nitrogen. Ketoacids increased over the fast but were very low when compared to other fasting species. Changes within individuals in total triiodothyronine (tT3) were positively related to daily energy expenditure (DEE) and protein catabolism. Differences in levels of thyroid hormones relative to that observed in weaned pups and females suggest a greater deiodination of T4 to support the high DEE of breeding males. Relative levels of leptin and ghrelin were consistent with the suppression of appetite but a significant reduction in growth hormone across the fast was contrary to expectation in fasting mammals. The lack of the increase in cortisol during fasting found in conspecific weaned pups and lactating females may contribute to the ability of breeding males to spare protein despite high levels of energy expenditure. Together these findings reveal significant differences with conspecifics under varying nutrient demands, suggesting metabolic adaptation to extended high energy fasts.

Energy expenditure during egg laying is equal for early and late breeding free-living female great tits

In many bird populations, variation in the timing of reproduction exists but it is not obvious how this variation is maintained as timing has substantial fitness consequences. Daily energy expenditure (DEE) during the egg laying period increases with decreasing temperatures and thus perhaps only females that can produce eggs at low energetic cost will lay early in the season, at low temperatures. We tested whether late laying females have a higher daily energy expenditure during egg laying than early laying females in 43 great tits (Parus major), by comparing on the same day the DEE of early females late in their laying sequence with DEE of late females early in their egg laying sequence. We also validated the assumption that there are no within female differences in DEE within the egg laying sequence. We found a negative effect of temperature and a positive effect of female body mass on DEE but no evidence for differences in DEE between early and late laying females. However, costs incurred during egg laying may have carry-over effects later in the breeding cycle and if such carry-over effects differ for early and late laying females this could contribute to the maintenance of phenotypic variation in laying dates.

Evolutionary models of metabolism, behaviour and personality.

I explore the relationship between metabolism and personality by establishing how selection acts on metabolic rate and risk-taking in the context of a trade-off between energy and predation. Using a simple time budget model, I show that a high resting metabolic rate is not necessarily associated with a high daily energy expenditure. The metabolic rate that minimizes the time spent foraging does not maximize the net gain rate while foraging, and it is not always advantageous for animals to have a higher metabolic rate when food availability is high. A model based on minimizing the ratio of mortality rate to net gain rate is used to determine how a willingness to take risks should be correlated with metabolic rate. My results establish that it is not always advantageous for animals to take greater risks when metabolic rate is high. When foraging intensity and metabolic rate coevolve, I show that in a particular case different combinations of foraging intensity and metabolic rate can have equal fitness.

Fructose, Exercise, and Health

The large daily energy intake common among athletes can be associated with a large daily intake of fructose, a simple sugar that has been linked to metabolic disorders. Fructose commonly is found in foods and beverages as a natural component (e.g., in fruits) or as an added ingredient (as sucrose or high fructose corn syrup [HFCS]). A growing body of research suggests that excessive intake of fructose (e.g., >50 g.d(-1)) may be linked to development of the metabolic syndrome (obesity, dyslipidemia, hypertension, insulin resistance, proinflammatory state, prothrombosis). The rapid metabolism of fructose in the liver and resultant drop in hepatic adenosine triphosphate (ATP) levels have been linked with mitochondrial and endothelial dysfunction, alterations that could predispose to obesity, diabetes, and hypertension. However, for athletes, a positive aspect of fructose metabolism is that, in combination with other simple sugars, fructose stimulates rapid fluid and solute absorption in the small intestine and helps increase exogenous carbohydrate oxidation during exercise, an important response for improving exercise performance. Although additional research is required to clarify the possible health-related implications of long-term intake of large amounts of dietary fructose among athletes, regular exercise training and consequent high daily energy expenditure may protect athletes from the negative metabolic responses associated with chronically high dietary fructose intake.

Effects of dietary protein intake on lactation performance of the laboratory mouse, &lt;i&gt;Mus musculus&lt;/i&gt;

Laboratory mice (strain MF1) were used to investigate the effects of dietary protein content on lactation performance to test the heat dissipation limit hypothesis. The specific dynamic action (SDA) for high protein (HP) and high carbohydrate (HC) diets was measured using open-flow respirometry at 9.4% and 6.1%, respectively. The same two diets were fed ad libitum to mice during lactation. Mice fed on HP and HC diets at 21 ºC reached a plateau in their daily food intake at 12.3±0.2 g day-1 and 16.6±0.2 g day-1, respectively between days 12-17 of lactation. HP-fed mice had a significantly higher daily energy expenditure (DEE) measured by doubly labelled water and higher water turnover than HC-fed mice but the energy they exported as milk was significantly lower than that of HC-fed mice and therefore resulted in poor growth rate of their offspring. The urea production of HP-fed mice from their daily protein intake of 7.1 g was estimated at 1994 mg which required 10.2 mls of water per day to be cleared. The mice increased their urine production by 14.4 mls probably to eliminate this urea. High protein diet had negative effects on lactation, indicating the growth of pups in previous studies was not protein limited. The negative effects of the HP diet were due to the high DEE that greatly reduced the energy available for milk production, rather than a toxicity effect of the urea production. The different DEE of the two diets suggests that other factors were involved in the delivery of energy to the offspring.KEY WORDS: Laboratory mouse, dietary protein, specific dynamic action, and daily energy expenditure

Effects of structural and functional habitat gaps on breeding woodland birds: working harder for less

The effects of habitat gaps on breeding success and parental daily energy expenditure (DEE) were investigated in great tits (Parus major) and blue tits (Cyanistes caeruleus) in urban parkland (Cardiff, UK) compared with birds in deciduous woodland (eastern England, UK). Tree canopy height, the percentage of gap in the canopy and the percentage of oak (in the wood only) within a 30 m radius of nest boxes were obtained from airborne remote-sensed data. Breeding success was monitored and parental DEE (great tits: both habitats; blue tits: park only) was measured using doubly labelled water in birds feeding young. In the park, mean (±SD) tree height (7.5 ± 4.7 m) was less than in the wood (10.6 ± 4.5 m), but the incidence of gaps (32.7 ± 22.6%) was greater (9.2 ± 14.7%). Great tits and blue tits both reared fewer young in the park and chick body mass was also reduced in park-reared great tits. Park great tits had a higher DEE (86.3 ± 12.3 kJ day -1 ) than those in the wood (78.0 ± 11.7 kJ day -1 ) and, because of smaller brood sizes, worked about 64% harder for each chick reared. Tits in the park with more than about 35% gap around their boxes had higher DEEs than the average for the habitat. In the wood, great tits with less oak around their boxes worked harder than average. Thus structural gaps, and functional gaps generated by variation in the quality of foraging habitat, increased the costs of rearing young.

Sex- and concentration-dependent effects of predator feces on seasonal regulation of body mass in the bank vole Clethrionomys glareolus

Increased perception of predation risk can cause changes in activity, feeding and reproductive behavior in a wide range of taxa. Many small mammals in the temperate zone exhibit fluctuations in body mass in response to changing photoperiod. Bank voles lose body mass in winter which they regain when photoperiod increases in the spring. To determine if predation risk affects seasonal changes in body mass (BM), bank voles were exposed to two concentrations (low: LC and high: HC) of weasel feces. Food intake (FI) and daily energy expenditure (DEE) were measured to establish if differences in body mass were due to adjustment in energy intake or expenditure. Fecal corticosterone (CORT) was measured to assess whether the voles had detected and responded to predator feces as a physiological stressor. Voles of both sexes had higher levels of fecal CORT in the groups exposed to weasel feces compared to controls. Voles responded to the predator feces in a sex- and concentration-dependent manner. Males responded to LC feces by gaining less mass following the change in photoperiod. This was mediated by reduced FI and higher DEE. Female voles also gained less BM in response to HC feces, but increased both FI and DEE. We hypothesize that males may gain a short-term advantage by lowering BM in response to predation risk, which may be regained without affecting reproductive success. The consequences of mass loss in females may be more significant as this may delay the onset of breeding or reduce the size or number of young, thereby negatively affecting breeding success.

Seasonal sex–specific energy expenditure in breeding and non‐breeding Palestine sunbirds Nectarinia osea

The timing of the chick‐rearing phase is known to have a profound effect on the reproductive success of birds. However, little is known about the energetic costs faced by the parents during different periods of the breeding season. These costs may have vital consequences for both their survival and future reproduction. In most studies, daily energy expenditure (DEE) of breeding and non‐breeding birds has been compared, without controlling for the effect of season. In the present study, we examined the energy demands of breeding compared to non‐breeding Palestine sunbirds Nectarinia osea and whether there were sex‐specific differences in DEE within and between different seasons. We predicted that DEE would be elevated when birds rear chicks, especially at cooler ambient temperatures. Time‐energy budgets were constructed for pairs of sunbirds, rearing chicks, or not breeding, in spring and summer. There were significant seasonal differences in estimates of DEE in non‐breeders that were 21% higher in spring than in summer. We attributed these to increases in non‐flight metabolic rate rather than changes in time spent on different activities. Our estimates of DEE for the birds that were rearing chicks were higher than non‐breeding adults. In females the increase in DEE when breeding, compared to when not breeding, was similar in both spring and summer, while males increased their DEE much less when breeding in spring. The differences in estimated DEE, however, were not significant between male and female birds in any season. Between seasons, female breeders had 17.1% higher DEE in spring than in summer, while male breeders showed no difference in DEE when rearing chicks in different seasons. Accordingly, our initial prediction was supported, as DEE in chick‐rearing adults was higher than in non‐breeding adults. In addition, although temperatures are lower in spring, breeding in the spring is only more costly than breeding in summer for females. Apparently, males are more flexible in reallocating their time and energy spent on different activities.

INDIVIDUALLY VARIABLE ENERGY MANAGEMENT STRATEGIES IN RELATION TO ENERGETIC COSTS OF EGG PRODUCTION

Marked interindividual variation in metabolic rate suggests considerable complexity in energy management strategies, but attempts to further our understanding of the relationship between resting metabolic rate (RMR), daily energy expenditure (DEE), and reproductive effort have been hampered by the complexity of studying this system in the field. Here, we describe energy management strategies in a captive-breeding system, using Zebra Finches (Taeniopygia guttata), to demonstrate the high level of complexity and interindividual variability in energy expenditure, food intake, locomotor activity, and reproductive effort. In particular, we investigated whether the increase in RMR associated with egg production is additive, resulting in higher DEE and a need for elevated food intake, or whether this cost is compensated by reduced expenditure in nonreproductive components of the energy budget. We found high levels of intra-individual variation in energy expenditure associated with egg production in female Zebra Finches, e.g., comparing nonbreeding stage with the one-egg stage, change in RMR varied from 4.0% and 41.3%, and change in DEE varied from -33.3% to +46.4%. This variation was systematically related to aspects of locomotor activity and reproductive effort. Females with the largest increase in RMR during egg production decreased locomotor activity the most but still had increased DEE at the one-egg stage, and females with high DEE at the one-egg stage produced larger clutches. Our study suggests that females minimize increases in DEE during egg production through behavioral energy reallocation (reduced locomotor activity) but that individuals differ in their use of this strategy, which, in turn, is related to the absolute level of reproductive investment. This suggests a very complex, individually variable system of energy management to meet the demands of egg production.

Estimated daily energy expenditure and blood lipids in adolescents: the Québec family study

Purpose To examine the association between estimated daily energy expenditure and blood lipids in a sample of adolescents. Methods The sample consisted of 415 males and 356 females aged 10–19 years, mainly French Canadian, recruited from the greater Quebec City area through the media as part of Phase I of the Quebec Family Study. Estimates of daily energy expenditure (DEE) were obtained with a 3-day physical activity record. Blood lipids were measured by standard procedures. The sample was stratified into three activity groups (least active, less than 25th percentile of DEE; moderately active, 25–74th percentile of DEE; and most active, 75th percentile or greater of DEE), and also by clinical cutpoints for blood lipids. Analysis of covariance, controlling for age and fatness, was conducted to compare blood lipids within gender across activity groups. Logistic regression analysis, controlling for age and fatness, was used to estimate the relative risk of being classified with an undesirable level of a blood lipid parameter on the basis of the DEE. Results Total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels were not significantly different across activity groups in males or females. High-density lipoprotein cholesterol (HDL-C) was significantly different across activity groups in males ( p < .05) and females ( p < .05), but the pattern of variation was different between genders. In males, the TC/HDL-C and LDL-C/HDL-C ratios decreased between the moderately active and most active groups ( p < .05). Significant differences remained when subcutaneous fatness was considered as a covariate. The results from logistic regression analysis indicated that the odds ratios for low HDL-C levels was significant only in low DEE girls (odds ratio 2.83) compared with high DEE girls. Conclusions The results suggest that increased energy expenditure and physical activity are associated with higher levels of HDL-C in adolescents of both sexes.

High daily energy expenditure of incubating shorebirds on High Arctic tundra: a circumpolar study

Summary Given the allometric scaling of thermoregulatory capacity in birds, and the cold and exposed Arctic environment, it was predicted that Arctic‐breeding shorebirds should incur high costs during incubation. Using doubly labelled water (DLW), daily energy expenditure (DEE) during incubation was measured in eight shorebird species weighing between 29 and 142 g at various sites in the Eurasian and Canadian High Arctic. The results are compared with a compilation of similar data for birds at lower latitudes. There was a significant positive correlation between species average DEE and body mass (DEE (kJ day−1) = 28·12 BM (g)0·524, r2 = 0·90). The slopes of the allometric regression lines for DEE on body mass of tundra‐breeding birds and lower latitude species (a sample mostly of passerines but including several shorebirds) are similar (0·548 vs 0·545). DEE is about 50% higher in birds on the tundra than in temperate breeding areas. Data for radiomarked Red Knots for which the time budgets during DLW measurements were known, indicated that foraging away from the nest on open tundra is almost twice as costly as incubating a four‐egg clutch. During the incubation phase in the High Arctic, tundra‐breeding shorebirds appear to incur among the highest DEE levels of any time of the year. The rates of energy expenditure measured here are among the highest reported in the literature so far, reaching inferred ceilings of sustainable energy turnover rates.

Daily Energy Expenditure of Ovenbirds (Seiurus aurocapillus) Feeding Nestlings

AbstractThe doubly labeled water method was used to measure daily energy expenditure of adult Ovenbirds (Seiurus aurocapillus) feeding nestlings in large and small forests in northern New England. Carbon dioxide production for all birds averaged 7.67 ± 1.29 mL g−1 hr−1 (n = 27), equivalent to 90.1 ± 15.0 kJ day−1. Carbon dioxide production did not differ between males and females within the same pair measured over the same period. Ratio of daily energy expenditure to basal metabolic rate (BMR) for Ovenbirds (3.4) was closer to the mean value derived for aerial foragers (3.8) than that for ground foragers (2.3) in a sample of passerines feeding nestlings. High daily energy expenditure for Ovenbirds may be related to their relatively brief breeding season in northern climates and their use of cool, closed-canopy forests. Although daily energy expenditure for Ovenbirds was high when compared to other ground-foraging passerines, most individuals were not working near the hypothetical maximum of 4× BMR (Drent and Daan 1980). Daily energy expenditure for Ovenbirds feeding young was greater in large forests than small forests, although the difference was not statistically significant. We speculate that time used for foraging (and hence energy expenditure) may be lower in small forests as a result of increased prey density, or alternatively, greater risk of nest predation in forest fragments leads to greater vigilance at the nest site and less time available for foraging. Further studies of avian energetics in large and small forests, including detailed time–activity budgets, may reveal hidden costs of forest fragmentation.

Daily Energy Expenditure of Ovenbirds (Seiurus aurocapillus) Feeding Nestlings

The doubly labeled water method was used to measure daily energy expenditure of adult Ovenbirds (Seiurus aurocapillus) feeding nestlings in large and small forests in northern New England. Carbon dioxide production for all birds averaged 7.67 ± 1.29 mL g−1 hr−1 (n = 27), equivalent to 90.1 ± 15.0 kJ day−1. Carbon dioxide production did not differ between males and females within the same pair measured over the same period. Ratio of daily energy expenditure to basal metabolic rate (BMR) for Ovenbirds (3.4) was closer to the mean value derived for aerial foragers (3.8) than that for ground foragers (2.3) in a sample of passerines feeding nestlings. High daily energy expenditure for Ovenbirds may be related to their relatively brief breeding season in northern climates and their use of cool, closed-canopy forests. Although daily energy expenditure for Ovenbirds was high when compared to other ground-foraging passerines, most individuals were not working near the hypothetical maximum of 4× BMR (Drent and Daan 1980). Daily energy expenditure for Ovenbirds feeding young was greater in large forests than small forests, although the difference was not statistically significant. We speculate that time used for foraging (and hence energy expenditure) may be lower in small forests as a result of increased prey density, or alternatively, greater risk of nest predation in forest fragments leads to greater vigilance at the nest site and less time available for foraging. Further studies of avian energetics in large and small forests, including detailed time–activity budgets, may reveal hidden costs of forest fragmentation.

Wintering Tufted Ducks Aythya fuligula Diving for Zebra Mussels Dreissena polymorpha Balance Feeding Costs within Narrow Margins of Their Energy Budget

Diving ducks face the strongly cooling properties of aquatic environments. In experiments with Tufted Ducks Aythya fuligula feeding on zebra mussels Dreissena polymorpha in outdoor cages, we measured changes in food consumption and diving behaviour in relation to water temperature (3-22 degrees C). Water efflux and daily energy expenditure (DEE) were measured using doubly-labelled water. Tufted Ducks swallow mussels whole and crush the shells in the gizzard. Due to the low flesh content of mussels, daily mussel consumption was extremely high in winter (up to 3 times the duck body mass of 600 g). Water efflux was 6.5 to 13 limes higher than allometrically predicted, with a maximum of 1.1 1 d(-1). Because of high water turnover rates, DEE estimates from doubly-labelled water measurements were variable, but on average agreed with DEE estimates obtained from food consumption and time-energy budgets (ca. 5% higher values). DEE increased with lower temperatures from 2.5 (summer, 20 degrees C) to more than 4 times the basal metabolic rate (winter, 3 degrees C). Costs of thermoregulation and heating up ingested mussels (as estimated from the theoretical caloric heat) primarily explained the high DEE in winter. At lower temperatures, dive duration was shorter and less time was spent selecting small mussels at the bottom, while more larger mussels were brought up and were ingested at the water surface. Thereby, the energy costs of crushing shells probably increased in favour of reducing diving costs. The narrow margins of the energy budget, wherein feeding costs must be balanced, imply that food availability and water temperature are important attributes to winter distributions of diving ducks.

Field metabolic rate and cost of activity in two tenebrionid beetles from the Mojave Desert of North America

Ectotherms which survive for more than one year in the desert must be able to cope with a variety of seasonal changes, such as temperature regimes and food availability. As temperature and food availability vary, the organism must adjust its activity and energetic expenditure in response to these external influences. Two sympatric tenebrionid beetles ( Eleodes armata and Cryptoglossa verrucosa ) of the Mojave Desert of North America were studied in both laboratory and field to determine how energy requirements varied over a year. By combining laboratory and field measurements of metabolic rate, the cost of activity was determined for these two species of beetles. In all seasons, E. armata had higher daily energy expenditure (DEE) and higher daily maintenance (resting) energy expenditure (DREE) than C. verrucosa, although the daily cost of activity (difference between DEE and DREE) was often similar. Increasing temperature and body mass increased laboratory oxygen consumption rates and field metabolic rates for both species. Metabolic rate of C. verrucosa did appear to be more sensitive to temperature than that of E. armata, as indicated by a multiple regression. This data suggests that E. armata can exploit a wider range of temperature regimes than C. verrucosa. The metabolic responses may reflect a phylogenetic or historical difference, as E. armata is thought to have evolved in montane habitats with a 'recent' invasion of deserts and C. verrucosa is considered to be endemic to deserts.

Individual and population energetics of a lizard on a Mediterranean islet.

Population density in the lacertid lizardPodarcis lilfordi on the Mediterranean islet of Nitge, Menorca, Balearic Islands, was found to be 12 190 ind · ha-1 (SE, ±2135), exceeding densities reported for other island or mainland lizard populations. Field metabolic rates inP. lilfordi were measured by the doubly labeled water method, allowing estimation of a population metabolizable energy demand of 13.86 MJ · ha-1 · day-1-only 9.8% of that for a theoretical mammal population of the same body mass and density. Energy demand was considerably higher than that estimated for other lizard populations, primarily due to high population density but also because of high individual daily energy expenditure (1255 KJ · day-1; body mass=5.13 g). Field metabolic rates were partitioned into maintenance and activity components by respirometry of captive animals at field body temperatures. Activity metabolism formed the main component (77.4%) of total respiratory metabolism resulting from a combination of long daily activity periods (ca. 12 h), and greatly elevated metabolism during activity (5.7 times greater than resting levels). It is hypothesized that low food availability per individual constrains the time-energy budget of this species, obligating long periods of intense foraging.

Energy Expenditure in Adult Least Auklets and Diving Petrels during the Chick-Rearing Period

Energy expenditure rates of three high-latitude seabirds (least auklet [Aethia pusilla], common diving petrel [Pelecanoides urinatrix], and South Georgia diving petrel [P. georgicus]) were measured during the chick-rearing period to test the hypothesis that power requirements for reproduction in pursuit divers are high relative to other seabirds. Oxygen consumption of resting adults was measured volumetrically using a temperature-controlled, closed system. Carbon dioxide production in free-ranging adults during the chick-rearing period was measured using the doubly labeled water (DLW) method. Standard metabolic rates (SMR) were 1.5 to 1.9 times predictions of allometric equations relating SMR to body mass in nonpasserine birds. Mass-specific CO₂ production and fractional water-turnover rates in free-ranging adults were similar in the three study species. The daily energy expenditure (DEE)/SMR ratio ranged from 3.1 to 4.2. Among values of DEE for breeding birds measured by the DLW method, those obtained in this study were relatively high. Energy expenditure is apparently elevated in pursuit divers by high power requirements for flight and foraging, as surface-feeding seabirds had lower relative energy expenditures. The low gross foraging efficiency and high DEEs of the auklet and diving petrels suggest that the high energetic cost of foraging and food delivery to the nest constrains brood size.