Estimates Of Field Metabolic Rate Research Articles

Incorporating otolith-isotope inferred field metabolic rate into conservation strategies.

Fluctuating ocean conditions are rearranging whole networks of marine communities-from individual-level physiological thresholds to ecosystem function. Physiological studies support predictions from individual-level responses (biochemical, cellular, tissue, respiratory potential) based on laboratory experiments. The otolith-isotope method of recovering field metabolic rate has recently filled a gap for the bony fishes, linking otolith stable isotope composition to in situ oxygen consumption and experienced temperature estimates. Here, we review the otolith-isotope method focusing on the biochemical and physiological processes that yield estimates of field metabolic rate. We identify a multidisciplinary pathway in the application of this method, providing concrete research goals (field, modeling) aimed at linking individual-level physiological data to higher levels of biological organization. We hope that this review will provide researchers with a transdisciplinary 'roadmap', guiding the use of the otolith-isotope method to bridge the gap between individual-level physiology, observational field studies, and modeling efforts, while ensuring that in situ data is central in marine policy-making aimed at mitigating climatic and anthropogenic threats.

Direct measurement of cruising and burst swimming speeds of the shortfin mako shark (Isurus oxyrinchus) with estimates of field metabolic rate.

The shortfin mako shark is a large-bodied pursuit predator thought to be capable of the highest swimming speeds of any elasmobranch and potentially one of the highest energetic demands of any marine fish. Nonetheless, few direct speed measurements have been reported for this species. Here, animal-borne bio-loggers attached to two mako sharks were used to provide direct measurements of swimming speeds, kinematics and thermal physiology. Mean sustained (cruising) speed was 0.90 m s-1 (±0.07 s.d.) with a mean tail-beat frequency (TBF) of 0.51 Hz (±0.16 s.d.). The maximum burst speed recorded was 5.02 m s-1 (TBFmax = 3.65 Hz) from a 2 m long female. Burst swimming was sustained for 14 s (mean speed = 2.38 m s-1 ), leading to a 0.24°C increase in white muscle temperature in the 12.5 min after the burst. Routine field metabolic rate was estimated at 185.2 mg O2 kg-1 h-1 (at 18°C ambient temperature). Gliding behaviour (zero TBF) was more frequently observed after periods of high activity, especially after capture when internal (white muscle) temperature approached 21°C (ambient temperature: 18.3°C), indicating gliding probably functions as an energy recovery mechanism and limits further metabolic heat production. The results show shortfin mako sharks generally cruise at speeds similar to other endothermic fish - but faster than ectothermic sharks - with the maximum recorded burst speed being among the highest so far directly measured among sharks, tunas and billfishes. This newly recorded high-oxygen-demand performance of mako sharks suggests it may be particularly vulnerable to habitat loss due to climate-driven ocean deoxygenation.

Individual variation in field metabolic rates of wild living fish have phenotypic and ontogenetic underpinnings: insights from stable isotope compositions of otoliths

IntroductionIndividual metabolism has been identified as a key variable for predicting responses of individuals and populations to climate change, particularly for aquatic ectotherms such as fishes. Predictions of organism standard metabolic rate (SMR), and the thermal sensitivity of metabolic rate are typically based on allometric scaling rules and respirometry-based measures of respiratory potential under laboratory conditions. The relevance of laboratory-based measurement and theoretical allometric rules to predict performance of free-ranging animals in complex natural settings has been questioned, but determining time averaged metabolic rate in wild aquatic animals is challenging.MethodsHere we draw on stable isotope compositions of aragonite in fish otoliths to estimate time averaged experienced temperature and expressed field metabolic rate (FMR) simultaneously and retrospectively at an individual level. We apply the otolith FMR proxy to a population of European plaice (Pleuronectes platessa) from the North Sea during a period of rapid warming between the 1980s to the mid-2000s, sampling otolith tissue grown in both juvenile and adult stages.ResultsAmong-individual variations in realized mass-specific FMR were large and independent of temperature and scaled positively with body size in adult life stages, contradicting simplistic assumptions that FMR follows scaling relationships inferred for standard metabolic rates (SMR). In the same individuals, FMR in the first summer of life co-varied positively with temperature.DiscussionWe find strong evidence for the presence of consistent metabolic phenotypes within the sampled population, as FMR in the first year of life was the strongest single predictor for among individual variation in FMR at the point of sampling. Nonetheless, best fitting models explained only 20% of the observed variation, pointing to large among-individual variation in FMR that is unexplained by body mass, temperature or metabolic phenotype. Stable isotope-derived estimates of field metabolic rate have great potential to expand our understanding of ecophysiology in general and especially mechanisms underpinning the relationships between animal performance and changing environmental and ecological conditions.

Sluggish metabolism keeps Greenland sharks going on meagre meals

Apparently, Greenland shark is an acquired taste. The meat of these leviathans, tainted with urea and toxic trimethylamine N-oxide, requires fermentation and drying before it is safe to consume. But the long-lived giants of the deep are coming under increasing threat as they compete with humans for their own preferred delicacy, Greenland halibut. And their Arctic home is one of the fastest warming regions on the planet, putting these monsters in even more danger. ‘If we understand their energy requirements in the wild, we can estimate how much food they need to eat and hypothesise about their survival strategies’, says Eric Ste-Marie from The University of Windsor, Canada, adding that it is increasingly important to predict how they will be impacted by these threats. Together with Nigel Hussey (University of Windsor), Yuuki Watanabe (National Institute of Polar Research, Japan), Marianne Marcoux (Fisheries and Ocean Canada), in collaboration with Jayson Semmens (University of Tasmania, Australia), Ste-Marie headed north to Nunavut to go shark fishing.Working with local hunters and trappers, the team set long fishing lines baited with shark treats in the Scott Inlet, Nunavut, and further north in Tremblay Sound, capturing 30 sharks over a 5 year period before carefully hauling the animals to the surface, measuring their length and attaching a temperature and motion sensor behind the head to monitor their activity. ‘Seeing a Greenland shark up close is a unique experience. Their movements are slow but powerful, their eyes are typically cloudy and their skin feels like sandpaper’, says Ste-Marie, adding that the animals were usually calm once secured alongside a boat. The team then retrieved each tag when it detached up to 48 h later. ‘Arctic field work poses unique challenges: wind, water and ice conditions often change quickly, making tag recovery difficult, especially on days when we had multiple tags to recover or when sharks swam tens of kilometres away’, says Ste-Marie.Having previously learned from Watanabe how to extract information from the movements recorded by motion sensors, Ste-Marie painstakingly analysed the lethargic sharks’ manoeuvres and calculated how fast they beat their tails. In addition, he estimated each animal's mass, based on their length, and calculated their metabolic rate as they propelled themselves through the depths. After months of patient calculation, Ste-Marie determined that the shark's metabolic rate is ∼21.7 mg O2 h−1 kg–0.84, compared with 187–506 mg O2 kg−0.86 for bull sharks, although the metabolic rate that he determined for a smaller group of sharks wearing an activity monitor for a whole year was slightly higher (∼25.5 mg O2 h−1 kg–0.84).But how much food does that translate into? Converting the metabolic rate into energy use and then into the amount of fish a shark would have to consume to provide that energy, Ste-Marie calculated that an average 224 kg shark must consume 164–193 g of fish each day. So, a shark could keep going for 5–6 days on a 1 kg Greenland halibut meal, while a 15 kg narwhal snack would support a shark for up to 175 days and 15 kg of ringed seal could sustain an animal for up to 250 days – over 8 months – before it needed to dine again.‘Our estimates of field metabolic rate were very low across the sharks in our study. They likely do not require much energy and food to fuel their daily lives, which may allow them to survive extended periods without feeding’, says Ste-Marie, who is keen to find out how often these massive fish depend on scavenging or pursuing tasty treats to satisfy their meagre appetites.

Why Baja? A bioenergetic model for comparing metabolic rates and thermoregulatory costs of gray whale calves (Eschrichtius robustus)

AbstractA bioenergetic model is developed from empirically derived equations of morphometric, ventilatory and thermoregulatory variables to compare estimated field metabolic rates (FMR) of gray whale calves to estimates of unregulated body heat losses and consequent required thermogenesis at birth, natal lagoon departure, and weaning. Estimates of FMR are based on rates of oxygen consumption. Body surface and ventilatory heat fluxes are evaluated separately, then combined to estimate minimum total heat losses from birth to weaning at three ambient water temperature regimes typical of winter natal lagoons and Oregon coastal waters and arctic conditions during summer.Modeled heat losses of neonates in winter lagoons are half their estimated mean FMR. Neonates in good body condition appear to be capable of tolerating heat losses experienced in 10°C water without additional thermogenic activities above their estimated resting metabolic rates. This study provides new evidence that no thermoregulatory advantage accrues to neonates or to their mothers by being born in warm winter natal lagoons or by remaining there several weeks longer than other gray whales. Consequently, avoidance or reduced risk of killer whale predation seems a more likely candidate than reduced heat loss as the principal fitness benefit of low‐latitude winter migrations.

High field metabolic rates of wild harbour porpoises.

Reliable estimates of field metabolic rates (FMRs) in wild animals are essential for quantifying their ecological roles, as well as for evaluating fitness consequences of anthropogenic disturbances. Yet, standard methods for measuring FMR are difficult to use on free-ranging cetaceans whose FMR may deviate substantially from scaling predictions using terrestrial mammals. Harbour porpoises (Phocoena phocoena) are among the smallest marine mammals, and yet they live in cold, high-latitude waters where their high surface-to-volume ratio suggests high FMRs to stay warm. However, published FMR estimates of harbour porpoises are contradictory, with some studies claiming high FMRs and others concluding that the energetic requirements of porpoises resemble those of similar-sized terrestrial mammals. Here, we address this controversy using data from a combination of captive and wild porpoises to estimate the FMR of wild porpoises. We show that FMRs of harbour porpoises are up to two times greater than for similar-sized terrestrial mammals, supporting the hypothesis that small, carnivorous marine mammals in cold water have elevated FMRs. Despite the potential cost of thermoregulation in colder water, harbour porpoise FMRs are stable over seasonally changing water temperatures. Varying heat loss seems to be managed via cyclical fluctuations in energy intake, which serve to build up a blubber layer that largely offsets the extra costs of thermoregulation during winter. Such high FMRs are consistent with the recently reported high feeding rates of wild porpoises and highlight concerns about the potential impact of human activities on individual fitness and population dynamics.

Accelerometers can measure total and activity‐specific energy expenditures in free‐ranging marine mammals only if linked to time‐activity budgets

Summary Energy expenditure is an important component of foraging ecology, but is extremely difficult to estimate in free‐ranging animals and depends on how animals partition their time between different activities during foraging. Acceleration data have emerged as a new way to determine energy expenditure at a fine scale but this needs to be tested and validated in wild animals. This study investigated whether vectorial dynamic body acceleration (VeDBA) could accurately predict the energy expended by marine predators during a full foraging trip. We also aimed to determine whether the accuracy of predictions of energy expenditure derived from acceleration increased when partitioned by different types of at‐sea activities (i.e. diving, transiting, resting and surface activities). To do so, we equipped 20 lactating northern (Callorhinus ursinus) and 20 lactating Antarctic fur seals (Arctocephalus gazella) with GPS, time‐depth recorders and tri‐axial accelerometers and obtained estimates of field metabolic rates using the doubly labelled water (DLW) method. VeDBA was derived from tri‐axial acceleration, and at‐sea activities (diving, transiting, resting and surface activities) were determined using dive depth, tri‐axial acceleration and travelling speed. We found that VeDBA did not accurately predict the total energy expended by fur seals during their full foraging trips (R2 = 0·36). However, the accuracy of VeDBA as a predictor of total energy expenditure increased significantly when foraging trips were partitioned by activity and when activity‐specific VeDBA was paired with time‐activity budgets (R2 = 0·70). Activity‐specific VeDBA also accurately predicted the energy expenditures of each activity independent of each other (R2 > 0·85). Our study confirms that acceleration is a promising way to estimate energy expenditures of free‐ranging marine mammals at a fine scale never attained before. However, it shows that it needs to be based on the time‐activity budgets that make up foraging trips rather than being derived as a single measure of VeDBA applied to entire foraging trips. Our activity‐based method provides a cost‐effective means to accurately calculate energy expenditures of fur seals using acceleration and time‐activity budgets, that can be transfered to studies on other species.

Quantifying the predation on sardine and hake by cetaceans in the Atlantic waters of the Iberian peninsula

Construction of ecosystem models requires detailed information on trophic interactions which may not be readily available, especially for top predators such as cetaceans. Such information can also be useful to estimate natural mortality (M) for fish stock assessments and to evaluate the potential for competition between cetaceans and fisheries. In the present paper we provide estimates and confidence limits, taking into account sampling error, for consumption of fish by the four most common cetaceans along the Atlantic coast of the Iberian Peninsula, while highlighting the uncertainties and biases inherent in the information presently available on energy requirements, diet and population size. We estimated that common dolphins (Delphinus delphis) consume around 6800 (95% CI, 4871–9476) tons of sardine (Sardina pilchardus), 8800 (6195–12,647) tons of gadids, 1100 (721–1662) tons of hake (Merluccius merluccius) and 1900 (1222–2752) tons of scads (Trachurus sp.) annually. For striped dolphins (Stenella coeruleoalba), prey consumed were 900 (196–2661) tons of sardine, 6200 (3448–11,129) tons of gadids, 200 (11–504) tons of hake and 1600 (0–5318) tons of scads. Estimated amounts taken by harbour porpoises (Phocoena phocoena) and bottlenose dolphins (Tursiops truncatus) are much lower, reflecting their low abundance in the area. Cetacean predation on sardine represents 2–8% of the current M value, indicating that cetaceans probably have little influence on sardine population dynamics. For the southern hake stock, estimated average removal by cetaceans often exceeds M. While this may indicate that both M and the consumption estimates for hake require revision it also suggests that cetaceans could have a more significant impact on hake populations. Different approaches to estimation of energy requirements of cetaceans can result in figures that differ by at least a factor of 2. The lack of good estimates of field metabolic rate for most species probably represents the most serious barrier to reliably quantifying the role of cetaceans in the ecosystem.

Estimating field metabolic rates of pinnipeds: doubly labelled water gets the seal of approval

Summary 1. Measures of the field metabolic rate of marine mammals are extremely difficult to make but they are essential for assessing the impacts of marine mammals on prey populations, and for assessing dive performance in relation to aerobic limits. 2. The doubly labelled water (DLW) method is an isotope-based technique for the estimation of the CO 2 production, and hence energy expenditure, of free-living animals. Estimates of field metabolic rate (FMR) from DLW in pinnipeds to date are extremely high and at the upper range for most mammals. DLW has previously been validated in pinnipeds but logistical difficulties meant for these validations were less than ideal, and it has been hypothesised that DLW may overestimate FMR in these animals. 3. To test this hypothesis, we used DLW and simultaneous open-flow respirometry to determine the daily energy expenditures (DEE) of wild grey seals ( Halichoerus grypus ) held temporarily in a captive facility, during 4‐5 days of simulated foraging at sea. Comparing DEE from DLW and respirometry, we found that DLW predicted DEE accurately (average difference between the two estimates was 0·7% SD = 17% n = 31), but as with validations of other species there was a large range of individual errors (from ‐39% to +44%). 4. The results dispel the doubts surrounding the use of DLW as a field method for estimating energy expenditure in grey seals, and by implication other pinnipeds, and simultaneously open a series of questions about their ability to maintain surprisingly high metabolic rates for protracted periods. 5. We make a number of recommendations for future studies of pinniped FMR using DLW. We suggest use of the Speakman two-pool calculation will be most appropriate. Studies should aim for enrichment levels as high as economically feasible but to at least 150 p.p.m. above background for the O 2 isotope. Measurement periods should be extended between one and two half-lives (5‐10 days for a typical foraging seal). We also encourage the calculation and presentation of estimates of precision in estimates of FMR.

Behavioral Inference of Diving Metabolic Rate in Free‐Ranging Leatherback Turtles

Good estimates of metabolic rate in free-ranging animals are essential for understanding behavior, distribution, and abundance. For the critically endangered leatherback turtle (Dermochelys coriacea), one of the world's largest reptiles, there has been a long-standing debate over whether this species demonstrates any metabolic endothermy. In short, do leatherbacks have a purely ectothermic reptilian metabolic rate or one that is elevated as a result of regional endothermy? Recent measurements have provided the first estimates of field metabolic rate (FMR) in leatherback turtles using doubly labeled water; however, the technique is prohibitively expensive and logistically difficult and produces estimates that are highly variable across individuals in this species. We therefore examined dive duration and depth data collected for nine free-swimming leatherback turtles over long periods (up to 431 d) to infer aerobic dive limits (ADLs) based on the asymptotic increase in maximum dive duration with depth. From this index of ADL and the known mass-specific oxygen storage capacity (To(2)) of leatherbacks, we inferred diving metabolic rate (DMR) as To2/ADL. We predicted that if leatherbacks conform to the purely ectothermic reptilian model of oxygen consumption, these inferred estimates of DMR should fall between predicted and measured values of reptilian resting and field metabolic rates, as well as being substantially lower than the FMR predicted for an endotherm of equivalent mass. Indeed, our behaviorally derived DMR estimates (mean=0.73+/-0.11 mL O(2) min(-1) kg(-1)) were 3.00+/-0.54 times the resting metabolic rate measured in unrestrained leatherbacks and 0.50+/-0.08 times the average FMR for a reptile of equivalent mass. These DMRs were also nearly one order of magnitude lower than the FMR predicted for an endotherm of equivalent mass. Thus, our findings lend support to the notion that diving leatherback turtles are indeed ectothermic and do not demonstrate elevated metabolic rates that might be expected due to regional endothermy. Their capacity to have a warm body core even in cold water therefore seems to derive from their large size, heat exchangers, thermal inertia, and insulating fat layers and not from an elevated metabolic rate.

Allometric estimation of metabolic rate from heart rate in penguins

Studies of the relationship between heart rate ( f H) and rate of oxygen consumption ( V˙ O 2 ), which are then used to predict field metabolic rate, frequently fail to incorporate body mass as a predictive variable. This is a potentially important omission in the study of animals whose body mass fluctuates substantially during their annual cycle. In an attempt further to improve estimates of field metabolic rate from f H, we re-evaluated data on M b, f H and V˙ O 2 from previous studies of macaroni penguins ( Eudyptes chrysolophus) and king penguins ( Aptenodytes patagonicus) and derived a new relationship to integrate these three quantities. This relationship is at least as accurate and precise as previously determined relationships. We applied this same principle to published data on 11 of the 20 recognised penguin taxa to derive a relationship to predict V˙ O 2 from f H and M b in penguins of any species. This result has interesting implications in terms of reducing the logistical burden in studies of field metabolic rate.

Seasonal Differences in Field Metabolism, Water Requirements, and Foraging Behavior of Free-Living Aardwolves

Aardwolves occur in east-central and southern Africa in regions of arid and semiarid grasslands. In South Africa, they feed almost exclusively on the termite Trinervitermes trinervoides during the warmer months of the year, whereas on cold winter nights these insects remain belowground, unavailable to aardwolves. At this time aardwolves shift their foraging efforts to a less abundant termite species, Hodotermes mossambicus. This species provides less food for aardwolves, making the wintertime potentially a period of energy stress for them. In this study, we report the first estimates of field metabolism and water flux as determined by doubly labeled water for a myrmecophagous euthermic mammal. Specifically, we tested the hypotheses that a reduced basal metabolic rate and pulmocutaneous water loss lead to a conservative field metabolic rate (FMR) and water flux in free-living aardwolves during summer and winter. Further, we quantified the activity budget of aardwolves during summer and winter to construct a time–energy budget for them. We used knowledge of water flux in aardwolves and of the water content of their prey to construct a water budget during summer and winter, and to estimate the seasonal consumption of termites by aardwolves. During summer (November–January), aardwolves that averaged 7768 g in body mass had a CO2 production of 112.5 L CO2/d, equivalent to an energy expenditure of 2891.2 kJ/d. During winter (June–July), when body mass averaged 8543 g, CO2 production averaged 71.8 L CO2/d, which translates to an FMR of 1844.8 kJ/d. Water flux equaled 615 mL/d in summer, but only 292 mL/d in winter, a decrease of 53.1%. Aardwolves were active for an average of 8.77 h/d in summer, but only 4.05 h/d during winter. A time budget for active periods showed that aardwolves spent a significantly larger proportion of their active time feeding in summer than in winter (26.7 vs. 15.2%). In addition, males and females spent 12.6% of their time in winter in breeding activities such as courtship and copulation. For aardwolves in summer, our model estimated a DEE of 2370.5 kJ/d, whereas during winter it predicted a DEE of 2086 kJ/d. These values deviated from our estimates of FMR by −18% and +13.1%, respectively. From data on water flux and the water content of termites, we estimated that aardwolves consumed 222445 Trinervitermes per night during the summer. Using previously obtained data on foraging, we predicted that aardwolves consume 833 termites per patch with an intake rate of 33 termites per second while feeding. During winter, aardwolves consumed 5867 Hodotermes and 2515 Trinervitermes per night. Our estimate of gross energy consumption was 5616 kJ/d in summer and 3022 kJ/d in winter. Assuming an assimilation efficiency of 0.66, metabolizable energy intake would be 3707 kJ/d in summer and 1995 kJ/d in winter. These values exceed FMR measurements by +22% in summer and by +8.1% in winter. It appears that aardwolves were in positive energy balance during our measurements of FMR.

Dietary energetics of the insectivorous Mexican free-tailed bat (Tadarida brasiliensis) during pregnancy and lactation.

Stomach content analysis of 20 pregnant (x body mass=13.4 g) and 18 lactating (x body mass=11.5 g) female Tadarida brasiliensis revealed that the diet, expressed as percent volume, consists largely of lepidopterans, coleopterans, hymenopterans, and dipterans, in decreasing order of importance. We found no significant difference in the diet of pregnant and lactating females when expressed as percent volume. However, when expressed as percent frequency, proportionately more pregnant females fed on lepidopterans, coleopterans, and dipterans than did lactating bats, and proportionately more lactating females fed on hymenopterans. We found no significant differences in the percentages of water, lean dry mass, fat, and energy density in the stomach contents of pregnant and lactating females. Water in stomach contents averaged 62.7% and fat and lean dry mass averaged 22.2% and 15.2%, respectively (expressed as percentage of wet mass); energy density averaged 31.2 kJ g-1 dry mass. This relatively high energy density of stomach contents, as compared to whole insects, can be attributed to the consumption of insects high in fat (especially flying ants) and the abdomens only of moths and beetles (other body parts being discarded). Estimates of nightly food intake increased markedly from mid- to late pregnancy, stabilized or decreased during late pregnancy, and increased again during early to mid-lactation. Average nightly feeding rate doubled from pregnancy to lactation and increased threefold during the first half of lactation. By adjusting our gravimetric estimates of nightly feeding rate upwards by 40% (based on estimates of field metabolic rate), we estimate that the average nightly energy intake of female T. brasiliensis ranges from 57 kJ day-1 in early lactation to 104 kJ day-1 in mid-lactation. These estimates represent nightly feeding rates averaging 39% and 73% of a female's body mass in the period from early to mid-lactation, respectively.

Seed predation by nocturnal rodents in an African savanna ecosystem

The small mammal community in Acacia savanna consists of three omnivorous nocturnal rodent species, Mastomys natalensis, Saccostomus campestris and Aethomys chrysophilus, which eat varying proportions of seed in their diet. From a seed removal experiment, it was found that rodents preferentially selected Acacia tortilis seeds. The annual Acacia seed consumption by rodents in a South African savanna ecosystem was analysed by using estimates of rodent population densities, diet composition, seed predation by captive rodents and published estimates of field metabolic rates. Total seed consumption was estimated to represent 1,64,1% of the annual seed crop of A. torlilis, 0,7-0,9% of the annual seed crop of A. nilotica and 9,3-25,0% of the annual seed crop of A. karroo. Granivory of A. nilotica seeds by rodents may have a negligible effect upon seedling recruitment. However, rodent predation of A. torlilis and A. karroo seeds may have important implications on seed survival and later seedling recruitment.

Field metabolic rates of instrumented Ad�lie penguins using double-labelled water

Adelie penguins (Pygoscelis adeliae) carrying dummy instruments were used to determine field metabolic rates using double-labelled water. All penguins injected with double-labelled water showed a marked loss of body mass (-4.5%) during the period of the experiments (20–131 h), irrespective of the time of the breeding season. Total body water averaged 57.3% and water flux estimates of field metabolic rates correlated with double-labelled water estimates of field metabolic rate (r2=0.68), indicating that Adelie penguins do not ingest significant amounts of sea water. Brooding Adelie penguins had a mean field metabolic rate of 10.1 W·kg-1 and at sea a field metabolic rate of 13.3 W·kg-1, both of which compare well with previously published estimates based on time/activity budgets and respirometry. Mean field metabolic rate in penguins with creching chicks was 14.1 W·kg-1, and the birds spent 65 h absent from the nest as opposed to previous estimates of 7.1 W·kg-1 and 21 h. The effects of weather, disturbance and manipulation on the behaviour and field metabolic rate of penguins late in the breeding season are discussed. Adelie penguins (creching chicks) equipped with externally attached instruments spent more time absent from the nest than noninstrumented controls (76 vs 54 h), but had a lower field metabolic rate.

Small mammal seed consumption in the Karoo, South Africa: further evidence for divergence in desert biotic processes

Annual seed consumption by a small mammal community in the semi-arid Karoo, South Africa, was calculated using population, biomass and dietary estimates and published estimates of field metabolic rate. The community comprised a macroscelid elephant shrew Macroscelides proboscideus, and two rodents Gerbillurus paeba and Desmodillus auricularis. Only G. paeba consumed seed during the study, and then in low amounts (annual mean = 0.4% of diet, insects = 53%, herbage = 47%), with M. proboscideus and D. auriocularis consuming mainly insects (88%) and herbage (90%), respectively. Energy requirements for the G. paeba population averaged 568 kJ ha-1 day-1. Total seed consumption was estimated to be ≈ 140 g ha-1, or 155 000 seeds ha-1 which represents ≈0.5% of the annual seed production for this site. These levels of granivory by small mammals are significantly lower than those recorded for North American deserts, and raises the question as to why granivory varies between these systems. These findings also refute the hypothesis that as a result of the harshness and similarity of physical conditions in deserts, the properties of desert communities are convergent.

Field Bioenergetics: Accuracy of Models and Methods

Doubly labeled water (DLW) estimates of field metabolic rates (M) and feeding rates (I) in free-living terrestrial vertebrates should be accurate to within ± 119%. In comparison with simultaneous DLW measurements, time-energy budget (TEB) determinations of M may be more than 40% too low, 55% too high, or very accurate. No one TEB model tested to date has been accurate in all cases. To yield reliable results, future TEB studies of small endotherms should include field measurements of operative temperature (Te) and wind speed, and fresh laboratory measurements of the energetic costs of various activities should be done. The assimilation method for estimating I involves field measurements of production (growth and reproduction, or population mortality) along with estimates of M in the field, and it yielded reasonable results in one study on lizards. The field feces collection method has yielded apparent underestimates of I in two situations. The radiosodium turnover technique for measuring I is promising for animals having simple diets, and this method should be tested under field conditions. Potentially, the most profitable approach in field bioenergetics studies is the inclusion of several of these methods simultaneously, so that one method may cover for the shortcomings of another, and the results will be richly detailed.