Surviving the Cold, Dry Period in Africa: Behavioral Adjustments as an Alternative to Heterothermy in the African Lesser Bushbaby (Galago moholi)

Behavioral and physiological adaptations are common and successful strategies used by small endothermic species to adjust to unfavorable seasons. Physiological adaptations, such as heterothermy, e.g., torpor, are usually thought to be more effective energy-saving strategies than behavioral adjustments. The African lesser bushbaby, Galago moholi, is physiologically capable of torpor but expresses heterothermy only under conditions of extreme energy limitation, suggesting that it has evolved alternative strategies to compensate energetic bottlenecks. We hypothesized that Galago moholi survives the unfavorable winter period, without —or only rarely— employing torpid phases to save energy, by using behavioral thermoregulation. We compared the ecology and behavior of Galago moholi in summer and winter by telemetric tracking and examined food availability by determination of arthropod and gum availability. We found a significant increase in huddling behavior and a significant increase in the use of enclosed and insulated sleeping sites during winter, as well as a reduction in nightly activity. Galago moholi hunted for insects significantly less in winter than in summer, and increased gum intake in winter, when gum showed an increase in energy content. The availability of high-quality food, albeit in low quantities, presumably enables Galago moholi to stay normothermic throughout the cold, dry period and to focus on reproduction activities. We propose that Galago moholi favors ecological and behavioral adjustments over torpor because these are sufficient to meet energy requirements of this species, and their advantages (flexibility, unrestricted activity, and reproduction) outweigh the energetic benefits of heterothermy.     

Some like it cold: summer torpor by freetail bats in the Australian arid zone

Bats are among the most successful groups of Australian arid-zone mammals and, therefore, must cope with pronounced seasonal fluctuations in ambient temperature (T _a), food availability and unpredictable weather patterns. As knowledge about the energy conserving strategies in desert bats is scant, we used temperature-telemetry to quantify the thermal physiology of tree-roosting inland freetail bats (Mormopterus species 3, 8.5 g, n = 8) at Sturt National Park over two summers (2010–2012), when T _a was high and insects were relatively abundant. Torpor use and activity were affected by T _a. Bats remained normothermic on the warmest days; they employed one “morning” torpor bout on most days and typically exhibited two torpor bouts on the coolest days. Overall, animals employed torpor on 67.9 % of bat-days and torpor bout duration ranged from 0.5 to 39.3 h. At any given T _a, torpor bouts were longer in Mormopterus than in bats from temperate and subtropical habitats. Furthermore, unlike bats from other climatic regions that used only partial passive rewarming, Mormopterus aroused from torpor using either almost entirely passive (68.9 % of all arousals) or active rewarming (31.1 %). We provide the first quantitative data on torpor in a free-ranging arid-zone molossid during summer. They demonstrate that this desert bat uses torpor extensively in summer and often rewarms passively from torpor to maximise energy and water conservation.     

Torpor is not the only option: seasonal variations of the thermoneutral zone in a small primate

The reddish-gray mouse lemur (Microcebus griseorufus) is one of only a few small mammals inhabiting the spiny forest of southwestern Madagascar. In this study we investigated the physiological adjustments which allow these small primates to persist under the challenging climatic conditions of their habitat. To this end we measured energy expenditure (metabolic rate) and body temperature of 24 naturally acclimatized mouse lemurs, kept in outdoor enclosures, during different seasons (summer, winter, and the transition period between the two seasons). Mouse lemurs displayed two main physiological strategies to compensate seasonal and diurnal fluctuations of ambient temperature. On the one hand, individuals entered hypometabolism with decreasing ambient temperature (T _a) during the transition period and winter, enabling them to save up to 21 % energy per day (92 % per hour) compared with the normal resting metabolic rate at comparable T _a. On the other hand, euthermic mouse lemurs also showed physiological adjustments to seasonality when resting: the lower critical temperature of the thermoneutral zone decreased from summer to winter by 7.5 °C, which allowed mouse lemurs to keep energy demands constant despite colder T _as during winter. In addition, the basal metabolic rate was substantially lowered prior to the winter period, which facilitated accumulation of fat reserves. The combination of physiological modifications during euthermia in addition to hypometabolism, which can be individually adjusted according to external parameters and respective body condition, is important as it allows M. griseorufus to cope with the environmental variability of an energetically challenging habitat.     

Does fear beget fear? Risk-mediated habitat selection triggers predator avoidance at lower trophic levels

Seasonal changes in weather and food availability differentially impact energy budgets of small mammals such as bats. While most thermal physiological research has focused on species that experience extreme seasonal temperature variations, knowledge is lacking from less variable temperate to subtropical climates. We quantified ambient temperature (T _a) and skin temperature (T _sk) responses by individuals from a population of New Zealand lesser short-tailed bats (Mystacina tuberculata) during summer and winter using temperature telemetry. During summer, communal roosts were more thermally stable than T _a. During winter, solitary roosts were warmer than T _a indicating significant thermal buffering. Communal roost trees were used on 83 % of observation days during summer, and individuals occupying them rarely entered torpor. Solitary roosts were occupied on 93 % of observation days during winter, and 100 % of individuals occupying them used torpor. During summer and winter, bats employed torpor on 11 and 95 % of observation days, respectively. Maximum torpor bout duration was 120.8 h and winter torpor bout duration correlated negatively with mean T _a. Torpor bout duration did not differ between sexes, although female minimum T _sk was significantly lower than males. The summer Heterothermy Index varied, and was also significantly affected by T _a. Mean arousal time was correlated with sunset time and arousals occurred most frequently on significantly warmer evenings, which are likely associated with an increased probability of foraging success. We provide the first evidence that torpor is used flexibly throughout the year by M. tuberculata, demonstrating that roost choice and season impact torpor patterns. Our results add to the growing knowledge that even small changes in seasonal climate can have large effects on the energy balance of small mammals.     

Continuous growth through winter correlates with increased resting metabolic rate but does not affect daily energy budgets due to torpor use

Small mammals that are specialists in homeothermic thermoregulation reduce their self-maintenance costs of normothermy to survive the winter. By contrast, heterothermic ones that are considered generalists in thermoregulation can lower energy expenditure by entering torpor. It is well known that different species vary the use of their strategies to cope with harsh winters in temperate zones; however, little is still known about the intraspecific variation within populations and the associated external and internal factors. We hypothesized that yellow-necked mice Apodemus flavicollis decrease their resting metabolic rate (RMR) from autumn to winter, and then increase it during spring. However, since the alternative for seasonal reduction of RMR could be the development of heterothermy, we also considered the use of this strategy. We measured body mass (m_b), RMR, and body temperature (T_b) of mice during 2 consecutive years. In the 1st year, mice decreased whole animal RMR in winter, but did not do so in the 2nd year. All mice entered torpor during the 2nd winter, whereas only a few did so during the first one. Mice showed a continuous increase of m_b, which was steepest during the 2nd year. The relationship between RMR and m_b varied among seasons and years most likely due to different mouse development stages. The m_b gain at the individual level was correlated positively with RMR and heterothermy. This indicates that high metabolism in winter supports the growth of smaller animals, which use torpor as a compensatory mechanism. Isotope composition of mice hair suggests that in the 1st year they fed mainly on seeds, while in the 2nd, they likely consumed significant amounts of less digestible herbs. The study suggests that the use of specialist or generalist thermoregulatory strategies can differ with environmental variation and associated differences in developmental processes.     

Seasonal changes in energetics and torpor patterns in the subtropical blossom-bat Syconycteris australis (Megachiroptera)

Little is known about how animals from tropical and subtropical climates adjust their energy expenditure to cope with seasonal changes of climate and food availability. To provide such information, we studied the thermal physiology, torpor patterns and energetics of the nocturnal blossom-bat (Syconycteris australis 18 g) from a subtropical habitat in both summer and winter. In both seasons, S. australis frequently entered daily torpor at ambient temperatures between 12 and 25°C when food and water were withheld. Unlike patterns observed in temperate animals, mean minimum metabolic rates during torpor were lower in summer (0.47 ± 0.07 ml O₂ g⁻¹ h⁻¹) than in winter (0.75 ± 0.11 ml O₂ g⁻¹ h⁻¹). Body temperatures during torpor were regulated at 19.3 ± 1.0°C in summer and at 23.4 ± 2.0°C in winter. Torpor bout duration was significantly longer in summer (7.3 ± 0.6 h) than in winter (5.5 ± 0.3 h), but in both seasons, bout duration was not affected by ambient temperature. Consequently, average daily metabolic rates were also significantly lower in summer than in winter. Body temperatures and metabolic rates in normothermic bats did not change with season. Our findings on seasonal changes of torpor in this bat from the subtropics are opposite to those made for many species from cold climates which generally show deeper and longer torpor in winter and are often entirely homeothermic in summer. More pronounced torpor in subtropical S. australis in summer may be due to low or unpredictable nectar availability, short nights which limit the time available for foraging, and long days without access to food. Thus, the reversed seasonal response of this subtropical bat in comparison to temperate species may be an appropriate response to ecological constraints. Received: 6 May 1997 / Accepted: 19 October 1997     

The effect of seasonal food restriction on activity, metabolism and torpor in the South African hedgehog (Atelerix frontalis)

Twelve South African hedgehogs (Atelerix frontalis) were subjected to nine-week experimental protocol comprising four weeks of simulated summer conditions (14L: 10D and 25 °C), and transition week followed by four weeks of simulated winter conditions (10L: 14D and 15 °C).
Six control hedgehogs, with access to food ad libitum throughout the experiment, did not increase their energy intake during winter yet retained stable body mass. Six experimental hedgehogs, of similar body size, experienced restricted diet during the last three weeks of each season. These hedgehogs displayed significantly lower energy intake than controls during food restriction and lost approximately 7% of their body weight in both seasons, although this weight loss was not significant.
Both groups displayed lower digestive efficiencies in winter, together with decline in activity. However, there remained no significant effect of food restriction on these parameters.
Neither control nor experimental hedgehogs displayed torpor during summer and, whilst both groups became torpid in winter, the duration of torpor was significantly longer in experimental hedgehogs following food restriction.
Analysis of fluctuations in body mass suggest that experimental hedgehogs supplemented their restricted diet with energy derived from body reserves during both seasons. However, the ability of this species to modify the duration of torpor in response to additional energetic stress indicates that A. frontalis can control its energetic expenditure in order to limit the depletion of body reserves.     

Seasonal acclimation of preferred body temperatures improves the opportunity for thermoregulation in newts

Seasonal acclimation and thermoregulation represent major components of complex thermal strategies by which ectotherms cope with the heterogeneity of their thermal environment. Some ectotherms possess the acclimatory capacity to shift seasonally their thermoregulatory behavior, but the frequent use of constant acclimation temperatures during experiments and the lack of information about thermal heterogeneity in the field obscures the ecological relevance of this plastic response. We examined the experimentally induced seasonal acclimation of preferred body temperatures (T(p)) in alpine newts Ichthyosaura (formerly Triturus) alpestris subjected to a gradual increase in acclimation temperature from 5°C during the winter to a constant 15°C or diel fluctuations between 10° and 20°C during the spring/summer. Both the mean and range of T(p) followed the increase in mean acclimation temperature without the influence of diel temperature fluctuations. The direction and magnitude of this acclimatory capacity has the potential to increase the time window available for thermoregulation. Although thermoregulation and thermal acclimation are often considered as separate but coadapted adjustments to thermal heterogeneity, their combined response is employed by newts to tackle seasonal variation in a thermoregulatory-challenging aquatic environment.     

Seasonal thermoregulation in the burrowing parrot (Cyanoliseus patagonus)

Birds exposed to seasonal environments are faced with the problem of maintaining thermogenic homoeostasis. Previous studies have established that birds native to the Holarctic increase their Resting Metabolic Rate at different ambient temperatures (RMR_Ta) and Basal Metabolic Rate (BMR) in winter as an adaptation to cold temperature since winters are more severe, while their non-Holarctic counterparts generally decrease their winter BMR as an energy saving mechanism during unproductive and dry winter months. In this study, we examined seasonal thermoregulation in the burrowing parrot (Cyanoliseus patagonus), a colonial psittacine native to the Patagonian region of Argentina, a region with an unpredictable environment. We found significantly higher mass specific RMR_Ta and BMR in summer than in winter. Both summer and winter BMR of the species fell within the predicted 95% confident interval for a parrot of its size. Body mass was significantly higher in winter than in summer. The burrowing parrot had broad thermo-neutral zones in winter and summer. The circadian rhythm of core body temperature (T_b) of burrowing parrots was not affected by season, showing that this species regulated its T_b irrespective of season. These results suggest that the burrowing parrots' seasonal thermoregulatory responses represent that of energy conservation which is important in an unpredictable environment.     

Seasonal changes of thermoregulatory efficiency in Djungarian hamsters

In their natural habitat, Djungarian hamsters are faced with dramatic seasonal changes. This requires various morphological and physiological adaptations allowing cope with harsh climate and food shortage, particularly in winter. These seasonal changes are controlled by the photoperiod and can be observed also in the laboratory at room temperature. The aim of the present study was to investigate if the efficiency of thermoregulation also depends on the photoperiod. For this reason, Djungarian hamsters were transferred to short-day conditions (SDC) with 8 h light and 16 h darkness. Two-thirds of the animals were classified as responders showing the typical seasonal changes – decrease of body mass, fur change, testes regression, vagina closing. The total activity per day did not change but, the nocturnal activity was spread over the longer dark time. The body temperature decreased, and the animals showed regular daily torpor. To investigate the thermoregulatory efficiency, body temperatures were correlated with motor activity. The obtained regression coefficients describe formally the effect of motor activity on body temperature, a measure for the efficiency of thermoregulation. In SDC, the coefficients were elevated, both during rest and activity, i.e. the same amount of activity did produce a larger increase in body temperature. Under field conditions, this might be an additional mechanism to compensate the bigger in winter heat loss. Also, the high coefficients may support the increase in body temperature at the end of a torpor phase by a bout of motor activity. The results show that, seasonal changes of thermoregulatory efficiency are an effective accessory way to cope with different temperatures in hamsters’ natural environment.     

Daily torpor in free-ranging rock elephant shrews, Elephantulus myurus: a year-long study

Under laboratory conditions, rock elephant shrews, Elephantulus myurus, use daily torpor under both short and long photoperiod acclimation. However, use of heterothermy often differs under field and laboratory conditions. We investigated the use of torpor in free-ranging elephant shrews from May 2001 to May 2002. The elephant shrews were capable of daily torpor throughout the year, with torpor most prevalent during winter. We recorded two torpor bouts during early summer (November). We recorded a total of 467 torpor bouts during the year. The mean torpor minimum body temperature (Tbmin) for the whole year was 15.3 degrees +/-4.4 degrees C, and the mean bout length was 8.6+/-3.5 h. These values were in the range expected for daily heterotherms. However, there was some marginal overlap with hibernation characteristics; a few torpor bouts were longer than 24 h in duration, and Tbmin decreased below 10 degrees C. Torpor was highly correlated with low ambient temperature and photoperiod. Torpor was also correlated with invertebrate abundance after controlling for photoperiod effects. During the year in which this study was conducted, the rainfall was 14% below long-term average. Historical rainfall records show that summer rainfall during strong El Nino years is up to 40% below the long-term average. During these drought years, the frequency of summer torpor may be higher, highlighting the need for long-term physiological data in free-ranging animals.     

Regulated hypothermia in the desert shrew

Summary Desert shrews (Notiosorex crawfordi; 4 g) enter into daily bouts of very shallow torpor, when restricted in their food intake. These bouts, though interrupted and uneven, last throughout that portion of the day the animals' cages are lighted. Body temperature is apparently regulated by fine adjustments of metabolic heat production in hypothermic as well as euthermic desert shrews. Thus, these animals seem to have two temperature thresholds for thermoregulation or body temperature rheostat settings. One is near 38 °C while the other, near 28 °C is likely used exclusively when energy supplies are low. The coefficient of heat transfer is the same at both body temperatures. Power saved by hypothermic animals at air temperatures between 20 and 25 °C amounts to about 96 mW. This is half of the metabolic power output of euthermic shrews at 20 °C and 80% at 25 °C. These results suggest a compromise between the energy savings of a deep torpor and the unimpaired functioning of euthermia.Supported by NSF: DEB 75-18576 and NIH: AM 05738     

Black or white? Physiological implications of roost colour and choice in a microbat

Although roost choice in bats has been studied previously, little is known about how opposing roost colours affect the expression of torpor quantitatively. We quantified roost selection and thermoregulation in a captive Australian insectivorous bat, Nyctophilus gouldi (n=12) in winter when roosting in black and white coloured boxes using temperature-telemetry. We quantified how roost choice influences torpor expression when food was provided ad libitum or restricted in bats housed together in an outdoor aviary exposed to natural fluctuations of ambient temperature. Black box temperatures averaged 5.1 °C (maximum 7.5 °C) warmer than white boxes at their maximum daytime temperature. Bats fed ad libitum chose black boxes on most nights (92.9%) and on 100% of nights when food-restricted. All bats used torpor on all study days. However, bats fed ad libitum and roosting in black boxes used shorter torpor and spent more time normothermic/active at night than food-restricted bats and bats roosting in white boxes. Bats roosting in black boxes also rewarmed passively more often and to a higher skin temperature than those in white boxes. Our study suggests that N. gouldi fed ad libitum select warmer roosts in order to passively rewarm to a higher skin temperature and thus save energy required for active midday rewarming as well as to maintain a normothermic body temperature for longer periods at night. This study shows that colour should be considered when deploying bat boxes; black boxes are preferable for those bats that use passive rewarming, even in winter when food availability is reduced.     

Torpor characteristics and energy requirements of furless Siberian hamsters.

After approximately 10 wk of exposure to decreasing day lengths, Siberian hamsters (Phodopus sungorus) begin to display spontaneous torpor bouts several times each week. Torpor is associated with reduced daily energy expenditure and lower food consumption and ameliorates the thermoregulatory challenges of winter. We tested the extent to which the energy savings conferred by daily torpor depend on the presence of an insulative pelage. Female hamsters were housed in a winter day length (8L:16D) at 5 degrees C; daily food intake and torpor characteristics were recorded for 5 wk in shaved (furless) or normal hamsters. Torpor-bout incidence decreased by 62% in furless hamsters, but the duration of individual bouts and the minimum body temperature attained during torpor were unaffected by loss of pelage. Body temperature declined more rapidly during entry into torpor and increased more slowly during arousal from torpor in furless than in control hamsters. Energy savings per torpor bout, assessed by the amount of food consumed on days that included a torpor bout, was substantially greater in normal than in furless hamsters (16.0% vs. 3.3%); this difference likely reflects the increased cost of thermoregulation during torpor, as well as the increased caloric expenditure incurred by furless hamsters during arousal from torpor. An insulative pelage may be a prerequisite for the energetic benefits derived from heterothermy in this species.     

Plasticity in body temperature and metabolic capacity sustains winter activity in a small endotherm (Rattus fuscipes)

Small mammals that remain active throughout the year at a constant body temperature have a much greater energy and food requirement in winter. Lower body temperatures in winter may offset the increased energetic cost of remaining active in the cold, if cellular metabolism is not constrained by a negative thermodynamic effect. We aimed to determine whether variable body temperatures can be advantageous for small endotherms by testing the hypothesis that body temperature fluctuates seasonally in a wild rat (Rattus fuscipes); conferring an energy saving and reducing food requirements during resource restricted winter. Additionally we tested whether changes in body temperature affected tissue specific metabolic capacity. Winter acclimatized rats had significantly lower body temperatures and thicker fur than summer acclimatized rats. Mitochondrial oxygen consumption and the activity of enzymes that control oxidative (citrate synthase, cytochrome c-oxidase) and anaerobic (lactate dehydrogenase) metabolism were elevated in winter and were not negatively affected by the lower body temperature. Energy transfer modeling showed that lower body temperatures in winter combined with increased fur thickness to confer a 25 kJ day^? 1 energy saving, with up to 50% owing to reduced body temperature alone. We show that phenotypic plasticity at multiple levels of organization is an important component of the response of a small endotherm to winter. Mitochondrial function compensates for lower winter body temperatures, buffering metabolic heat production capacity.     

Thyroid hormone status affects expression of daily torpor and gene transcription in Djungarian hamsters (Phodopus sungorus)

Thyroid hormones (TH) play a key role in regulation of seasonal as well as acute changes in metabolism. Djungarian hamsters (Phodopus sungorus) adapt to winter by multiple changes in behaviour and physiology including spontaneous daily torpor, a state of hypometabolism and hypothermia. We investigated effects of systemic TH administration and ablation on the torpor behaviour in Djungarian hamsters adapted to short photoperiod. Hyperthyroidism was induced by giving T4 or T3 and hypothyroidism by giving methimazole (MMI) and sodium perchlorate via drinking water. T3 treatment increased water, food intake and body mass, whereas MMI had the opposite effect. Continuous recording of body temperature revealed that low T3 serum concentrations increased torpor incidence, lowered T_b and duration, whereas high T3 serum concentrations inhibited torpor expression. Gene expression of deiodinases (dio) and uncoupling proteins (ucp) were analysed by qPCR in hypothalamus, brown adipose tissue (BAT) and skeletal muscle. Expression of dio2, the enzyme generating T3 by deiodination of T4, and ucps, involved in thermoregulation, indicated a tissue specific response to treatment. Torpor per se decreased dio2 expression irrespective of treatment or tissue, suggesting low intracellular T3 concentrations during torpor. Down regulation of ucp1 and ucp3 during torpor might be a factor for the inhibition of BAT thermogenesis. Hypothalamic gene expression of neuropeptide Y, propopiomelanocortin and somatostatin, involved in feeding behaviour and energy balance, were not affected by treatment. Taken together our data indicate a strong effect of thyroid hormones on torpor, suggesting that lowered intracellular T3 concentrations in peripheral tissues promote torpor.     

Seasonality of torpor and thermoregulation in three dasyurid marsupials

Summary Seasonal variation in the pattern of torpor and temperature regulation was investigated in the closely related arid zone dasyurid marsupialsSminthopsis crassicaudata (17 g),S. macroura (24 g), andDasyuroides byrnei (120 g). The tendency to enter torpor was greater, torpor commenced earlier, torpor duration was longer, and body temperatures (T _b) were lower inSminthopsis spp. than inD. byrnei. The minimum mass-specific rate of oxygen consumption ( ) of torpid animals was similar among the three species despite the differences in minimumT _b. The mass-specific oxygen consumption of normothermic animals was reduced during winter when compared with the summer values in all species, but there was no seasonal variation in normothermicT _b in any species. The tendency to enter torpor was incrased during winter. TorpidSminthopsis spp. had lower values ofT _b and during winter than during summer;D. byrnei did not show seasonal changes in these variables. These results suggest that seasonal changes in the pattern of thermoregulation and torpor in small dasyurids may be more distinct than in larger species.Abbreviations RMR resting metabolic rate - BMR basal metabolic rate     

Seasonal torpor and normothermic energy metabolism in the Eastern chipmunk (Tamias striatus)

To assess the changes in thermoregulatory characteristics that accompany the seasonal expression of torpor we measured seasonal differences in body mass adjustments, body temperature (T _b) and metabolic rate (MR) in both summer- and winter-acclimated individuals from a species of food-storing hibernator, the Eastern chipmunk (Tamias striatus). Torpor occurred only in the winter and was associated with lower normothermic T _b, during inter-bout arousal periods than in the summer. Chipmunks increased body mass before the initiation of torpor in winter, and steadily lost mass as the hibernation season progressed. Torpor expression was correlated to initial mass gain, with the individuals who showed the largest mass increase in the fall showing the highest degree of torpor. Acclimation to winter-like conditions produced a decline in normothermic MR at all ambient temperatures examined. The findings indicate that torpor expression is accompanied by a decrease in T _b and MR during normothermy, indicating that a conservation of energy metabolism occurs, not only in torpor, but also during the inter-bout arousal periods.     

Seasonal control of energy requirements for thermoregulation in the djungarian hamster (Phodopus sungorus), living in natural photoperiod

Summary Djungarian dwarf hamsters,Phodopus s. sungorus, were kept in natural photoperiodic conditions throughout the year, either inside at a constantT _a of 23°C or outside subjected to seasonally varyingT _a. Comparisons were made between hamsters from both conditions to evaluate the significance of seasonal changes in photoperiod and/orT _a as environmental cues for seasonal acclimatization inPhodopus. Basal metabolic rate was lowest in July (1.68 ml/g·h) and highest in January (2.06 ml/g·h inPhodopus living outside), combined with a decrease inT _1c from 26°C in July to 20°C in January. This was parallelled by seasonal changes in body weight (summer 42 g, winter 25g), fur colouration, fur depth and the occurrence of short daily torpor.AtT _a below thermoneutrality total energy requirements for thermoregulation in winter acclimatizedPhodopus were found 36% lower than summer values (e.g. at O°CT _a in summer 1,160 mW, in winter 760 mW), which were effected by a combined strategy of reducing body weight (19%) together with improvements of thermal insulation of the body surface (17%). All seasonal changes were similar inPhodopus living inside or outside, suggesting that seasonal changes in photoperiod and not seasonal changes inT _a is the overriding controller for the environmental cueing of seasonality in energy requirements for thermoregulation.This research was supported by the Deutsche Forschungsgemeinschaft (He 990)     

Seasonal variation in metabolic rate of a medium-sized frugivore, the Knysna Turaco (Tauraco corythaix)

Many seasonal thermoregulation studies have been conducted on Holarctic birds that live in predictable, highly seasonal climates with severe winters. However, relatively few studies have been conducted on their southern hemisphere Afrotropical counterparts that encounter less predictable climates with milder winters. These latter birds are expected to conserve energy in winter by downregulating their metabolic rates. Therefore in this study, metabolic rate was measured during summer and winter in Knysna Turaco, Tauraco corythaix (Musophagiformes, Musophagidae) (c. 310 g), a non-passerine, in order to test whether there is energy conservation in winter. No overall significant differences in resting metabolic rates over a range of ambient temperatures were observed between winter and summer. However, whole-organism basal metabolic rates were 18.5% higher (p=0.005) in winter than in summer (210.83±15.97 vs. 186.70±10.52 O₂ h⁻¹). Knysna Turacos had broad thermoneutral zones ranging from 20 to 28 °C in winter and 10 to 30 °C in summer. These results suggest that Knysna Turacos show seasonal thermoregulatory responses that represent cold defense rather than energy conservation, which is contrary to what was expected.