Energy expenditure for thermoregulation and locomotion in emperor penguins

Skeletal muscle metabolism in sea-acclimatized king penguins. I. Thermogenic mechanisms

At fledging, king penguin juveniles undergo a major energetic challenge to overcome the intense and prolonged energy demands for thermoregulation and locomotion imposed by life in cold seas. Among other responses, sea acclimatization triggers fuel selection in skeletal muscle metabolism towards lipid oxidation in vitro, which is reflected by a drastic increase in lipid-induced thermogenesis in vivo However, the exact nature of skeletal muscle thermogenic mechanisms (shivering and/or non-shivering thermogenesis) remains undefined. The aim of the present study was to determine in vivo whether the capacity for non-shivering thermogenesis was enhanced by sea acclimatization. We measured body temperature, metabolic rate, heart rate and shivering activity in fully immersed king penguins (Aptenodytes patagonicus) exposed to water temperatures ranging from 12 to 29°C. Results from terrestrial pre-fledging juveniles were compared with those from sea-acclimatized immature penguins (hereafter 'immatures'). The capacity for thermogenesis in water was as effective in juveniles as in immatures, while the capacity for non-shivering thermogenesis was not reinforced by sea acclimatization. This result suggests that king penguins mainly rely on skeletal muscle contraction (shivering or locomotor activity) to maintain endothermy at sea. Sea-acclimatized immature penguins also exhibited higher shivering efficiency and oxygen pulse (amount of oxygen consumed or energy expended per heartbeat) than pre-fledging juvenile birds. Such increase in shivering and cardiovascular efficiency may favor a more efficient activity-thermoregulatory heat substitution providing penguins with the aptitude to survive the tremendous energetic challenge imposed by marine life in cold circumpolar oceans.

The TRP Channels Pkd2, NompC, and Trpm Act in Cold-Sensing Neurons to Mediate Unique Aversive Behaviors to Noxious Cold in Drosophila

The basic mechanisms underlying noxious cold perception are not well understood. We developed Drosophila assays for noxious cold responses. Larvae respond to near-freezing temperatures via a mutually exclusive set of singular behaviors-in particular, a full-body contraction (CT). Class III (CIII) multidendritic sensory neurons are specifically activated by cold and optogenetic activation of these neurons elicits CT. Blocking synaptic transmission in CIII neurons inhibits CT. Genetically, the transient receptor potential (TRP) channels Trpm, NompC, and Polycystic kidney disease 2 (Pkd2) are expressed in CIII neurons, where each is required for CT. Misexpression of Pkd2 is sufficient to confer cold responsiveness. The optogenetic activation level of multimodal CIII neurons determines behavioral output, and visualization of neuronal activity supports this conclusion. Coactivation of cold- and heat-responsive sensory neurons suggests that the cold-evoked response circuitry is dominant. Our Drosophila model will enable a sophisticated molecular genetic dissection of cold nociceptive genes and circuits.

Energetics of communal roosting in chestnut-crowned babblers: implications for group dynamics and breeding phenology

For many endotherms, communal roosting saves energy in cold conditions, but how this might affect social dynamics or breeding phenology is not well understood. Using chestnut-crowned babblers (Pomatostomus ruficeps), we studied the effects of nest use and group size on roosting energy costs. These 50 g cooperatively breeding passerine birds of outback Australia breed from late winter to early summer and roost in huddles of up to 20 in single-chambered nests. We measured babbler metabolism at three ecologically relevant temperatures: 5°C (similar to minimum nighttime temperatures during early breeding), 15°C (similar to nighttime temperatures during late breeding) and 28°C (thermal neutrality). Nest use alone had modest effects: even for solitary babblers at 5°C, it reduced nighttime energy expenditures by <15%. However, group-size effects were substantial, with savings of up to 60% in large groups at low temperatures. Babblers roosting in groups of seven or more at 5°C, and five or more at 15°C, did not need to elevate metabolic rates above basal levels. Furthermore, even at 28°C (thermoneutral for solitary babblers), individuals in groups of four or more had 15% lower basal metabolic rate than single birds, hinting that roosting in small groups is stressful. We suggest that the substantial energy savings of communal roosting at low temperatures help explain why early breeding is initiated in large groups and why breeding females, which roost alone and consequently expend 120% more energy overnight than other group members, suffer relatively higher mortality than communally roosting group mates.

Fat King Penguins Are Less Steady on Their Feet

Returning to the shore after a feeding sojourn at sea, king penguins often undertake a relatively long terrestrial journey to the breeding colony carrying a heavy, mostly frontal, accumulation of fat along with food in the stomach for chick-provisioning. There they must survive a fasting period of up to a month in duration, during which their complete reliance on endogenous energy stores results in a dramatic loss in body mass. Our aim was to determine if the king penguin’s walking gait changes with variations in body mass. We investigated this by walking king penguins on a treadmill while instrumented with an acceleration data logger. The stride frequency, dynamic body acceleration (DBA) and posture of fat (pre-fasting; 13.2 kg) and slim (post fasting; 11 kg) king penguins were assessed while they walked at the same speed (1.4km/h) on a treadmill. Paired statistical tests indicated no evidence for a difference in dynamic body acceleration or stride frequency between the two body masses however there was substantially less variability in both leaning angle and the leaning amplitude of the body when the birds were slimmer. Furthermore, there was some evidence that the slimmer birds exhibited a decrease in waddling amplitude. We suggest the increase in variability of both leaning angle and amplitude, as well as a possibly greater variability in the waddling amplitude, is likely to result from the frontal fat accumulation when the birds are heavier, which may move the centre of mass anteriorly, resulting in a less stable upright posture. This study is the first to use accelerometry to better understand the gait of a species within a specific ecological context: the considerable body mass change exhibited by king penguins.

Effect of walking speed on the gait of king penguins: An accelerometric approach

Little is known about non-human bipedal gaits. This is probably due to the fact that most large animals are quadrupedal and that non-human bipedal animals are mostly birds, whose primary form of locomotion is flight. Very little research has been conducted on penguin pedestrian locomotion with the focus instead on their associated high energy expenditure. In animals, tri-axial accelerometers are frequently used to estimate physiological energy cost, as well as to define the behaviour pattern of a species, or the kinematics of swimming. In this study, we showed how an accelerometer-based technique could be used to determine the biomechanical characteristics of pedestrian locomotion. Eight king penguins, which represent the only family of birds to have an upright bipedal gait, were trained to walk on a treadmill. The trunk tri-axial accelerations were recorded while the bird was walking at four different speeds (1.0, 1.2, 1.4 and 1.6km/h), enabling the amplitude of dynamic body acceleration along the three axes (amplitude of DBAx, DBAy and DBAz), stride frequency, waddling and leaning amplitude, as well as the leaning angle to be defined. The magnitude of the measured variables showed a significant increase with increasing speed, apart from the backwards angle of lean, which decreased with increasing speed. The variability of the measured variables also showed a significant increase with speed apart from the DBAz amplitude, the waddling amplitude, and the leaning angle, where no significant effect of the walking speed was found. This paper is the first approach to describe 3D biomechanics with an accelerometer on wild animals, demonstrating the potential of this technique.

Huddling reduces evaporative water loss in torpid Natterer's bats, Myotis nattereri

Periodic arousals during hibernation consume most of the winter energy budget for hibernating mammals. Evaporative water loss (EWL) is thought to affect the frequency of arousals and thus energy balance, and might have dramatic implications for over-winter survival and fitness. We hypothesized that huddling affects EWL and energy expenditure in torpid mammals. We tested this hypothesis using bats as a model and predicted that, during torpor, EWL and energy expenditure of huddling individuals would be lower than in individuals that are not in a huddle. We measured EWL and metabolic rate of torpid Myotis nattereri (Kuhl, 1817) huddling in groups or roosting individually. Evaporative water loss in huddling individual bats was almost 30% lower than in solitary animals (P=0.03), even after correcting for the effects of metabolic rate. Our results suggest that conservation of water is a substantial benefit underlying huddling by bats during hibernation. Ultimately, huddling could reduce the total cost of hibernation by reducing the number of expensive periodic arousals from torpor caused by the need to supplement water.

Effect of dietary fatty acids on metabolic rate and nonshivering thermogenesis in golden hamsters

Hibernating rodents prior to winter tend to select food rich in polyunsaturated fatty acids (PUFA). Several studies found that such diet may positively affect their winter energy budget by enhancing torpor episodes. However, the effect of composition of dietary fatty acids (FA) on metabolism of normothermic heterotherms is poorly understood. Thus we tested whether diets different in FA composition affect metabolic rate (MR) and the capacity for nonshivering thermogenesis (NST) in normothermic golden hamsters (Mesocricetus auratus). Animals were housed in outdoor enclosures from May 2010 to April 2011 and fed a diet enriched with PUFA (i.e., standard food supplemented weekly with sunflower and flax seeds) or with saturated and monounsaturated fatty acids (SFA/MUFA, standard food supplemented with mealworms). Since diet rich in PUFA results in lower MR in hibernating animals, we predicted that PUFA-rich diet would have similar effect on MR of normothermic hamsters, that is, normothermic hamsters on the PUFA diet would have lower metabolic rate in cold and higher NST capacity than hamsters supplemented with SFA/MUFA. Indeed, in winter resting metabolic rate (RMR) below the lower critical temperature was higher and NST capacity was lower in SFA/MUFA-supplemented animals than in PUFA-supplemented ones. These results suggest that the increased capacity for NST in PUFA-supplemented hamsters enables them lower RMR below the lower critical temperature of the thermoneural zone.

Emperor penguin body surfaces cool below air temperature

Emperor penguins Aptenodytes forsteri are able to survive the harsh Antarctic climate because of specialized anatomical, physiological and behavioural adaptations for minimizing heat loss. Heat transfer theory predicts that metabolic heat loss in this species will mostly depend on radiative and convective cooling. To examine this, thermal imaging of emperor penguins was undertaken at the breeding colony of Pointe Géologie in Terre Adélie (66°40' S 140° 01' E), Antarctica in June 2008. During clear sky conditions, most outer surfaces of the body were colder than surrounding sub-zero air owing to radiative cooling. In these conditions, the feather surface will paradoxically gain heat by convection from surrounding air. However, owing to the low thermal conductivity of plumage any heat transfer to the skin surface will be negligible. Future thermal imaging studies are likely to yield further insights into the adaptations of this species to the Antarctic climate.

The relationship between cutaneous water loss and thermoregulatory state in Kuhl's pipistrelle Pipistrellus kuhlii, a Vespertillionid bat

Total evaporative water loss is the sum of respiratory water loss (RWL) and cutaneous water loss (CWL) and constitutes the main avenue of water loss in bats. Because bats fly and have large surface-to-volume ratios, they potentially have high rates of RWL and CWL. Most species of small insectivorous bats have the ability to reduce their body temperature (T(b)) at rest, which substantially reduces energy expenditure and water loss. We hypothesized that bats reduce evaporative water loss during bouts of deep hypothermia (torpor) by decreasing RWL and CWL. We measured T(b), RWL, CWL, and resting metabolic rate (RMR) in Kuhl's pipistrelle Pipistrellus kuhlii, a small insectivorous bat. In support of our hypothesis, we found that RWL decreased with decreasing RMR. We found that CWL was lower in torpid individuals than in normothermic bats; however, bats in deep torpor had similar or higher CWL than bats in shallow torpor, suggesting that they exert a less effective physiological control over CWL when in deep torpor. Because insectivorous bats spend most of their lives in torpor or hibernation, the regulation of CWL in different heterothermic states has relevant ecological and evolutionary consequences.

Diet affects resting, but not basal metabolic rate of normothermic Siberian hamsters acclimated to winter

We examined the effect of different dietary supplements on seasonal changes in body mass (m(b)), metabolic rate (MR) and nonshivering thermogenesis (NST) capacity in normothermic Siberian hamsters housed under semi-natural conditions. Once a week standard hamster food was supplemented with either sunflower and flax seeds, rich in polyunsaturated fatty acids (FA), or mealworms, rich in saturated and monounsaturated FA. We found that neither of these dietary supplements affected the hamsters' normal winter decrease in m(b) and fat content nor their basal MR or NST capacity. NST capacity of summer-acclimated hamsters was lower than that of winter-acclimated ones. The composition of total body fat reflected the fat composition of the dietary supplements. Resting MR below the lower critical temperature of the hamsters, and their total serum cholesterol concentration were lower in hamsters fed a diet supplemented with mealworms than in hamsters fed a diet supplemented with seeds. These results indicate that in mealworm-fed hamsters energy expenditure in the cold is lower than in animals eating a seed-supplemented diet, and that the degree of FA unsaturation of diet affects energetics of heterotherms, not only during torpor, but also during normothermy.

Heterothermy, and the energetic consequences of huddling in small migrating passerine birds

The success of migration of small passerine birds depends largely on effective refueling at stopover sites. In our previous studies, we found that hypothermia facilitates accumulation of fuel at the beginning of a stopover. Later we found that blackcaps, Sylvia atricapilla, might further reduce their energy expenditure by huddling while at rest. Here, we report experimental results supporting our hypothesis that huddling is beneficial to small migrating passerines both from energetic and thermoregulatory points of view. To test this hypothesis we measured metabolic rates and body temperatures of seven blackcaps placed in respirometry chambers overnight, either solitarily or in groups of three or four at ambient temperatures of 5, 10, and 15°C. Concurring with our predictions, huddling blackcaps maintained higher body temperatures than did solitary birds, but had mass-specific metabolic rates lower by ∼30% than those of solitary individuals. Based on our previous studies, we estimated energy savings through huddling to be comparable to energy savings through hypothermia in solitary blackcaps and suggest that huddling may be an important way of saving energy for small passerine birds resting at migratory stopovers. At the same time it might offer the additional benefit of lower risk of predation. In this light, we predict that huddling occurs frequently in nature, leading to significant savings of energy, faster accumulation of fuel, presumably lower risk of becoming a prey, more successful migration, and eventually increased fitness.

What triggers the aerobic dive limit? Patterns of muscle oxygen depletion during dives of emperor penguins

The physiological basis of the aerobic dive limit (ADL), the dive duration associated with the onset of post-dive blood lactate elevation, is hypothesized to be depletion of the muscle oxygen (O(2)) store. A dual wavelength near-infrared spectrophotometer was developed and used to measure myoglobin (Mb) O(2) saturation levels in the locomotory muscle during dives of emperor penguins (Aptenodytes forsteri). Two distinct patterns of muscle O(2) depletion were observed. Type A dives had a monotonic decline, and, in dives near the ADL, the muscle O(2) store was almost completely depleted. This pattern of Mb desaturation was consistent with lack of muscle blood flow and supports the hypothesis that the onset of post-dive blood lactate accumulation is secondary to muscle O(2) depletion during dives. The mean type A Mb desaturation rate allowed for calculation of a mean muscle O(2) consumption of 12.4 ml O(2) kg(-1) muscle min(-1), based on a Mb concentration of 6.4 g 100 g(-1) muscle. Type B desaturation patterns demonstrated a more gradual decline, often reaching a mid-dive plateau in Mb desaturation. This mid-dive plateau suggests maintenance of some muscle perfusion during these dives. At the end of type B dives, Mb desaturation rate increased and, in dives beyond the ADL, Mb saturation often reached near 0%. Thus, although different physiological strategies may be used during emperor penguin diving, both Mb desaturation patterns support the hypothesis that the onset of post-dive lactate accumulation is secondary to muscle O(2) store depletion.

The use of body mass loss to estimate metabolic rate in birds

During starvation, energy production occurs at the expense of body reserve utilisation which results in body mass loss. Knowing the role of the fuels involved in this body mass loss, along with their energy density, can allow an energy equivalent of mass loss to be calculated. Therefore, it is possible to determine daily energy expenditure (DEE) if two body mass loss measurements at an interval of a few days are obtained. The technique can be cheap, minimally stressful for the animals involved, and the data relatively simple to gather. Here we review the use of body mass loss to estimate DEE in birds through critiquing the strengths and weaknesses of the technique, and detail the methodology and considerations that must be adhered to for accurate measures of DEE to be obtained. Owing to the biology of the species, the use of the technique has been used predominantly in Antarctic seabirds, particularly penguins and albatrosses. We demonstrate how reliable the technique can be in predicting DEE in a non-Antarctic species, common eiders (Somateria mollissima), the female of which undergoes a fasting period during incubation. We conclude that using daily body mass loss to estimate DEE can be a useful and effective approach provided that (1) the substrate being consumed during mass loss is known, (2) the kinetics of body mass loss are understood for the species in question and (3) only species that enter a full phase II of a fast (where substrate catabolism reaches a steady state) and are not feeding for a period of time are appropriate for this method.

Flight modes in migrating European bee-eaters: heart rate may indicate low metabolic rate during soaring and gliding

Background

Many avian species soar and glide over land. Evidence from large birds (m_b>0.9 kg) suggests that soaring-gliding is considerably cheaper in terms of energy than flapping flight, and costs about two to three times the basal metabolic rate (BMR). Yet, soaring-gliding is considered unfavorable for small birds because migration speed in small birds during soaring-gliding is believed to be lower than that of flapping flight. Nevertheless, several small bird species routinely soar and glide.

Methodology/Principal Findings

To estimate the energetic cost of soaring-gliding flight in small birds, we measured heart beat frequencies of free-ranging migrating European bee-eaters (Merops apiaster, m_b∼55 g) using radio telemetry, and established the relationship between heart beat frequency and metabolic rate (by indirect calorimetry) in the laboratory. Heart beat frequency during sustained soaring-gliding was 2.2 to 2.5 times lower than during flapping flight, but similar to, and not significantly different from, that measured in resting birds. We estimated that soaring-gliding metabolic rate of European bee-eaters is about twice their basal metabolic rate (BMR), which is similar to the value estimated in the black-browed albatross Thalassarche (previously Diomedea) melanophrys, m_b∼4 kg). We found that soaring-gliding migration speed is not significantly different from flapping migration speed.

Conclusions/Significance

We found no evidence that soaring-gliding speed is slower than flapping flight in bee-eaters, contradicting earlier estimates that implied a migration speed penalty for using soaring-gliding rather than flapping flight. Moreover, we suggest that small birds soar and glide during migration, breeding, dispersal, and other stages in their annual cycle because it may entail a low energy cost of transport. We propose that the energy cost of soaring-gliding may be proportional to BMR regardless of bird size, as theoretically deduced by earlier studies.

One for all and all for one: the energetic benefits of huddling in endotherms

Huddling can be defined as "an active and close aggregation of animals". It is a cooperative group behaviour, permitting individuals involved in social thermoregulation to minimize heat loss and thereby lower their energy expenditure, and possibly allowing them to reallocate the saved energy to other functions such as growth or reproduction. Huddling is especially important in the case of animals faced with high heat loss due to a high surface-to-volume ratio, poor insulation, or living in cold environments. Although numerous experimental studies have focused on the huddling behaviour of a wide range of species, to our knowledge, this is the first attempt to review the various implications of this widely used behavioural strategy. Huddling allows individuals to maximise energy savings by (1) decreasing their cold-exposed body surface area, (2) reducing their heat loss through warming of ambient temperatures surrounding the group, and (3) eventually lowering their body temperature through physiological processes. Huddling provides substantial energy savings and is estimated to reduce energy expenditure by between 6 and 53%. Broad variations in the energetic benefits of huddling depend on the number of individuals and species involved in huddles, the ambient temperatures to which individuals are exposed and the density of the aggregations. It has been shown that huddling individuals have increased survival, a lower food intake, a decreased body mass loss, increased growth rate, reduced water loss, and/or a more constant body temperature together with a significant reduction in metabolic rate. Though huddling has been studied widely, this review reveals the intricacies of this adaptive behaviour.

Heterothermy in small, migrating passerine birds during stopover: use of hypothermia at rest accelerates fuel accumulation

For small endothermic animals, heterothermy serves as an energy-saving mechanism for survival in challenging environments, but it may also accelerate fat accumulation in individuals preparing for fuel-demanding activities. This is the first study to demonstrate adaptive hypothermic responses in migrating passerines. While monitoring body temperature (Tb) of eight blackcaps (Sylvia atricapilla) by radiotelemetry, we found that during daytime Tb=42.5±0.4°C (mean ±s.d.); at night Tb decreased to a minimum between 33 and 40°C. We determined the lower limit for normothermy at 37.4°C and found that on 12 out of 34 bird-nights of observations under semi-natural conditions blackcaps reduced their Tb below normothermic resting levels with minimum values of 33 and 34.5°C compared with rest-phase normothermic Tb of 38.8±0.8°C. In birds of body mass (mb) <16.3 g, minimum Tb at night correlated with the individual's mb (r=0.67, P<0.01, N=17),but this was not the case in birds with mb>16.3 g. Minimum nocturnal Tb did not correlate with night-time air temperature (Ta). Measurements of metabolic rate in birds subjected to a Ta of 15°C showed that hypothermia of this magnitude can lead to a reduction of some 30% in energy expenditure compared with birds remaining normothermic. Our data suggest that by reducing the Tb–Ta gradient, blackcaps accelerate their rate of fuel accumulation at a stopover. When body energy reserves are low blackcaps may achieve this reduction by entering hypothermia. Since hypothermia, as seen in blackcaps, may lead to significant energy savings and facilitate body mass gain, we predict that it is common among small migrating passerines.

Emperor penguin mates: keeping together in the crowd

As emperor penguins have no breeding territories, a key issue for both members of a pair is not to be separated until the egg is laid and transferred to the male. Both birds remain silent after mating and thereby reduce the risk of having the pair bond broken by unpaired birds. However, silence prevents finding each other if the pair is separated. Huddles-the key to saving energy in the cold and the long breeding fast-continuously form and break up, but not all birds are involved simultaneously. We studied the behaviour of four pairs before laying. Temperature and light intensity measurements allowed us to precisely detect the occurrence of huddling episodes and to determine the surrounding temperature. The four pairs huddled simultaneously for only 6 per cent of the time when weather conditions were harshest. Despite this asynchrony, the huddling behaviour and the resulting benefits were similar between pairs. By contrast, the huddling behaviour of mates was synchronized for 84 per cent of events. By coordinating their huddling behaviour during courtship despite the apparent confusion within a huddle and its ever-changing structure, both individuals save energy while securing their partnership.

Energy saving processes in huddling emperor penguins: from experiments to theory

This paper investigates the energy savings of male emperor penguins Aptenodytes forsteri linked to their huddling behaviour, the key factor that allows them to assume their incubating task while undergoing a long fast. Drawing on new studies by our team, this review examines the energetic benefits accrued from huddling and estimates the respective contributions of wind protection, exposure to mild ambient temperatures, reduction in cold-exposed body surfaces and body temperature adjustments in these energy savings. The metabolic rate of 'loosely grouped' birds (restrained in small groups of 5-10 individuals, which are unable to huddle effectively) is reduced by 39% compared to metabolic rate of 'isolated' birds, with 32% of these energetic benefits due to wind protection. In addition, metabolic rate of 'free-ranging' emperors, i.e. able to move freely and to huddle, is on average 21% lower than that of 'loosely grouped' birds. Exposure to mild ambient temperatures within the groups and reduction in cold-exposed body surfaces while huddling, though overestimated, would represent a 38% metabolic reduction. About two thirds of metabolic lowering is attributable to the reduction in cold-exposed body surfaces and one third to the mild microclimate created within the groups. Moreover, body temperature adjustments contribute to these energetic benefits: maintaining body temperatures 1 degrees C lower would represent a 7-17% reduction in energy expenditure. These processes, linked together, explain how huddling emperors save energy and maintain a constant body temperature, which ensures a successful incubation in the midst of the austral winter.

The penguin waddling gait pattern has a more consistent step width than step length

Previous research has indicated that the sagittal plane gait dynamics of humans are more stable and less dependent on active neural control, while the frontal plane dynamics are less stable and require greater neural control. The higher neural demands of the frontal plane dynamics are reflected in a more variable step width than step length. Greater variability in the step width occurs because humans modulate their foot placement for each step to ensure stability and prevent falls. Compared to other terrestrial animals, penguins appear to have excessive amount of frontal plane motion in their gait that is characterized as waddling. If excessive frontal plane motion requires additional neural control and is associated with falls, it would seem that evolutionary pressures would have eliminated such locomotive strategies. Here we measured the step length and width variability to determine if waddling results in a less stable gait. Remarkably, the variability of the step width was less than the variability of the step length. These results are directly opposite of what has been reported for humans. Hence, our data indicate that waddling may be an effective strategy for ensuring stability in the frontal plane dynamics.

Onshore energetics in penguins: Theory, estimation and ecological implications

Penguins are known to have high pedestrian locomotory costs in comparison to other cursorial birds, but the ecological consequences of this difference have received limited attention. Here we present a method for the accurate estimation of onshore energetics based on measurements of body mass, simple morphometrics and distance moved. The method is shown to be similarly accurate to other field-based estimates of energy expenditure, but has the advantage of logistical simplicity. King penguins spend 30-50% of their time ashore and may walk distances of several kilometres to and from their breeding colonies. However, in such cases the total energetic cost of pedestrian locomotion is estimated to be only 1.0% of the energy expended whilst ashore. Thus, despite a high instantaneous cost, pedestrian locomotion is a small and possibly negligible component of total energy turnover in king penguins.

Body temperature changes induced by huddling in breeding male emperor penguins

Huddling is the key energy-saving mechanism for emperor penguins to endure their 4-mo incubation fast during the Antarctic winter, but the underlying physiological mechanisms of this energy saving have remained elusive. The question is whether their deep body (core) temperature may drop in association with energy sparing, taking into account that successful egg incubation requires a temperature of about 36°C and that ambient temperatures of up to 37.5°C may be reached within tight huddles. Using data loggers implanted into five unrestrained breeding males, we present here the first data on body temperature changes throughout the breeding cycle of emperor penguins, with particular emphasis on huddling bouts. During the pairing period, core temperature decreased progressively from 37.5 ± 0.4°C to 36.5 ± 0.3°C, associated with a significant temperature drop of 0.5 ± 0.3°C during huddling. In case of egg loss, body temperature continued to decrease to 35.5 ± 0.4°C, with a further 0.9°C decrease during huddling. By contrast, a constant core temperature of 36.9 ± 0.2°C was maintained during successful incubation, even during huddling, suggesting a trade-off between the demands for successful egg incubation and energy saving. However, such a limited drop in body temperature cannot explain the observed energy savings of breeding emperor penguins. Furthermore, we never observed any signs of hyperthermia in huddling birds that were exposed to ambient temperatures as high as above 35°C. We suggest that the energy savings of huddling birds is due to a metabolic depression, the extent of which depends on a reduction of body surface areas exposed to cold.

Energy metabolism and evaporative water loss in the European free-tailed bat and Hemprich's long-eared bat (Microchiroptera): species sympatric in the Negev Desert

We compared the thermoregulatory abilities of two insectivorous bat species, Tadarida teniotis (mean body mass 32 g) and Otonycteris hemprichii (mean body mass 25 g), that are of different phylogenetic origins and zoogeographic distributions but are sympatric in the Negev Desert. At night, both were normothermic. By day, both were torpid when exposed to ambient temperatures (T(a)) below 25 degrees Celsius, with concomitant adjustments in metabolic rate (MR). Otonycteris hemprichii entered torpor at higher T(a) than T. teniotis, and, when torpid, their body temperatures (T(b)) were 1 degrees -2 degrees Celsius and 5 degrees -8 degrees Celsius above T(a), respectively; MR was correspondingly reduced. At night, the lower critical temperature of T. teniotis was 31.5 degrees Celsius, and that of O. hemprichii was 33 degrees Celsius. Mean nocturnal thermoneutral MR of T. teniotis was 37% greater than that of O. hemprichii. At high T(a), evaporative water loss (EWL) increased markedly in both species, but it was significantly higher in T. teniotis above 38 degrees Celsius. In both species, the dry heat transfer coefficient (thermal conductance) followed the expected pattern for small mammals, by day and by night. Total EWL was notably low in normothermic and torpid animals of both species, much lower than values reported for other bats, indicating efficient water conservation mechanisms in the study species. Comparing thermoregulatory abilities suggests that O. hemprichii is better adapted to hot, arid environments than T. teniotis, which may explain its wider desert distribution. By both standard and phylogenetically informed ANCOVA, we found no differences in basal metabolic rate (BMR) between desert and nondesert species of insectivorous bats, substantiating previous studies suggesting that low BMR is a characteristic common to insectivorous bats in general.

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.

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

We measured oxygen consumption rate (V̇o2) and body temperatures in 10 king penguins in air and water. V̇o2was 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 (Mb) was 13.8 ± 1.2 kg in fed and 11.0 ± 0.6 kg in fasted birds. After fasting, resting V̇o2was 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 V̇o2between air and water in fed animals (air: 117.1 ± 20.0 ml O2/min; water: 114.8 ± 32.7 ml O2/min, P > 0.6). In air, V̇o2decreased with Mb, while it increased with Mbin 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.

Cardiovascular adjustments during locomotion in penguins

The high costs of airborne flapping flight are reflected in a difference between the oxygen pulse (OP; amount of oxygen consumed per heart beat) during flight and that during terrestrial locomotion, as well as a difference in the relationship between heart rate (fH) and rate of oxygen consumption ([Formula: see text]O2). We tested and failed to accept the hypothesis that there would be similar differences in the fH–[Formula: see text]O2and [Formula: see text]O2–OP relationships during swimming under water and during walking for macaroni penguins (Eudyptes chrysolophus (Brandt, 1837)). We suggest that this may be a result of the penguins having to overcome physical forces different from those experienced by volant birds and possibly a response to limited access to oxygen while porpoising or diving. This result has important implications for those who wish to use fHto estimate [Formula: see text]O2and hence metabolic rate in the field for this and similar species. To test the utility of the relationship, we compared our results with data obtained previously for this species, and we simultaneously measured [Formula: see text]O2in a respirometer and estimated [Formula: see text]O2from fHfor 48 h. There was no significant difference in the fH–[Formula: see text]O2or [Formula: see text]O2–OP relationships between the two studies or between [Formula: see text]O2estimated from fHand that measured using respirometry.

The Allometry of Avian Basal Metabolic Rate: Good Predictions Need Good Data

Basal metabolic rate (BMR) is often predicted by allometric interpolation, but such predictions are critically dependent on the quality of the data used to derive allometric equations relating BMR to body mass (Mb). An examination of the metabolic rates used to produce conventional and phylogenetically independent allometries for avian BMR in a recent analysis revealed that only 67 of 248 data unambiguously met the criteria for BMR and had sample sizes with n>/=3. The metabolic rates that represented BMR were significantly lower than those that did not meet the criteria for BMR or were measured under unspecified conditions. Moreover, our conventional allometric estimates of BMR (W; logBMR=-1.461+0.669logMb) using a more constrained data set that met the conditions that define BMR and had n>/=3 were 10%-12% lower than those obtained in the earlier analysis. The inclusion of data that do not represent BMR results in the overestimation of predicted BMR and can potentially lead to incorrect conclusions concerning metabolic adaptation. Our analyses using a data set that included only BMR with n>/=3 were consistent with the conclusion that BMR does not differ between passerine and nonpasserine birds after taking phylogeny into account. With an increased focus on data mining and synthetic analyses, our study suggests that a thorough knowledge of how data sets are generated and the underlying constraints on their interpretation is a necessary prerequisite for such exercises.

Energetic cost of foraging in free-diving emperor penguins

Hypothesizing that emperor penguins (Aptenodytes forsteri) would have higher daily energy expenditures when foraging for their food than when being hand-fed and that the increased expenditure could represent their foraging cost, we measured field metabolic rates (FMR; using doubly labeled water) over 4-d periods when 10 penguins either foraged under sea ice or were not allowed to dive but were fed fish by hand. Surprisingly, penguins did not have higher rates of energy expenditure when they dove and captured their own food than when they did not forage but were given food. Analysis of time-activity and energy budgets indicated that FMR was about 1.7 x BMR (basal metabolic rate) during the 12 h d(-1) that penguins were lying on sea ice. During the remaining 12 h d(-1), which we termed their "foraging period" of the day, the birds were alert and active (standing, preening, walking, and either free diving or being hand-fed), and their FMR was about 4.1 x BMR. This is the lowest cost of foraging estimated to date among the eight penguin species studied. The calculated aerobic diving limit (ADL(C)), determined with the foraging period metabolic rate of 4.1 x BMR and known O(2) stores, was only 2.6 min, which is far less than the 6-min ADL previously measured with postdive lactate analyses in emperors diving under similar conditions. This indicates that calculating ADL(C) from an at-sea or foraging-period metabolic rate in penguins is not appropriate. The relatively low foraging cost for emperor penguins contributes to their relatively low total daily FMR (2.9 x BMR). The allometric relationship for FMR in eight penguin species, including the smallest and largest living representatives, is kJ d(-1)=1,185 kg(0.705).

Temperature regulation in emperor penguins foraging under sea ice

Inferior vena caval (IVC) and anterior abdominal (AA) temperatures were recorded in seven emperor penguins (Aptenodytes forsteri) foraging under sea ice in order to evaluate the hypothesis that hypothermia-induced metabolic suppression might extend aerobic diving time. Diving durations ranged from 1 to 12.5 min, with 39% of dives greater than the measured aerobic dive limit of 5.6 min. Anterior abdominal temperature decreased progressively throughout dives, and partially returned to pre-dive values during surface intervals. The lowest AA temperature was 19 degrees C. However, mean AA temperatures during dives did not correlate with diving durations. In six of seven penguins, only minor fluctuations in IVC temperatures occurred during diving. These changes were often elevations in temperature. In the one exception, although IVC temperatures decreased, the reductions were less than those in the anterior abdomen and did not correlate with diving durations. Because of these findings, we consider it unlikely that regional hypothermia in emperor penguins leads to a significant reduction in oxygen consumption of the major organs within the abdominal core. Rather, temperature profiles during dives are consistent with a model of regional heterothermy with conservation of core temperature, peripheral vasoconstriction, and cooling of an outer body shell.

Weather, microclimate, and energy costs of thermoregulation for breeding Adélie Penguins

We measured meteorological conditions and estimated the energy costs of thermoregulation for young and adult Adélie Penguins (Pygoscelis adeliae) at a breeding colony near the Antarctic Peninsula. Air temperatures averaged < 5°C and strong winds were frequent. Operative temperatures (T_e) for adults ranged from -8 to 28°C, averaging 5-6°C, for the period from courtship to fledging of chicks. The average energy cost of thermoregulation (C_th) for adult penguins was equivalent to 10-16% of basal metabolism. C_th comprised about 15% of the estimated daily energy budget (DEB) of incubating adults, but only about 1% of the DEB of adults feeding chicks. The T_e's for chicks older than 14 days ranged from 0 to 31°C, averaging 8.0 C. The C_th for downy chicks ranged from about 31% of minimal metabolic rate (MMR) in 1 kg chicks to about 10% of MMR in 3 kg chicks. Between initial thermal independence (age 12-14 days) and the cessation of parental feeding (age 35-40 days), chicks use about 10-11% of assimilated energy for thermoregulation. C_th is equivalent to about 17% of the MMR of fledglings during their 2-3 week fast. We observed no indication of thermal stress (i.e., conditions in which birds cannot maintain stable T_b) in adults and no indication of cold stress in any age class. However, on clear, calm days when air temperature exceeds 7-10°C for several hours, downy chicks are vulnerable to lethal hyperthermia.

Thermoregulation, gas exchange, and ventilation in Adelie penguins (Pygoscelis adeliae)

Adelie penguins (Pygoscelis adeliae) experience a wide range of ambient temperatures (Ta) in their natural habitat. We examined body temperature (Tb), oxygen consumption (VO2), carbon dioxide production (VCO2), evaporative water loss (mH2O), and ventilation at Ta from -20 to 30 degrees C. Body temperature did not change significantly between -20 and 20 degrees C (mean Tb = 39.3 degrees C). Tb increased slightly to 40.1 degrees C at Ta = 30 degrees C. Both VO2 and VCO2 were constant and minimal at Ta between -10 and 20 degrees C, with only minor increases at -20 and 30 degrees C. The minimal VO2 of adult penguins (mean mass 4.007 kg) was 0.0112 ml/[g.min], equivalent to a metabolic heat production (MHP) of 14.9 Watt. The respiratory exchange ratio was approximately 0.7 at all Ta. Values of mH2O were low at low Ta, but increased to 0.21 g/min at 30 degrees C, equivalent to 0.3% of body mass/h. Dry conductance increased 3.5-fold between -20 and 30 degrees C. Evaporative heat loss (EHL) comprised about 5% of MHP at low Ta, rising to 47% of MHP at Ta = 30 degrees C. The means of ventilation parameters (tidal volume [VT], respiration frequency [f], minute volume [VI], and oxygen extraction [EO2]) were fairly stable between -20 and 10 degrees C (VT did not change significantly over the entire Ta range). However, there was considerable inter- and intra-individual variation in ventilation patterns. At Ta = 20-30 degrees C, f increased 7-fold over the minimal value of 7.6 breaths/min, and VI showed a similar change.(ABSTRACT TRUNCATED AT 250 WORDS)

Food habits and the basal rate of metabolism in birds

The correlation of basal rate of metabolism with various factors is examined in birds. Chief among these is body mass. As in mammals, much of the remaining variation in basal rate among birds is associated with food habits. Birds other than passerines that feed on grass, nectar, flying insects, or vertebrates generally have basal rates that are similar to mammals of the same mass and food habits. In contrast, most invertebrate-eating birds that weigh over 100 g have higher basal rates than equally-sized, invertebrate-eating mammals. The high basal rates of small passerines equal those of small mammals that do not enter torpor and represent the minimal cost of continuous endothermy. Large passerines and small procellariiforms, charadriiforms, and psittaciforms generally have higher basal rates than mammals with the same mass and food habits. The high basal rates of passerines (in combination with altricial habits) may have significance in permitting high post-natal growth rates and the exploitation of seasonally abundant resources. These interrelations may contribute to the predominance of passerines in temperate land environments.

Ontogeny of thermoregulation and energy metabolism in pygoscelid penguin chicks

The ontogeny of thermoregulation and energy metabolism of chinstrap (Pygoscelis antarctica) and gentoo (P. papua) penguins was studied on King George Island, South Shetland Island, Antarctica. The major findings of this study are: Chinstrap and gentoo penguin chicks hatched completely poikilothermic, due to their poor heat-production ability at low ambient temperatures. They were able to maintain high body temperatures and metabolic rates only by being brooded by adults. Newly hatched chinstrap penguin chicks had, at a specified ambient temperature, significantly higher metabolic rates than newly hatched gentoos. Moreover, chinstrap chicks maintained a significantly higher body temperature. It is suggested that this is a non-acclimatory metabolic adaptation of chinstrap penguin chicks to the lower mean temperatures of their breeding areas. On the 15th day after hatching, chinstrap chicks were completely, and gentoo chicks almost completely, homeothermic. In spite of their high thermogenic capacity from about day 10, chicks were not at that time capable of controlling heat dissipation, and were still dependent on their parents. In older downy chicks and fledglings, heat loss at low temperatures, expressed as heat conductance (CA), was similar to that found for the adults of other penguin species. Just before moulting the CA of chicks was lower than after moulting. Moulting alone did not cause a clear increase in CA. Towards the end of their stay on land the CA of pre-fledged gentoos decreased by 31%. This decrease was not connected with the development of feathers or growth in the chicks' weight. The combination of the low CA and high SMR of chicks gave very low lower critical temperatures, near -15 degrees C. The wide thermoneutral zones of the chicks covered the whole range of air temperature variations in the breeding colonies of both species studied on King George Island. The CA values of homeothermic chinstrap chicks were not lower than those of gentoos, despite the more southern breeding range of the former species. The older chicks of both species are well protected against cold. Any further increase in insulation in chinstrap chicks would be of no adaptative importance.