Modeling the marine resources consumed in raising a king penguin chick: an energetics approach.

Accurate estimates of penguin energetics would represent an important contribution to our understanding of the trophodynamics of the Southern Ocean ecosystem and our ability to predict effects of environmental change on these species. We used the heart rate-rate of oxygen consumption technique to estimate rate of energy expenditure in adult king penguins raising a chick, in combination with data from the literature on changes in adult mass, chick energy requirements, and prey energy density. Our model estimated a variety of energetic costs and quantities of prey consumption related to raising a king penguin chick during the austral summer. The total energy requirements of a king penguin chick at the Crozet Archipelago from hatching until reaching a mass of 8 kg 90 d later is 271 MJ, representing the consumption of 38.4 kg of myctophid fish. A successfully breeding male requires 0.78 kg d(-1) of fish during the entirety of the incubation period and 1.14 kg d(-1) during the subsequent 90 d of chick rearing. Assuming the same energy requirements for females, the estimated 580,000 pairs of king penguins that breed successfully at Crozet each year, together with their chicks, consume a total of around 190,000 tons of fish during the incubation and summer rearing periods combined. If, due to depletion of fish stocks, the diet of breeders and chicks during the summer becomes identical to the typical diet of adults during the austral winter, the mass of prey required by both adults and chicks combined (where the chick still reaches 8 kg after 90 d) would increase by more than 25%.

Recovery from swimming-induced hypothermia in king penguins: effects of nutritional condition.

We investigated changes in the rate of oxygen consumption (V O2) and body temperature of wild king penguins (Aptenodytes patagonicus) in different nutritional conditions during recovery after exposure to cold water. Over time, birds undertook an identical experiment three times, each characterized by different nutritional conditions: (1) having recently completed a foraging trip, (2) after fasting for many days, and (3) having been refed one meal after the fast. The experiments consisted of a 2-h session in a water channel followed by a period of recovery in a respirometer chamber on land. Refed birds recovered significantly more quickly than fed birds, in terms of both time to reach resting V O2 on land and time to reach recovery of lower abdominal temperature. Previous work found that when penguins are in cold water, abdominal temperatures decrease less in refed birds than in fed or fasted birds, suggesting that refed birds may be vasoconstricting the periphery while perfusing the gut region to access nutrients. This, alongside an increased resting [V O2], seems the most reasonable explanation for why refed birds recovered more quickly subsequent to cold-water exposure in this study; that is, vasoconstriction of the insulative periphery meant that they lost less heat generated by the body core.

Behavioral and physiological significance of minimum resting metabolic rate in king penguins.

Because fasting king penguins (Aptenodytes patagonicus) need to conserve energy, it is possible that they exhibit particularly low metabolic rates during periods of rest. We investigated the behavioral and physiological aspects of periods of minimum metabolic rate in king penguins under different circumstances. Heart rate (f(H)) measurements were recorded to estimate rate of oxygen consumption during periods of rest. Furthermore, apparent respiratory sinus arrhythmia (RSA) was calculated from the f(H) data to determine probable breathing frequency in resting penguins. The most pertinent results were that minimum f(H) achieved (over 5 min) was higher during respirometry experiments in air than during periods ashore in the field; that minimum f(H) during respirometry experiments on water was similar to that while at sea; and that RSA was apparent in many of the f(H) traces during periods of minimum f(H) and provides accurate estimates of breathing rates of king penguins resting in specific situations in the field. Inferences made from the results include that king penguins do not have the capacity to reduce their metabolism to a particularly low level on land; that they can, however, achieve surprisingly low metabolic rates at sea while resting in cold water; and that during respirometry experiments king penguins are stressed to some degree, exhibiting an elevated metabolism even when resting.

Do seasonal changes in metabolic rate facilitate changes in diving behaviour?

Macaroni penguins were implanted with data loggers to record heart rate (fH), abdominal temperature (Tab) and diving depth during their pre-moult trip (summer) and winter migration. The penguins showed substantial differences in diving behaviour between the seasons. During winter, mean and maximum dive duration and dive depth were significantly greater than during summer, but the proportion of dives within the calculated aerobic dive limit (cADL) did not change. Rates of oxygen consumption were estimated from fH. As winter progressed, the rate of oxygen consumption during dive cycles (sVO2DC)) declined significantly and mirrored the pattern of increase in maximum duration and depth. The decline in sVO2DC) was matched by a decline in minimum rate of oxygen consumption (sVO2min)). When sVO2min) was subtracted from sVO2DC), the net cost of diving was unchanged between summer and winter. We suggest that the increased diving capacity demonstrated during the winter was facilitated by the decrease in sVO2min). Abdominal temperature declined during winter but this was not sufficient to explain the decline in sVO2min). A simple model of the interactions between sVO2min), thermal conductance and water temperature shows how a change in the distribution of fat stores and therefore a change in insulation and/or a difference in foraging location during winter could account for the observed reduction in sVO2min) and hence sVO2DC).

Factorial aerobic scope is independent of temperature and primarily modulated by heart rate in exercising Murray cod (Maccullochella peelii peelii).

Several previous reports, often from studies utilising heavily instrumented animals, have indicated that for teleosts, the increase in cardiac output (Vb) during exercise is mainly the result of an increase in cardiac stroke volume (V(S)) rather than in heart rate (fH). More recently, this contention has been questioned following studies on animals carrying less instrumentation, though the debate continues. In an attempt to shed more light on the situation, we examined the heart rates and oxygen consumption rates (Mo2; normalised to a mass of 1 kg, given as Mo2kg) of six Murray cod (Maccullochella peelii peelii; mean mass+/-SE = 1.81+/-0.14 kg) equipped with implanted fH and body temperature data loggers. Data were determined during exposure to varying temperatures and swimming speeds to encompass the majority of the biological scope of this species. An increase in body temperature (Tb) from 14 degrees C to 29 degrees C resulted in linear increases in Mo2kg (26.67-41.78 micromol min(-1) kg(-1)) and fH (22.3-60.8 beats min(-1)) during routine exercise but a decrease in the oxygen pulse (the amount of oxygen extracted per heartbeat; 1.28-0.74 micromol beat(-1) kg(-1)). During maximum exercise, the factorial increase in Mo2kg was calculated to be 3.7 at all temperatures and was the result of temperature-independent 2.2- and 1.7-fold increases in fH and oxygen pulse, respectively. The constant factorial increases in fH and oxygen pulse suggest that the cardiovascular variables of the Murray cod have temperature-independent maximum gains that contribute to maximal oxygen transport during exercise. At the expense of a larger factorial aerobic scope at an optimal temperature, as has been reported for species of salmon and trout, it is possible that the Murray cod has evolved a lower, but temperature-independent, factorial aerobic scope as an adaptation to the largely fluctuating and unpredictable thermal climate of southeastern Australia.

Metabolism and thermoregulation during fasting in king penguins, Aptenodytes patagonicus, in air and water.

We measured oxygen consumption rate (Vo(2)) and body temperatures in 10 king penguins in air and water. Vo(2) was measured during rest and at submaximal and maximal exercise before (fed) and after (fasted) an average fasting duration of 14.4 +/- 2.3 days (mean +/- 1 SD, range 10-19 days) in air and water. Concurrently, we measured subcutaneous temperature and temperature of the upper (heart and liver), middle (stomach) and lower (intestine) abdomen. The mean body mass (M(b)) was 13.8 +/- 1.2 kg in fed and 11.0 +/- 0.6 kg in fasted birds. After fasting, resting Vo(2) was 93% higher in water than in air (air: 86.9 +/- 8.8 ml/min; water: 167.3 +/- 36.7 ml/min, P < 0.01), while there was no difference in resting Vo(2) between air and water in fed animals (air: 117.1 +/- 20.0 ml O(2)/min; water: 114.8 +/- 32.7 ml O(2)/min, P > 0.6). In air, Vo(2) decreased with M(b), while it increased with M(b) in water. Body temperature did not change with fasting in air, whereas in water, there were complex changes in the peripheral body temperatures. These latter changes may, therefore, be indicative of a loss in body insulation and of variations in peripheral perfusion. Four animals were given a single meal after fasting and the temperature changes were partly reversed 24 h after refeeding in all body regions except the subcutaneous, indicating a rapid reversal to a prefasting state where body heat loss is minimal. The data emphasize the importance in considering nutritional status when studying king penguins and that the fasting-related physiological changes diverge in air and water.

Heart rate and energetics of free-ranging king penguins (Aptenodytes patagonicus).

The main objective of this study was to determine heart rate (fh) and the energetic costs of specific behaviours of king penguins while ashore and while foraging at sea during their breeding period. In particular, an estimate was made of the energetic cost of diving in order to determine the proportion of dives that may exceed the calculated aerobic dive limit (cADL; estimated usable O2 stores/estimated rate of oxygen consumption during diving). An implanted data logger enabled fh and diving behaviour to be monitored from 10 free-ranging king penguins during their breeding period. Using previously determined calibration equations, it was possible to estimate rate of oxygen consumption (VO2) when the birds were ashore and during various phases of their foraging trips. Diving behaviour showed a clear diurnal pattern, with a mixture of deep (>40 m), long (>3 min) and shallow (<40 m), short (<3 min) dives from dawn to dusk and shallow, short dives at night. Heart rate during dive bouts and dive cycles (dive + post-dive interval) was 42% greater than that when the birds were ashore. During diving, fh was similar to the 'ashore' value (87+/-4 beats min(-1)), but it did decline to 76% of the value recorded from king penguins resting in water. During the first hour after a diving bout, fh was significantly higher than the average value during diving (101+/-4 beats min(-1)) and for the remainder of the dive bout. Rates of oxygen consumption estimated from these (and other) values of fh indicate that when at sea, metabolic rate (MR) was 83% greater than that when the birds were ashore [3.15 W kg(-1) (-0.71, +0.93), where the values in parentheses are the computed standard errors of the estimate], while during diving bouts and dive cycles, it was 73% greater than the 'ashore' value. Although estimated MR during the total period between dive bouts was not significantly different from that during dive bouts [5.44 W kg(-1) (-0.30, +0.32)], MR during the first hour following a dive bout was 52% greater than that during a diving bout. It is suggested that this large increase following diving (foraging) activity is, at least in part, the result of rewarming the body, which occurs at the end of a diving bout. From the measured behaviour and estimated values of VO2, it was evident that approximately 35% of the dives were in excess of the cADL. Even if VO2 during diving was assumed to be the same as when the birds were resting on water, approximately 20% of dives would exceed the cADL. As VO2 during diving is, in fact, that estimated for a complete dive cycle, it is quite feasible that VO2 during diving itself is less than that measured for birds resting in water. It is suggested that the regional hypothermia that has been recorded in this species during diving bouts may be at least a contributing factor to such hypometabolism.

Effect of fasting on the VO2-fh relationship in king penguins, Aptenodytes patagonicus.

King penguins (Aptenodytes patagonicus) may fast for up to 30 days during their breeding period. As such extended fasting may affect the relationship between the rate of O(2) consumption (Vo(2)) and heart rate (f(H)), five male king penguins were exercised at various speeds on repeated occasions during a fasting period of 24-31 days. In addition, Vo(2) and f(H) were measured in the same animals during rest in cold air and water (4 degrees C). Vo(2) and f(H) at rest and Vo(2) during exercise decreased with fasting. There was a significant relation between Vo(2) and f(H) (r(2) = 0.56) that was improved by including speed, body mass (M(b)), number of days fasting (t), and a cross term between f(H) and t (r(2) = 0.92). It was concluded that there was a significant change in the Vo(2)-f(H) relationship with fasting during exercise. As t is measurable in the field and was shown to be significant and, therefore, a practical covariate, a regression equation for use when birds are ashore was obtained by removing speed and M(b). When this equation was used, predicted Vo(2) was in good agreement with the observed data, with an overall error of 3.0%. There was no change in the Vo(2)-f(H) relationship in penguins at rest in water.

Energetics of diving in macaroni penguins.

Heart rate (fH), abdominal temperature (T(ab)) and diving depth were measured in thirteen free-ranging breeding female macaroni penguins. Measurement of these variables allowed estimation of the mass-specific rate of oxygen consumption (V(O(2))) while diving and investigation of the physiological adjustments that might facilitate the diving behaviour observed in this species. In common with other diving birds, macaroni penguins showed significant changes in fH associated with diving, and these variables accounted for 36% of the variation in dive duration. When V(O(2)) was calculated for dives of different durations, 95.3% of dives measured were within the calculated aerobic dive limit (cADL) for this species. Mean fH for all complete dive cycles was 147+/-6 beats min(-1). When this fH is used to estimate (O(2)) of 26.2+/-1.4 ml min(-1) kg(-1) then only 92.8% of dives measured were within the cADL. Significant changes in abdominal temperature were not detected within individual dives, though the time constant of the measuring device used may not have been low enough to record these changes if they were present. Abdominal temperature did decline consistently during bouts of repeated diving of all durations and the mean decrease in T(ab) during a diving bout was 2.32+/-0.2 degrees C. There was a linear relationship between bout duration and the magnitude of this temperature drop. There was no commensurate increase in dive duration during dive bouts as T(ab) declined, suggesting that macaroni penguins are diving within their physiological limits and that factors other than T(ab) are important in determining the duration of dives and dive bouts. Lowered T(ab) will in turn facilitate lower metabolic rates during diving bouts, but it was not possible in the present study to determine the importance of this energy saving and whether it is occurs actively or passively.

The energetics of barnacle geese (Branta leucopsis) flying in captive and wild conditions.

Experimental data on the relationship between mean heart rate (f(H)) and mean rate of oxygen consumption (VO(2)) of captive barnacle geese during flights in a wind tunnel are assessed in terms of their capacity to predict the typical VO(2) of wild barnacle geese, based on the recordings of their f(H), while undertaking autumn migratory flights between Spitsbergen (78 degrees N) and Caerlaverock, Scotland (55 degrees N). A significant linear relationship has been demonstrated between the f(H) and simultaneously recorded VO(2) of a single barnacle goose (B-B) flying in the wind tunnel (VO(2)=1.42 f(H)-304, r(2)=0.82, P<0.001, N=12 flights). Data recorded from three additional geese (N=4 flights), lay within the 95% prediction intervals of the relationship for goose B-B. When these geese (mean body mass=2.06 kg, n=4) were flown in the wind tunnel (WT) without the mask, they had a mean f(H) of 451+/-23 beats min(-1), yielding an estimate for VO(2) of 336+/-33 ml min(-1). However, f(H) has also been recorded from wild barnacle geese (mean migratory f(H) of 253 beats min(-1)), and substitution of this value into the above calibration equation results in an unrealistically low value for mean migratory VO(2) of only 55 ml min(-1). Various factors, such as differences in heart mass, selective tissue perfusion, environmental temperature and flock formation, which might account for some of the difference in f(H) between the captive and wild geese are discussed. Comparison with other WT studies shows that inter-species minimum mass-specific VO(2) declines with increasing body mass (M(b); range 0.035-2.8 kg) as 173 M(b)(-0.224), r(2)=0.848.

Heart rate and the rate of oxygen consumption of flying and walking barnacle geese (Branta leucopsis) and bar-headed geese (Anser indicus).

We tested the hypotheses that the relationship between heart rate (fH) and the rate of oxygen consumption ((O(2))) differs between walking and flying in geese and that fH and (O(2)) have a U-shaped relationship with flight speed. We trained barnacle geese Branta leucopsis (mean mass 2.1 kg) and bar-headed geese Anser indicus (mean mass 2.6 kg) to walk inside a respirometer on a treadmill and to fly in a wind tunnel with a respirometry mask at a range of speeds. We measured fH and (O(2)) simultaneously during walking on the treadmill in five individuals of each species and in one bar-headed goose and four barnacle geese during flight in the wind tunnel. The relationships between fH and (O(2)) were significantly different between flying and walking. (O(2)) was higher, and the increment in (O(2)) for a given increase in fH was greater, for flying than for walking geese. The relationship between fH and (O(2)) of free-living barnacle geese during their natural migratory flights must differ from that measured in the wind tunnel, since the fH of wild migratory birds corresponds to values of (O(2)) that are unrealistically low when using the calibration relationship for our captive birds. Neither fH nor (O(2)) varied with flight velocity across the range of speeds over which the geese would fly sustainably.

The heart rate/oxygen consumption relationship during cold exposure of the king penguin: a comparison with that during exercise.

This study investigated whether exposure to low ambient temperature could be used as an alternative to exercise for calibrating heart rate (fH) against rate of oxygen consumption ((O(2))) for subsequent use of fH to estimate (O(2)) in free-ranging animals. Using the relationship between the oxygen pulse (OP, the amount of oxygen used per heart beat) and an index of body condition (or nutritional index, NI), a relationship between fH and (O(2)) was established for resting king penguins exposed to a variety of environmental temperatures. Although there was a small but significant increase in the OP above and below the lower critical temperature (-4.9 degrees C), there was no difference in the relationship obtained between the OP and body condition (NI) obtained above or below the lower critical temperature. These results were then compared with those obtained in a previous study in which the relationship between fH and (O(2)) had been established for king penguins during steady-state exercise. The relationship between OP and NI in the present study was not significantly different from the relationship between resting OP and NI in the previous study. However, the relationship was different from that between active OP and NI. We conclude that, at least for king penguins, although thermoregulation does not affect the relationship between resting OP and NI, temperature cannot be used as an alternative to exercise for calibrating fH against (O(2)) for subsequent use of fH to estimate (O(2)) in free-ranging animals.

Heart rate as an indicator of oxygen consumption: influence of body condition in the king penguin.

The use of heart rate to estimate field metabolic rate has become a more widely used technique. However, this method also has some limitations, among which is the possible impact that several variables such as sex, body condition (i.e. body fat stores) and/or inactivity might have on the relationship between heart rate and rate of oxygen consumption. In the present study, we investigate the extent to which body condition can affect the use of heart rate as an indicator of the rate of oxygen consumption. Twenty-two breeding king penguins (Aptenodytes patagonicus) were exercised on a variable-speed treadmill. These birds were allocated to four groups according to their sex and whether or not they had been fasting. Linear regression equations were used to describe the relationship between heart rate and the rate of oxygen consumption for each group. There were significant differences between the regression equations for the four groups. Good relationships were obtained between resting and active oxygen pulses and an index of the body condition of the birds. Validation experiments on six courting king penguins showed that the use of a combination of resting oxygen pulse and active oxygen pulse gave the best estimate of the rate of oxygen consumption V(O2). The mean percentage error between predicted and measured V(O2) was only +0.81% for the six birds. We conclude that heart rate can be used to estimate rate of oxygen consumption in free-ranging king penguins even over a small time scale (30 min). However, (i) the type of activity of the bird must be known and (ii) the body condition of the bird must be accurately determined. More investigations on the impact of fasting and/or inactivity on this relationship are required to refine these estimates further.

Seasonal hypothermia in a large migrating bird: saving energy for fat deposition?

We have tested the hypothesis that a large (2 kg) migratory bird, such as the barnacle goose Branta leucopsis, becomes hypothermic before its autumn migration, when food is not scarce, but when it is necessary to conserve and/or store energy in the form of fat. Abdominal temperature (T(ab)) was measured in wild geese using an implanted data logger. Commencing a few days before and continuing until approximately 20 days after the start of their autumn migration, mean daily T(ab) fell progressively by 4.4 degrees C. Thus, it is suggested that, rather than increasing the rate of pre-migratory fattening, the energy saved as a result of this hypothermia reduces the rate at which fat is used and thus enables its more rapid replacement following and, possibly during, migration. The energy saved may also be used for the replacement of non-fat tissues such as the locomotory muscles and gastro-intestinal tract. These observations are the first of their kind from birds in their natural environment and, together with other data, demonstrate that hypothermia in endotherms is not necessarily related to extremely low environmental temperature, to shortage of food or to the resting phase of the daily cycle. The data also highlight the relationship between hypothermia and fat deposition over extended periods in relatively large, endothermic animals and may have some relevance to obesity in humans.

Heart rate and rate of oxygen consumption of exercising macaroni penguins.

Twenty-four macaroni penguins (Eudyptes chrysolophus) from three groups, breeding males (N=9), breeding females (N=9) and moulting females (N=6), were exercised on a variable-speed treadmill. Heart rate (fH) and mass-specific rate of oxygen consumption (sVO2) were recorded from the animals, and both fh and sVO2 were found to increase linearly with increasing treadmill speed. A linear regression equation described the relationship between fh and sVO2 for each individual. There were no significant differences in these regressions between breeding and moulting females. There were significant differences in these relationships between all females and breeding males. fH and s VO2 were recorded from five of these animals for a total of 24 h. When fh was used to predict sVO2 for the 24 h period using the derived regressions, the estimate was not significantly different from the measured values, with an average error of -2.1 %. When fh was used to predict sVO2 for the 5 min intervals used for the calibration in all 24 birds, the estimate was not significantly different from the observed values, and the average error was only +0.47 %. Since the fH/sVO2 relationship was the same during periods of the annual cycle when the animals were inactive/fasting and active/foraging, it seems reasonable that, as long as sex differences are taken into account, fh can be used to predict the metabolic rates of free-ranging macaroni penguins all year round.

Impact of externally attached loggers on the diving behaviour of the king penguin.

The impact of relatively small externally attached time series recorders on some foraging parameters of seabirds was investigated during the austral summer of 1995 by monitoring the diving behaviour of 10 free-ranging king penguins (Aptenodytes patagonicus) over one foraging trip. Time-depth recorders were implanted in the abdominal cavities of the birds, and half of the animals also had dummy loggers attached on their backs. Although most of the diving behaviour was not significantly affected by the external loggers (P>0.05), the birds with externally attached loggers performed almost twice as many shallow dives, between 0 and 10 m depth, as the birds without external loggers. These shallow dives interrupted more frequently the deep-diving sequences in the case of birds with external loggers (percentage of deep dives followed by deep dives: 46% for birds with implants only vs. 26% for birds with an external attachment). Finally, the distribution pattern of the postdive durations plotted against the hour of the day was more heterogeneous for the birds with an external package. In addition, these penguins had extended surfacing times between two deep dives compared to birds without external attachments (P<0.0001). These results suggest the existence of an extra energy cost induced by externally attached loggers.

Heart rate and rate of oxygen consumption during flight of the barnacle goose, Branta leucopsis.

We report the first measurements of heart rate (f(H)) and the rate of oxygen consumption (V(O(2))) during flights from a species of bird larger than 500 g. V(O(2))was obtained from nine forward flapping flights of 8.9 min mean duration at a mean speed of 13.2 m s(-1) performed by three barnacle geese of mean mass 1.68 kg. Mean V(O(2))was 332 ml min(-1)or 201 ml min(-1) kg(-1). Sixteen flights were obtained from two of these birds equipped with heart rate data loggers, both when they were wearing a V(O(2)) mask and when they were not. During flights with the mask (mean duration 7.4 min), mean f(H) was 472 beats per min and during flights without the mask (mean duration 8.0 min) it was 391 beats per min. Heart rate was also measured in another goose flying without a respiratory mask and mean f(H) for all the three birds (mean mass 1.7 kg) flying without a mask for an average of 7.9 min at 13 m s(-1) was 378 beats per min. Resting f(H) for these three birds was 79 beats per min. The values of f(H) during flight are greater than those obtained from the same species during their autumn migration from Spitsbergen to southern Scotland. The possible reasons for this are discussed.

Estimation of the rate of oxygen consumption of the common eider duck (Somateria mollissima), with some measurements of heart rate during voluntary dives.

The relationship between heart rate (f(H)) and rate of oxygen consumption (V(O2)) was established for a marine diving bird, the common eider duck (Somateria mollissima), during steady-state swimming and running exercise. Both variables increased exponentially with speed during swimming and in a linear fashion during running. Eleven linear regressions of V(O2) (ml kg(-1 )min(-1)) on f(H) (beats min(-1)) were obtained: five by swimming and six by running the birds. The common regression was described by V(O2)=10.1 + 0.15f(H) (r(2)=0.46, N=272, P<0.0001). The accuracy of this relationship for predicting mean V(O2) was determined for a group of six birds by recording f(H) continuously over a 2-day period and comparing estimated V(O2) obtained using the common regression with (i) V(O2) estimated using the doubly labelled water technique (DLW) and (ii) V(O2) measured using respirometry. A two-pool model produced the most accurate estimated V(O2) using DLW. Because of individual variability within mean values of V(O2) estimated using both techniques, there was no significant difference between mean V(O2) estimated using f(H) or DLW and measured V(O2) values (P>0.2), although individual errors were substantially less when f(H) was used rather than DLW to estimate V(O2). Both techniques are, however, only suitable for estimating mean V(O2) for a group of animals, not for individuals. Heart rate and behaviour were monitored during a bout of 63 voluntary dives by one female bird in an indoor tank 1.7 m deep. Tachycardia occurred both in anticipation of and following each dive. Heart rate decreased before submersion but was above resting values for the whole of the dive cycle. Mean f(H) at mean dive duration was significantly greater than f(H) while swimming at maximum sustainable surface speeds. Heart rate was used to estimate mean V(O2) during the dive cycle and to predict aerobic dive limit (ADL) for shallow dives.

Heart rate and behavior of fur seals: implications for measurement of field energetics.

Archival data loggers were used to collect information about depth, swimming speed, and heart rate in 23 free-ranging antarctic fur seals. Deployments averaged 9.6 +/- 5.6 days (SD) and totaled 191 days of recording. Heart rate averaged 108.7 +/- 17.7 beats/min (SD) but varied from 83 to 145 beats/min among animals. Morphometrics explained most variations in heart rate among animals. These interacted with diving activity and swimming speed to produce a complex relationship between heart rate and activity patterns. Heart rate was also correlated with behavior over time lags of several hours. There was significant (P < 0.05) variation among animals in the degree of diving bradycardia. On average, heart rate declined from 100-130 beats/min before the dive to 70-100 beats/min during submersion. On the basis of the relationship between heart rate and rate of oxygen consumption, the overall metabolic rate was 5.46 +/- 1.61 W/kg (SD). Energy expenditure appears to be allocated to different activities within the metabolic scope of individual animals. This highlights the possibility that some activities can be mutually exclusive of one another.

Body cooling and its energetic implications for feeding and diving of tufted ducks.

Wintering in a temperate climate with low water temperatures is energetically expensive for diving ducks. The energy costs associated with body cooling due to diving and ingesting large amounts of cold food were measured in tufted ducks (Aythya fuligula) feeding on zebra mussels (Dreissena polymorpha), using implanted heart rate and body temperature transmitters. The effects of diving depth and food ingestion were measured in two sets of experiments: we measured body cooling and energy costs of six tufted ducks diving to different depths in a 6-m-deep indoor tank; the costs for food ingestion and crushing mussel shells were assessed under seminatural winter conditions with the same ducks feeding on mussels in a 1.5-m-deep outdoor pond. Body temperature dropped during feeding bouts and increased gradually during intermittent resting periods. The temperature drop increased linearly with dive duration. The rate of body cooling increased with feeding depth, but it was lower again at depths below 4 m. Half of the increment in energy costs of diving can be attributed to thermoregulatory heat production, of which approximately 50% is generated after diving to warm up the body. The excess costs for ducks feeding on large-sized mussels could be entirely explained by the estimated energy cost necessary to compensate the heat loss following food ingestion, suggesting that the heat production from shell crushing substituted for thermoregulation. Recovery from heat loss is probably a major component of the activity budget of wintering diving ducks.