Mean Field Metabolic Rate Research Articles

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.

Energetic demands of immature sea otters from birth to weaning: implications for maternal costs, reproductive behavior and population-level trends.

Sea otters (Enhydra lutris) have the highest mass-specific metabolic rate of any marine mammal, which is superimposed on the inherently high costs of reproduction and lactation in adult females. These combined energetic demands have been implicated in the poor body condition and increased mortality of female sea otters nearing the end of lactation along the central California coast. However, the cost of lactation is unknown and currently cannot be directly measured for this marine species in the wild. Here, we quantified the energetic demands of immature sea otters across five developmental stages as a means of assessing the underlying energetic challenges associated with pup rearing that may contribute to poor maternal condition. Activity-specific metabolic rates, daily activity budgets and field metabolic rates (FMR) were determined for each developmental stage. Mean FMR of pre-molt pups was 2.29 ± 0.81 MJ day(-1) and increased to 6.16 ± 2.46 and 7.41 ± 3.17 MJ day(-1) in post-molt pups and dependent immature animals, respectively. Consequently, daily energy demands of adult females increase 17% by 3 weeks postpartum and continue increasing to 96% above pre-pregnancy levels by the average age of weaning. Our results suggest that the energetics of pup rearing superimposed on small body size, marine living and limited on-board energetic reserves conspire to make female sea otters exceptionally vulnerable to energetic shortfalls. By controlling individual fitness, maternal behavior and pup provisioning strategies, this underlying metabolic challenge appears to be a major factor influencing current population trends in southern sea otters (Enhydra lutris nereis).

Seasonally constant field metabolic rates in free-ranging sugar gliders ( Petaurus breviceps)

Sugar gliders, Petaurus breviceps (average body mass: 120 g) like other small wild mammals must cope with seasonal changes in food availability and weather and therefore thermoregulatory and energetic challenges. To determine whether free-ranging sugar gliders, an arboreal marsupial, seasonally adjust their energy expenditure and water use, we quantified field metabolic rates (FMR) and water flux at a seasonal cool-temperate site in eastern Australia. Thirty six male and female sugar gliders were labelled with doubly labelled water for this purpose in spring, summer and autumn. The mean FMR was 159 ± 6 kJ d − 1 (spring), 155 ± 8 kJ d − 1 (summer), and 152 ± 20 kJ d − 1 (autumn) and the mean FMR for the three seasons combined was 158 ± 5 kJ d − 1 (equivalent to 1.33 kJ g − 1 d − 1 or 780 kJ kg − 0. 75 d − 1 ). The mean total body water was 83 ± 2 g, equal to 68.5% of body weight. Mean water flux was 29 ± 1 mL day − 1 . Season, ambient temperature or sex did not affect any of the measured and estimated physiological variables, but body mass and total body water differed significantly between sexes and among seasons. Our study is the first to provide evidence for a constant FMR in a small mammal in three different seasons and despite different thermal conditions. This suggests that seasonal changes in climate are compensated for by behavioural and physiological adjustments such as huddling and torpor known to be employed extensively by sugar gliders in the wild.

The cold shoulder: free-ranging snowshoe hares maintain a low cost of living in cold climates

The hypothesis that cold air temperatures (Ta) constrain the metabolic diversity of high-latitude endotherms is based on the observation among birds and mammals that mean field metabolic rate (FMR) increases, whereas the variability of FMR decreases, from the warm tropics to the cold poles. However, there is a paucity of FMR measurements from above 60° latitude and below 0 °C. We measured the daily energy expenditure of a high-latitude population of free-ranging snowshoe hares ( Lepus americanus Erxleben, 1777) in Yukon, Canada, in winter (Ta-mean = –16.4 °C) and in autumn (Ta-mean = 0.5 °C). Doubly labelled water measures of FMR were approximately 20% lower in winter than in autumn, and were a similar, low multiple of resting metabolic rate in both seasons (2.04 and 1.94, respectively). The mass-corrected FMR of snowshoe hares in winter was only half the value predicted by extrapolating the relationship between FMR and Ta > 0 to –16.4 °C. These results contribute to an emerging pattern of a reversal in the relationship between FMR and Ta in free-ranging mammals from negative above 0 °C to positive below 0 °C. We refer to the positive, low Ta portion of this relationship as the cold shoulder, and suggest that it may reflect the general necessity for free-ranging mammals to use behavioural and (or) physiological means to conserve energy during long winters when cold conditions coincide with resource scarcity.

Diving and foraging energetics of the smallest marine mammal, the sea otter (Enhydra lutris)

As the smallest and one of the most recently evolved marine mammals, sea otters face physiological challenges rarely encountered by larger, more derived aquatic species. To examine the effect of these challenges on foraging costs and resultant daily energy budgets, we measured the energetics of resting, grooming, diving and foraging for adult, male sea otters. The energy expended for these different behaviors as determined from open flow respirometry was then standardized across activity budgets measured for wild sea otters to estimate field metabolic rates (FMR). We found that the metabolic rate of captive otters performing single dives ranging in duration from 40 to 192 s was 17.6+/-0.5 ml O(2) kg(-1) min(-1) and only 1.3 times resting rates. This rate increased significantly if the animals foraged during submergence. The cost of a foraging dive for sea otters was nearly twice that predicted for phocid seals, which was attributed in part to elevated locomotor costs associated with buoyancy and swimming style. Our behavioral studies indicate that wild sea otters spend the greatest proportion of the day feeding and resting, with the largest daily energy expenditure (6.1+/-1.1 MJ day(-1)) associated with foraging. The resulting mean FMR for wild sea otters based on the energy expended for all behaviors was 15.7+/-2.7 MJ day(-1) and matched predicted FMR values based upon a regression of known FMR values for other marine mammals across a range of body sizes. This was achieved by counterbalancing elevated foraging costs with prolonged periods of rest on the water surface.

Seasonal metabolism of juvenile green turtles (Chelonia mydas) at Heron Island, Australia

We investigated seasonal changes in the energetics of juvenile green turtles (Chelonia mydas (L., 1758)) (9.8–23.8 kg) from a resident population on the southern Great Barrier Reef. Doubly labeled water was used to determine water flux and field metabolic rate (FMR) of green turtles during summer (mean water temperature (TW) = 25.8 °C) and winter (mean TW = 21.4 °C), and muscle tissue was collected for analysis of thermal sensitivity of metabolic enzyme activity. There was no significant seasonal difference in total body water (TBW) content (73.7% and 75.1% of body mass in summer and winter, respectively) or water flux (7.5% and 6.1% of TBW per day in summer and winter, respectively). The mean FMR during winter (81 ± 15 kJ·kg–1·d–1) was 43% lower than that during summer (142 ± 33 kJ·kg–1·d–1), but the seasonal difference in FMR marginally failed to reach statistical significance (P = 0.17). Thermal dependence of citrate synthase, lactate dehydrogenase, and pyruvate kinase activity was relatively low (Q10 = 1.20–1.68) over the range of temperatures experienced by turtles during summer and winter, and there were no significant seasonal differences in enzyme activity. In summary, juvenile green turtles experience only moderate changes in metabolism within the temperature range and environmental conditions experienced seasonally at this subtropical site.

Influences of winter supplemental feeding on the energy balance of white-tailed deer fawns in New Hampshire, U.S.A.

The purpose of this study was to determine the influence of supplemental feeding on the energy balance of white-tailed deer (Odocoileus virginianus) in northern New Hampshire, U.S.A., during January–March 1997. We measured the field metabolic rate (FMR) and energy balance of 10 (5 males and 5 females) supplementally fed wild fawns with doubly labeled water over 19–21 days. We tested whether percent acid detergent fiber (ADF) and percent neutral detergent fiber in deer fecal samples predicted the proportion of supplemental feed (pelleted concentrate) in the diet of deer. The mean FMR of fawns was 758.4 kJ·kg–0.75·d–1 (range = 535.9–1032.8 kJ·kg–0.75·d–1), or 2 × their basal metabolic rate (BMR). The mean FMR of male fawns was >30% higher than that of female fawns. Percent body fat (12.1 ± 1.4% (mean ± SE)) and mass loss (3.0 ± 0.9%) varied among fawns, suggesting that an individual high FMR was not detrimental to energy balance and was related to availability of feed. We estimated that a high FMR (>2 × BMR) could be maintained only if fawns consumed about 1 kg of supplemental feed daily. Radiotelemetry data indicated that the number and juxtaposition of feeding sites in an area probably influenced home range and activity of deer. Percent ADF in feces provided the best prediction of percent grain in the diet (% grain = –0.048(% ADF)2 + 1.523(% ADF) + 96.467; r2 = 0.69) and was useful for identifying populations consuming supplemental pelleted concentrate. Biologists should expect that the influence of winter feeding on energy balance and survival will vary according to the interrelationships of deer density, food availability, and winter severity at feeding sites.

Field metabolic rate of lactating female Galápagos fur seals ( Arctocephalusgalapagoensis): the influence of offspring age and environment

Galápagos fur seals, Arctocephalus galapagoensis, live in a seasonal environment which varies strongly in productivity from year to year. We measured how the field metabolic rates (FMR) of lactating females varied with season, pup age and year. Energy expenditure was measured using doubly labeled water (DLW) during the cold seasons of 1984 and 1985 in 9 mothers of 1–3-month-old pups and 5 mothers of yearlings, and during the 1986 warm season in 8 mothers of 6-month-old pups. Young pups gained 0.84% mass/day during the cold season, but larger pups during the warm season lost 1.25% mass/day. During the warm season, females had lower relative total body water than during the cold season suggesting higher fat content during the warm, less productive season, but the effect was even more marked when comparing different years of the study: fat content was high in 1984 and 1986 and low in 1985. The FMR of mothers varied from 134 to 167 W but did not show significant differences between any of the pup age-groups. Among the years of the study, FMR showed only a trend towards low energy expenditure of mothers of young pups in 1984. The mean FMR was lower than for other otariids. Mothers may limit energy expenditure independent of pup age and season to minimize their own risk of starvation in an environment of comparatively low productivity, varying unpredictably due to frequent El Niño events.

Individual variation in field metabolic rate of kittiwakes (Rissa tridactyla) during the chick-rearing period.

Field metabolic rate (FMR), using the doubly labelled water (DLW) method, was measured in free-ranging adult kittiwakes (Rissa tridactyla) early and late in the chick-rearing period at Svalbard, Norway. Individual variation in FMR was analysed by comparing FMR with body mass, sex, nest attendance, chick age, brood size, and basal metabolic rate (BMR). Mean FMR of kittiwakes during the chick-rearing period was 27.0+/-0.9 (SE) W kg(-1), while the individual variation (calculated as coefficient of variation [CV]) in FMR was 24%. Sex, time spent away from the nest, age of the chicks, and brood size contributed significantly to FMR and explained 65% of the variation in FMR. The FMR increased by 32% from early until late in the chick-rearing period. This occurred simultaneously with an increase in the time spent away from the nest. In 15 of 20 pairs, one of the mates had 15% or higher (mean of the 15 pairs, 22%+/-8%) FMR (W kg(-1)) than their partner, even though the mates spent equal amounts of time away from the nest. This indicates an intrapair conflict in FMR. The variation in total FMR of pairs was 40% less than the individual variation, and total FMR of pairs increased with age of the chicks. This indicates that the mates adjust their energy expenditure within a relatively constant FMR determined by the energy needs of the chicks. Individual variation in FMR could not be explained by variation in body mass or BMR. BMR measured late in the chick-rearing period was 26% lower than previous measurements of BMR from the prebreeding and incubation periods. The increase in FMR and simultaneous decrease in BMR caused a 40% increase in metabolic intensity (FMR/BMR) of kittiwakes during the chick-rearing period. It is suggested that the metabolic intensity is not a proper measure of the metabolic load in seabirds.

Seasonal field energetics and water influx rates of the greater bilby (Macrotis lagotis)

Water and energy requirements of free-living male and female greater bilbies (Macrotis lagotis) were measured over two summers and two winters on Astrebla Downs National Park in far south-western Queensland, Australia, by means of the doubly labelled water method. Mean water influx rate of the bilby (mean body mass: summer 928 g; winter 848 g) did not differ between summer (63.1 mL day–1) and winter (53.1 mL day–1), but mean field metabolic rate was significantly higher during summer (617.2 kJ day–1) than in winter (480.3 kJ day–1). The comparatively low water influx rate of the bilby (significantly lower than that predicted for a 887-g marsupial: P < 0.001) indicated that bilbies have the ability to conserve water in the wild. In contrast, field metabolic rate of the bilby did not differ significantly from that predicted for a marsupial of its body mass (P = 0.999). Bilbies were able to obtain sufficient food and water to satisfy energy and water requirements in three out of the four study periods. However, they were in negative energy and water balance during one study period, suggesting that they are susceptible to nutrient and water stress. The relatively low body fat stores of bilbies in the wild also indicate that they are vulnerable to periods of low food availability. The metabolic strategies of the bilby are only partly suggestive of adaptation to arid conditions.

Field metabolic rate of wild turkeys in winter

We investigated the winter bioenergetics of eastern wild turkeys (Meleagris gallopavo sylvestris) by measuring standard metabolic rate (SMR) and existence metabolism (EM) of captive turkeys and field metabolic rate (FMR) of free-ranging turkeys. Mean SMR and EM were 0.511 ± 0.040 mL O2·g-1·h-1 and 499.7 ± 17.7 kJ·kg body mass-0.734·d-1 (mean ± SE) as measured by indirect respirometry and food consumption, respectively. FMR was measured with doubly labeled water and was 10.5% higher in juvenile (0.976 ± 0.039 L CO2·kg-0.734·h-1) than adult turkeys (0.883 ± 0.034 L CO2·kg-0.734·h-1); their FMR:SMR ratios were 1.74 and 1.58, respectively. Juvenile turkeys weighed less and had less body fat (13.5%) than adults (18.9%). Mean FMR was lowest in 1996, when ground forage was unavailable and weather was more windy and cold than in 1995, when ground forage was available and the turkeys' activity and range were greater. Turkeys reduced FMR in 1996 by restricting movement and range, and using proximate shelter and supplemental food. We predict that juvenile turkeys are at an energetic disadvantage when food availability is restricted because of their higher FMR, lower body and fat masses, and higher activity costs than adults.

Seasonal metabolism of a small, arboreal monitor lizard, Varanus scalaris, in tropical Australia

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%).

Energy Expenditure of Female Barn Swallows Hirundo rustica during Egg Formation

The energy expenditure of female barn swallows (Hirundo rustica) was measured during the period of egg formation using the doubly labelled water (DLW) technique. Mean field metabolic rate (FMR) was 104-112 kJ d⁻¹ (standard deviation [ SD] = 22, n = 12), dependent on assumptions used in the calculations. The energy expenditure of female swallows did not differ significantly between egg formation, incubation, and nestling-rearing periods. Water turnover rate of laying females was 18.4 mL d⁻¹ (SD = 2.0, n = 12). The amount of egg material deposited during energy expenditure measurements was determined for 11 of the birds by feeding them lipophilic dye, which marked the outside of each rapidly developing ovarian follicle. The energy content of egg material deposited in 24 h averaged 4.9 kJ (SD = 2.3, n = 11), which represented 4.5%-4.9% of FMR. Variation in FMR was not correlated with egg deposition. The mean clutch size of swallows for which FMR was measured during egg formation was slightly but significantl...

Energetics and Water Flux in a Semiaquatic Lizard, Varanus mertensi

Varanus mertensi is a semiaquatic lizard that lives near permanent water in northern Australia. During the wet and dry seasons, we measured the field metabolic rate (FMR) and water flux rates of animals in the field and standard metabolic rates across a range of body temperatures (18-36 C) in the laboratory. We combined these data to divide the FMR into energy expended during periods of rest and activity. The FMR was significantly higher in the wet season (120.7 kJ kg-' day-') than in the dry season (81.1 kJ kg-' day-'). There was no difference in the water flux rate between the wet (63.2 ml kg-' day-') and dry (66.5 ml kg-' day-') seasons. The FMR during the wet season is greater than that predicted for a similarly sized iguanid lizard, but the 95% confidence interval around the mean FMR in the dry season overlaps the predicted iguanid value. The calculated percent of the FMR devoted to activity is high for both seasons (70-73%) com- pared to other lizards, as is the calculated sustainable metabolic scope (3.4-3.7). When compared to terrestrial varanid lizards living in the same area during their active seasons, V. mertensi does not show any quantitative differences in FMR or water flux. Varanus mertensi does differ from these terrestrial species in not having an inactive period during the dry season, and we suggest that this is related to the continual availability of food and water in its habitat.

Water and Energy Balance of Captive and Free-Ranging Spinifexbirds (Eremiornis Carteri) North (Aves:Sylviidae) on Barrow Island, Western Australia

The mean annual rainfall of Barrow Island, located about 90 km north of Onslow off the arid Western Australian coast, is 324 mm, 74% of which falls as cyclonic rain between February and May. Spinifexbirds captured in May 1992 had a mean body mass of 12.3 +/- 0.3 g and a total body water content (TBW) of 774 +/- 1.6%. In December 1992 the mean body mass was significantly lower (11.7 +/- 0.2 g; P < 0.05), despite a TBW of 73.4 +/- 1.0%. Spinifexbirds maintained water balance in both seasons, but water flux rates were significantly higher in May (P = 0.01). Respective influx and efflux rates in May were 0.70 +/- 0.30 and 0.72 +/- 0.03 mL (g day)(-1) compared with 0.60 +/- 0.04 and 0.57 +/- 0.04 mL (g day)(-1) in December. Field metabolic rates (FMRs), measured with doubly-labelled water ((3)HH(18)0), did not differ significantly between the two periods. The mean FMR in May was 6.8 +/- 0.6 mL CO2 (g h)(-1) compared with 7.2 +/- 0.9 mL CO2 (g h)(-1) in December, similar to rates predicted by Nagy and Peterson (1988) for a similar-sized passerine. The thermoneutral zone (TNZ) of spinifexbirds, determined by metabolic laboratory trials in December, extended from 30 to 39 degrees C. The standard metabolic rate (SMR) within the TNZ was 2.9 +/- 0.1 mL O-2 (g h)(-1), which is up to 20% lower than predicted values. Body temperature was maintained at 39.1 degrees C in the TNZ, but birds became hyperthermic at ambient temperatures (T(a)s) higher than 35 degrees C, with body temperatures reaching 44 degrees C. Wet thermal conductance and evaporative water loss increased markedly at T(a)s > 35 degrees C. The data suggest that spinifexbirds have limited physiological adaptations to desert conditions compared with some other arid-zone birds.

Flight Energetics of Free-Ranging Red-Footed Boobies (Sula sula)

Flight energetics of free-ranging red-footed boobies (Sula sula) on Johnston Atoll in the central Pacific Ocean were quantified using doubly labeled water to measure field metabolic rate (FMR), an open-flow system to measure O₂ consumption rate, and activity recorders to monitor foraging behavior at sea. Brooding birds spent an average of 496% ± 6% of the time at the nest, 6% ± 2% of the time sitting on the water, and 41% ± 7% of the time in flight. Mean FMR was 14.2 ± 1.2 W (n = 9; mean mass = 1,070 ± 40.3 g). Mean resting metabolic rate was 9. 7 ± 0.7 W (n = 8: mean mass = 1,039 ± 25.8 g). The power required for flight averaged 19.0 ± 3.4 W (n = 6; mean mass = 1, 014 ± 42 g). This was less than one-third of the predicted value (62.1 W) obtained from equations based on aerodynamic theory. Aerodynamic theory predicts that birds in this study would require a mean of 0.5 ± 0.01 m s−1 of lift in order to be able to soar. Wind velocity during the period of FMR measurement averaged more than 10 times this, 5.7 ± 0.3 m s−1. Thus, this striking difference between measured andpredicted cost of flight is likely due to the ability of birds to soar, and, in fact, observations of red-footed boobies at sea confirm that their flight includes a complex set of behaviors that probably serve to take advantage of wind energy and substantially lower their energetic cost of flight. More data are needed on flight behavior patterns of birds at sea.

Foraging Radii and Energetics of Least Auklets (Aethia pusilla) Breeding on Three Bering Sea Islands

We studied the relationship between the foraging radius and energy economy of least auklets (Aethia pusilla) breeding in colonies on three islands in the Bering Sea (St. Lawrence, St. Matthew, and St. George Islands). The distance to which auklets commuted on foraging trips varied by more than an order of magnitude (5-56 km), but mean field metabolic rate (FMR) did not vary significantly among birds from the three islands. These observations indicate that allocation to various compartments of time and energy budgets is flexible and suggest that least auklets may have a preferred level of daily energy expenditure that is similar across colonies. We modeled the partitioning of energy to various activities and hypothesize that the added cost of commuting incurred by auklets from St. Lawrence Island (foraging radius, 56 km) was offset by reduced energy costs while foraging at sea. Data on bird diets and prey abundances indicated that auklets from St. Lawrence Island fed on larger, more energy-rich copepods than did auklets from St. Matthew Island (foraging radius, 5 km) but that depth-averaged prey density did not differ significantly between the birds' principal foraging areas. However, previous studies have indicated that zooplankton abundance is vertically compressed into near-surface layers in stratified waters off St. Lawrence Island, which suggests that variation in foraging eficiency may have resulted in part from differences in the accessibility of food rather than its absolute abundance in the water column. Our findings demonstrate why long-distance commuting between colony and feeding areas need not significantly affect total daily adult energy expenditures, even in heavily wing-loaded species such as auklets. Interpretation of the energetic ecology of auklets and other seabirds can strongly benefit from information regarding foraging distributions, diets, and prey accessibility.

Consumption of Atlantic salmon smolts and parr by goosanders: estimates from doubly‐labelled water measurements of captive birds released on two Scottish rivers

The field metabolic rates (FMRs) of nine captive goosanders, Mergus merganser, released on two Scottish rivers were estimated using the doubly‐labelled water (DLW) technique. Mean (± S.E.) FMR was 2.322±0.239ml CO2 g−1 h−1 and daily energy expenditure (DEE) 1939 ± 184 kJ per day. This was significantly greater (x 1.5) than previous estimates which assumed DEE to be three times the basal metabolic rate (BMR) based on regression equations predicting BMR from body mass. FMR of captives and dietary data from previous studies were used to estimate daily consumption of salmon, Salmo salar, smolts and parr by natural populations of these ducks on the river North Esk, north‐east Scotland. Goosanders are likely to consume 480‐522 g fish per day of which two‐thirds are juvenile salmon; equivalent to a daily intake of 10‐11 smolts and 48‐52 parr. Annual predation of smolts by goosanders was estimated to be between 8000 and 15 000 or 3 and 16% of annual production.

Field metabolic rate in two species of shrew-tenrec, Microgale dobsoni and M. talazaci

Doubly labelled water (DLW) was used to determine field metabolic rate (FMR) in the shrew-tenrecs Microgale dobsoni and M. talazaci. Measures were obtained on six animals in their natural habitat and on five individuals in captivity. Mean FMR for nonreproducing M. dobsoni (mean body mass 42.6 ± 1.7 g) was 77.1 ± 3.2 kJ/d (CV = 53.7%, N = 4), 3.8 times resting metabolic rate (RMR). Mean FMR for nonreproducing M. talazaci (mean body mass 42.8 ± 4.9 g) was 66.5 ± 14.1 kJ/d (CV = 51.9%, N = 6), 3.2 times RMR. FMR within each species was not significantly correlated with body mass. This may in part reflect the large variation among individuals combined with the small sample size. FMR in shrew-tenrecs was within the range of FMR found in similar sized rodents, although variation was greater in the tenrecs. The high variability of FMR within the Tenrecidae may be a result of variations in body temperature. FMR/RMR ratios for both species fell within the range determined for other small mammals. The present study therefore offers further evidence to support a relationship between FMR and RMR.

Use of Physiological Telemetry as a Method of Estimating Metabolism of Fish in the Natural Environment

Abstract One of the most difficult components to measure in the energy budgets of natural fish populations is the energy released in metabolism. Telemetry of physiological correlates of metabolism, such as heart rate, can (with calibration) enable direct measurements of metabolism and simultaneous observations of behavior in the natural environment. Heart rate is a good indicator of metabolic rate for northern pike Esox lucius and was used to obtain information on metabolism, activity, and food intake in the natural environment. Mean field metabolic rates were 1.5 times standard metabolic rate. Activity metabolism accounted for 5–10% of total metabolism and was approximately an order of magnitude greater than estimates based on mean swimming speed derived from location tracking. Feeding metabolism was 15–25% of total metabolism. Even when the full metabolic rate calibration is not considered. physiological telemetry can provide useful information on patterns of energy expenditure ofdirect relevance to bio...