Temperature regulation in the echidna (Tachyglossus aculeatus)

The echidna (Tachyglossus aculeatus) maintained a body temperature of 30.7°C ± 1.03 s.d. (N = 23) at ambient temperatures (T_A) between 0 and 25°C. It may, however, also become hypothermic at low T_A. At T_A = 30°C or above the echidna became hyperthermic. The thermoneutral range was about 20–30°C. At low T_A the metabolic rate might be increased several fold. The thermal conductance was at a minimum at T_A = 20°C, and was not further reduced at lower T_A. At higher T_A the thermal conductance increased up to five-fold. The evaporation showed little change with increasing T_A. At the highest T_A we used (33°C) the evaporation on the average accounted for the dissipation of only about one-third of the metabolic heat produced. These findings suggest that the echidna, although it can maintain its body temperature at low ambient temperature, cannot rely upon evaporation as the major avenue for heat loss at high ambient temperature.     

Thermoregulation in a large bird,the emu (Dromaius novaehollandiae)

The emu is a large, flightless bird native to Australia. Its habitats range from the high snow country to the arid interior of the continent. Our experiments show that the emu maintains a constant body temperature within the ambient temperature range-5 to 45°C. The males regulate their body temperature about 0.5°C lower than the females. With falling ambient temperature the emu regulates its body temperature initially by reducing conductance and then by increasing heat production. At-5°C the cost of maintaining thermal balance is 2.6 times basal metabolic rate. By sitting down and reducing heat loss from the legs the cost of homeothermy at-5°C is reduced to 1.5 times basal metabolic rate. At high ambient temperatures the emu utilises cutaneous evaporative water loss in addition to panting. At 45°C evaporation is equal to 160% of heat production. Panting accounts for 70% of total evaporation at 45°C. The cost of utilising cutaneous evaporation for the other 30% appears to be an increase in dry conductance.Abbreviations A _r Effective radiating surface area - BMR basal metabolic rate - C _dry dry conductance - CEWL cutaneous evaporative water loss - EHL evaporative heat loss - EWL evaporative water loss - FECO₂ fractional concentration of CO₂ in excurrent air - FF_H2O water content of chamber excurrent air - FEO₂ fractional concentration of O₂ in chamber excurrent air - FICO₂ fractional concentration of CO₂ in incurrent air - FIO₂ fractional concentration of O₂ in chamber incurrent air - MHP metabolic heat production - MR metabolic rate - REWL respiratory evaporative water loss - RH relative humidity - RQ respiratory quotient ; - SA surface area - SEM standard error of the mean - SNK Student-Newman-Keuls multiple range test - STPD standard temperature and pressure dry - T _a ambient temperature(s) - T _b body temperature(s) - T _e surface temperature(s) - flow rate of air into the chamber - carbon dioxide production - oxygen consumption - vapour pressure of water     

Rate of metabolism, temperature regulations, and evaporative water loss in the lesser gymnure Hylomys suillus (Insectivora, Mammalia)

Rate of metabolism, body temperature, wet thermal conductance, and evaporative water loss were measured at different ambient temperatures in four lesser gymnures Hylomys suillus. Gymnures responded as typical endothermic homoiotherms to changes in ambient temperature. Below the lower critical temperature of 32°C, they maintained a body temperature of 37.3± 0.3°C by an increased rate of metabolism. Minimum wet thermal conductance was 111% of that expected on the basis of body mass. Average basal rate of metabolism was 1.04 ml O₂ g⁻¹ h⁻¹, which represents 106% of the expected value. Within and above the thermoneutral zone, heat loss by evaporation did not account for more than 30% of the heat produced. As a consequence, the body temperature of gymnures was maintained 4°C above ambient temperature. These metabolic and thermoregulatory patterns differ strikingly from those of other members of the family Erinaceidac and can be interpreted as a result of physiological adaptation to a different ecology. Being smaller than hedgehogs and inhabiting montane tropical rainforests, lesser gymnures lack the physiological traits which enable many hedgehogs to invade hot, arid and/or strongly seasonal environments.     

Temperature regulation and metabolism of an Australian bat, Chalinolobus gouldii (Chiroptera: Vespertilionidae) when euthermic and torpid

The thermal and metabolic physiology of Chalinolobus gouldii, an Australian vespertilionid bat, was studied in the laboratory using flow-through respirometry. Chalinolobus gouldii exhibits a clear pattern of euthermic thermoregulation, typical of endotherms with respect to body temperature and rate of oxygen consumption. The basal metabolic rate of euthermic Chalinolobus gouldii is approximately 86% of that predicted for a 17.5-g mammal and falls into the range of mass-specific basal metabolic rates ascribed to vespertilionid bats. However, like most vespertilionid bats, Chalinolobus gouldii displays extreme thermolability. It is able to enter into torpor and spontaneously arouse at ambient temperatures as low as 5 °C. Torpid bats thermoconform at moderate ambient temperature, with body temperature ≈ ambient temperature, and have a low rate of oxygen consumption determined primarily by Q ₁₀ effects. At low ambient temperature (< 10 °C), torpid C. gouldii begin to regulate their body temperature by increased metabolic heat production; they tend to maintain a higher body temperature at low ambient temperature than do many northern hemisphere hibernating bats. Use of torpor leads to significant energy savings. The evaporative water loss of euthermic bats is relatively high, which seems unusual for a bat whose range includes extremely arid areas of Australia, and is reduced during torpor. The thermal conductance of euthermic C. gouldii is less than that predicted for a mammal of its size. The thermal conductance is considerably lower for torpid bats at intermediate body temperature and ambient temperature, but increases to euthermic values for torpid bats when thermoregulating at low ambient temperature. Accepted: 22 August 1996     

Behavioral and Physiological Thermoregulation of Crocodilians

Crocodilians, like other reptiles, regulate their body temperaturesby a combination of behavioral and physiological mechanisms.Behaviorally, they seek warm surface water or bask when cooland avoid overheating by the evaporation of water from theirdorsum, evaporation of water by gaping or by retreating to deep,cool water. Physiologically, crocodilians increase cutaneousthermal conductance by increasing blood flow to the skin (andsubdermal musculature) during warming. This hastens the warmingprocess. Cutaneous blood flow is reduced during general coolingand locally if the body temperature exceeds skin temperature.This enables crocodilians to increase body temperature significantlywhile basking in cool shallow water. Large crocodilians appearto be able to alter their rates of heat exchange to a largerextent than small ones and they can do so with less cardiovascularinvolvement. Large crocodilians, with their lower surface/volumeratio, are capable of producing sufficient metabolic heat toelevate their body temperature above water temperature.     

Oxygen consumption and body temperature in yellow-bellied marmot populations from montane-mesic and lowland-xeric environments

Summary Yellow-bellied marmots characteristically live in montane-mesic environments, but in several areas in western North America, this species extended its range into lowland-xeric habitats. Body mass was significantly smaller in the lowland-xeric population from eastern Washington at 393 m than in the montane-mesic population from western Colorado at 2900 m. Oxygen consumption of marmots from montane-mesic and lowland-xeric environments was signiflcantly affected by ambient temperature (T_A) water regimen, population, and a population x water regimen x temperature interaction. Lowland-xeric animals had a higher metabolic rate at low T_As, but a lower metabolic rate at higher T_As than the montane-mesic aminals. Oxygen consumption was lower on a restricted-water regimen than on ad libitum water in both populations. Coefficients relating oxygen consumption to body mass were affected by T_A, water regimen, and population. These intraspecific coefficients are larger than the interspecific coefficients for all mammals. Body temperature (T_B) was affected significantly by T_A, water regimen, and population. T_A body mass, and a population x water regimen interaction significantly affected conductance. Conductance generally was higher in the lowland-xeric than in the montane-mesic marmots. Both populations increased conductance at high T_A, but the lowland-xeric population dissipated a much higher proportion of the heat by evaporative water loss (EWL) than did the montane-mesic population. Metabolic water production exceeded or equaled EWL at 5–20°C. Smaller body size, reduced metabolism at high T_A, and increased EWL at high T_A characterized the lowland-xeric population.Metabolic rates of yellow-bellied marmots were higher than predicted from body size during the reproductive season but decreased to 67% of that predicted from the Kleiber curve by late summer. Marmots minimize thermoregulatory costs by concentrating activity at times when the microclimate is favorable, by tolerating hyperthermia at high T_A in the field, and by having a conductance lower than that predicted from body size.Abbreviations DHC dry-heat conductance - EHL evaporative heat loss - EWL evaporative water loss - HP heat produced - T _A ambient temperature - T _n body temperature - M body mass     

Thermal conductance and its relation to thermal time constants

A large body of thermoregulation studies exists in which the proper relationship between the physiological variable, thermal conductance, and heating or cooling time is not recognized. This is owing, in part, to conflicting definitions of conductance which either fail to relate to mean heat flow through the body surface or which fail to separate body conductance from that of the environment. Here we analyse ectotherm heating and cooling experiments to relate properly, conductance to thermal time constants and to determine how time constants are scaled according to animal size. It appears that the scaling properties are intimately related to peripheral circulation.Since thermal time constants can be unambiguously defined only for objects of constant thermal conductance we have provided simple illustratons of some phenomena related to temperature-dependent conductors and used these to indicate some of the limits of applicability of the time constant concept and its connection to conductance.Conditions described here do not include large radiant heat exchanges, however, convective heat transport and evaporation are considered. The treatment of evaporation should be quite useful to others.     

The importance of microhabitat in thermoregulation and thermal conductance in two namib rodents—a crevice dweller, Aethomys namaquensis, and a burrow dweller, Gerbillurus paeba

1. 1.|Thermoregulatory measurements of two Nambi rodents; Gerbillurus paeba, a burrow dweller, and Aethomys namaquensis, a crevice dweller were compared. Both were similar to other small arid-adapted rodents in that basal metabolic rates were reduced, thermoneutral zones narrow and evaporative water losses low. Rates of conductance and thermal lability, however, at ambient temperatures (T_a) below thermoneutral zone, were significantly different (P 0.01).

2. 2.|The rock rat A. namaquensis, living in a microclimate characterized by a large diel range and low humidities, compensates for a reduced basal metabolic rate by having a low rate of conductance. In this way it maintains precise thermoregulatory control. G. paeba, on the other hand, living in a thermally-stable milieu, does not control body temperature precisely. This animal instead utilizes a high rate of conductance to remove metabolic heat produced within the body. This would be advantageous to an animal living in a plugged burrow where the high humidities encountered impede the rate of evaporative cooling.

3. 3.|The energetic responses of both species, above the thermoneutral zone, appear to reflect very closely the environmental conditions which occur in the microhabitat that they rest in during the day. G. paeba shows less tolerance to temperature fluctuations than A. namaquensis, but shows more marked increases in short-term cooling mechanisms at high T_as.

4. 4.|Despite the increased use of evaporative cooling through salivation and panting in addition to pulmocutaneous evaporation, exposure to T_as above 38°C is rapidly lethal to G. paeba.

Convective and evaporative cooling in sawfly larvae

Responses to radiant and convective heat input were analysed in the gregarious larvae of Perga dorsalis (0·5-2·5 g body weight). Aggregating diminishes convective heat loss from each individual and augments the body temperature of larvae in the sun. Voluntary raising of the abdomen, occurring at body temperatures above about 30·4°C, increases convective heat loss. At body temperatures above about 37°C, a filtrate from the semiliquid midgut contents is excreted from the anus and spread over the body. This increases evaporative heat loss and maintains the body temperature below the critical thermal maximum (42°C) even when ambient temperature rises to 48°C. Based on the tolerance to water loss (17 per cent of the body weight) and the rates of evaporation, it is evident that evaporative cooling may be employed successfully throughout the hottest hours of the day.     

根田鼠的活动代谢率

在15～30℃温度范围内, 运用踏车呼吸室以5 m/min, 10 m/min 和15 m/min 的运动速度, 对栖息于青海高原的根田鼠的代谢率、体温、蒸发失水进行了测定, 并计算了每个温度和运动速度时的热传导率。根田鼠的体温在任一速度时, 随环境温度的增加而增加, 当环境温度一定时, 体温随运动强度而升高, 代谢率随运动速度增加而增加。活动产热在低温条件下, 可能是对寒冷产热的替代, 而在比较缓和的温度时, 可能是对冷诱导产热的附加。温度一定时, 蒸发失水随运动速度增加而增加, 热传导也呈相似的变化趋势(15℃除外)。热传导在任一运动速度下, 随环境温度增加而增加。结果表明蒸发散热在高温或活动期间对根田鼠的体温调节有不可替代的作用。     

The thermal and energetic significance of clustering in the speckled mousebird,Colius striatus

Summary The effect of clustering behaviour on metabolism, body temperature, thermal conductance and evaporative water loss was investigated in speckled mousebirds at temperatures between 5 and 36°C. Within the thermal neutral zone (approximately 30–35 °C) basal metabolic rate of clusters of two birds (32.5 J·g^-1·h^-1) and four birds (28.5 J·g^-1·h^-1) was significantly lower by about 11% and 22%, respectively, than that of individuals (36.4 J·g^-1·h^-1). Similarly, below the lower critical temperature, the metabolism of clusters of two and four birds was about 14% and 31% lower, respectively, than for individual birds as a result of significantly lower total thermal conductance in clustered birds. Body temperature ranged from about 36 to 41°C and was positively correlated with ambient temperature in both individuals and clusters, but was less variable in clusters. Total evaporative water loss was similar in individuals and clusters and averaged 5–6% of body weight per day below 30°C in individuals and below 25°C in clusters. Above these temperatures total evaporative water loss increased and mousebirds could dissipate between 80 and 90% of their metabolic heat production at ambient temperatures between 36 and 39°C. Mousebirds not only clustered to sleep between sunset and sunrise but were also observed to cluster during the day, even at high ambient temperature. Whereas clustering at night and during cold, wet weather serves a thermoregulatory function, in that it allows the brrds to maintain body temperature at a reduced metabolic cost, clustering during the day is probably related to maintenance of social bonds within the flock.Abbreviations BMR basal metabolic rate - bw body weight - C _totab total thermal conductance - EWI evaporative water loss - M metabolism - RH relative humidity - T _a ambient temperature - T _b body temperature - T _ch chamber temperature - T _cl cluster temperature - TEWL total evaporative water loss - LCT lower critical temperature - TNZ thermal neutral zone     

Thermoregulation and metabolism in the smallest African gerbil, Gerbillus pusillus

The effect of temperature on thermoregulation, metabolism, evaporative water loss and thermal conductance was studied in Gerbillus pusillus . Its resting body temperature (TB) was 34·6°C, approximately 5°C higher than the mean ambient temperature (TA) encountered in its burrow. As TA increased above 34°C, its ability to lose heat to the environment decreased. It overcame this problem by tolerating increases in TB to a non-lethal maximum of 41°C, whilst also eliminating increasing quantities of obligate heat by pulmocutaneous evaporation and conduction.
Metabolic rate was 41% lower than that predicted from Kleiber's (1975) allometric equation. This confers a considerable saving in energy in an environment where food is often scarce, whilst simultaneously reducing heat production and the degree of gaseous exchange in the already oxygen-poor and carbon dioxide-rich environment encountered in the plugged burrows of its natural milieu.
Gerbillus pusillus , therefore, does not maintain strict homeothermy and utilizes a labile TB and reduced metabolic rate as an adaptive mechanism for survival in the arid zones of tropical Africa.     

Diurnal variation in thermal and metabolic parameters of the golden hamster (Mesocricetus auratus)

The purpose of this study is to examine diurnal variation in several thermal and metabolic parameters of the golden hamster, Mesocricetus auratus. Metabolic rate, core temperature, and evaporative water loss were measured during night and day at several ambient temperatures. Wet minimal thermal conductance, dry minimal thermal conductance, basal metabolic rate, minimal net heat production and the lower critical temperature difference were estimated from these measurements. Wet and dry minimal thermal conductance, evaporative water loss, core temperature, basal metabolic rate, and lower critical temperature difference were greater during the active phase than during the resting phase. The diurnal variation in wet minimal thermal conductance was much smaller than that predicted from published allometric equations. The diurnal variation in wet minimal thermal conductance was 9% of the 24-h mean. The diurnal variation in dry minimal thermal conductance was 26% of the 24-h mean. The higher active-phase core temperature and basal metabolic rate may function to enhance peak metabolic performance during the active phase. The lower resting phase metabolism and core temperature may reduce energetic costs. The greater active-phase lower critical temperature difference may be a result of the greater active-phase basal metabolic rate. Diurnal variation in minimal thermal conductance may be caused by changes in peripheral circulation.Abbreviations BMR basal metabolic rate - T difference between core and ambient temperatures - T _1c lower critical temperature difference - EWL evaporative water loss - MTC minimal thermal conductance - MR metabolic rate - Q _ev evaporative heat loss - RQ respiratory quotient - T _a ambient temperature - T _c core temperature - T _1c lower critical temperature     

Physiological correlates of habitat association in East African sunbirds (Nectariniidae)

East African sunbirds (Nectariniidae) vary in the degree to which they use open habitats and forest habitats. Species that use open habitats may experience more extreme temperatures and greater exposure to solar radiation than those in forest habitats. Basal rates of metabolism, body temperature and thermal conductance were compared for open habitat- and forest-associated sunbirds from Kibale National Park, Uganda. Variation in basal rate of metabolism was associated with body mass, but there was no difference between forest and open habitat species. Variation in body temperature was not associated with body mass or habitat. Variation in thermal conductance was associated with body mass and habitat; open habitat species were characterized by significantly lower thermal conductances than forest species. Because reduced thermal conductance may decrease energy expenditure at low ambient temperatures and reduce exogenous heat gain at high ambient temperatures, this difference may optimize energy expenditure when temperatures are highly variable. This suggests a mechanism by which physiological characteristics may influence energetic consequences of habitat selection.     

The temperature and temperature gradients distribution in the rabbit body thermophysical model with evaporation of moisture from its surface

On created in laboratory heat-physical model of a rabbit body reflecting basic heat-physical parameters of the body such as: weight, size of a relative surface, heat absorption and heat conduction, heat capacity etc., a change of radial distribution of temperature and size was found across a superficial layer of evaporation of water from its surface, that simulates sweating, with various ratio of environmental temperature and capacity of electrical heater simulating heat production in animal. The experiments have shown that with evaporation of moisture from a surface of model in all investigated cases, there is an increase of superficial layer of body of a temperature gradient and simultaneous decrease of temperature of a model inside and on the surface. It seems that, with evaporation of a moisture from a surface of a body, the size of a temperature gradient in a thin superficial layer dependent in our experiments on capacity for heat production and environmental temperature, is increased and can be used in a live organism for definition of change in general heat content of the body with the purpose of maintenance of its thermal balance with environment.     

The development of thermoregulation in turkey and guinea fowl hatchlings: similarities and differences

The development of thermoregulation was studied in turkeys (Meleagris gallopavo, 60.5 g) and guinea fowl (Numida meleagris, 33.5 g) from 2 to 24 h after hatching. Thermoregulation was measured at different ages during 1 h of cold exposure (20°C). Final body temperature rose linearly with age in turkeys, but reached a plateau in guinea fowl between 12 and 16 h. At 2 h after hatch final body temperature was highest in guinea fowl, while at 24 h after hatch there was no difference between the species. The development of mass-specific metabolic rate with age resembled the pattern of final body temperature. At 2 h post-hatch mass-specific metabolic rate was highest in guinea fowl; however, at 24 h post-hatch there was no difference between the species. since mass-specific metabolic rate reached a plateau in guinea fowl at 16 h. In turkeys mass-specific dry thermal conductance decreased with age initially, while in guinea fowl it remained stable. Nevertheless, at both 2 and 24 h after hatch mass-specific wet conductance did not differ significantly between the species. In turkeys mass-specific wet conductance increased initially. This increase in mass-specific wet conductance may be due to the rapid onset of feather growth in turkeys. The O₂ consumption per breath doubled during the first 24 h in turkeys but remained stable in guine fowl. This suggests that at least two different developmental patterns of O₂ intake exist within Galliformes. The results show that 2 h post-hatch the thermoregulatory ability was lowest in turkeys, despite their larger body mass. However, at 24 h post-hatch the difference between the species was not significant, because the thermoregulatory ability had increased more in turkeys.Abbreviations B _f breathing frequency - BM body mass - BMR basal metabolic rate - C _D mass-specific dry thermal conductance - C _w mass-specific wet thermal conductance - HI homeothermy index - H _E evaporative heat loss - H _B loss of stored body heat - MR metabolic rate - M _MS mass-specific metabolic rate - RH relative humidity - I _A ambient temperature - T _Bi initial body temperature - T _Bf final body temperature - VO₂ volume oxygen consumed - VCO₂ volume carbon dioxide produced     

Body temperature and thermoregulation in two species of yellowjackets,Vespula germanica and V. maculifrons

In spite of the abundance and broad distribution of social wasps, little information exists concerning thermoregulation by individuals. We measured body temperatures of the yellowjackets Vespula germanica and V. maculifrons and examined their thermoregulatory mechanisms. V. germanica demonstrated thermoregulation via a decreasing gradient between thorax temperature and ambient temperature as ambient temperature increased. V. maculifrons exhibited a constant gradient at lower ambient temperatures but thorax temperature was constant at high ambient temperatures. Head temperature exhibited similar patterns in both species. In spite of low thermal conductances, a simple heat budget model predicts substantial heat loads in warm conditions in the absence of thermoregulation. Both species regurgitated when heated on the head. A smaller volume of regurgitant was produced at lower head temperatures and a larger volume at higher head temperatures. Small regurgitations resulted in stabilization of head temperature, while large ones resulted in 4°C decreases in head temperature. Regurgitation was rare when wasps were heated upon the thorax. Abdomen temperature was 3–4°C above ambient temperature, and approached ambient temperature under the hottest conditions. No evidence was found for shunting of hot hemolymph from thorax to abdomen as a cooling mechanism. The frequency of regurgitation in workers returning to the nest increased with ambient temperature. Regurgitation may be an important thermoregulatory strategy during heat stress, but is probably not the only mechanism used in yellowjackets.Abbreviations M _b body mass - M _th thorax mass - T _a ambient temperature - T _ab abdomen temperature - T _b body temperature - T _h head temperature - T _th thorax temperature - C _t thermal conductance     

Evaporative water loss in seven species of fossorial rodents: Does effect of degree of fossoriality and sociality exist?

In terrestrial endotherms, evaporation is a significant mechanism of water loss in hot environments. Although water is passively lost by evaporation, individuals can regulate it at different levels. Inhabiting a relatively stable environment characterized by mild ambient temperature (T_a) and high humidity can ensure a balanced water budget. Many fossorial rodents are well adapted to live in such conditions. In this study, evaporative water loss (EWL) of fossorial rodent species with different degree of adaptations to underground life (from strictly subterranean to those with regular surface activity) was evaluated. By measuring EWL, the specific contribution of either evaporative or non-evaporative components of heat loss can be determined. With the exception of the silvery mole-rat (Heliophobius argenteocinereus), in all tested rodents EWL is relatively stable below and within the thermoneutral zone (TNZ). As T_as increase above TNZ, EWL increases as does total thermal conductance, but conductance increases several times more than EWL. In addition, non-evaporative routes seem to be more important than evaporative heat loss in the analyzed species. No clear pattern of EWL in relation to a species degree of fossoriality or sociality was detected. In this context, atmosphere of burrows could affect EWL, since the high humidity found inside tunnels can establish limits on evaporation to favor water rather than thermal balance.     

Evaporative water loss: thermoregulatory requirements and measurements in the deer mouse and white rabbit

Summary Using a physical model of the capacity for non-evaporative heat loss and measurements of metabolic heat production, I evaluated the evaporative requirements for thermoregulation in the deer mouse,Peromyscus maniculatus, and the white rabbit,Oryctolagus cuniculus. The physical limit to non-evaporative heat loss was calculated from the heat transfer properties of the two animals and expressed as a maximum thermal conductance (C _max). Two physiologically-based thermal conductances were derived from evaporative water loss, respiratory gas exchange and core temperature measurements made between 8 and 34°C on the deer mouse, and taken from published data for the white rabbit. The thermal conductance for non-evaporative heat loss (C) was calculated from net heat production, whereasC _m represented the thermal conductance required to dissipate metabolic heat production. Evaporation is required when metabolic heat production exceeds the capacity for non-evaporative heat loss (as shown byC _m>C _max). However, evaporation increased in both animals although additional capacity to lose heat remained (i.e.,C<C _max). Evaporation increased withC above 30°C for the mouse and at each 5°C measurement interval from 15 to 30°C for the rabbit. Thus, evaporation was greater than that required for thermoregulation for both animals as determined from a physical model of heat loss because both evaporation andC increased together to regulate heat loss.Symbols: see list on title page of preceeding paper     

Body temperature and metabolic rate during natural hypothermia in endotherms

During daily torpor and hibernation metabolic rate is reduced to a fraction of the euthermic metabolic rate. This reduction is commonly explained by temperature effects on biochemical reactions, as described by Q ₁₀ effects or Arrhenius plots. This study shows that the degree of metabolic suppression during hypothermia can alternatively be explained by active downregulation of metabolic rate and thermoregulatory control of heat production. Heat regulation is fully adequate to predict changes in metabolic rate, and Q ₁₀ effects are not required to explain the reduction of energy requirements during hibernation and torpor.Abbreviations BMR basal metabolic rate - BW body weight - C thermal conductance - C_HL thermal conductance as derived from HL - C_HP thermal conductance as derived from HP - HL heat loss - HP heat production - MR metabolic rate - RQ respiratory quotient - T_a ambient temperature - T_b body temperature