Thyroxine affects behavioral thermoregulation but not growth rate among populations of the western fence lizard (Sceloporus occidentalis)

We investigated whether thyroxine influences hatchling growth rate of the western fence lizard (Sceloporus occidentalis) throught its effects on thermoregulatory behaviors. We reared control and thyroxine-injected hatchlings from three populations of S. occidentalis that differ in growth rate in a thermal gradient. We also measured the daily changes in body temperature and activity level (proportion of time spent out of retreat sites) of control and thyroxine-injected lizards. Previous studies have shown that within and among population differences in growth rate of the western fence lizard are correlated with the maintenance of high activity levels (proportion of time spent outside of retreat sites) and high body temperatures throughout the day. Growth rate was not influenced by injections of thyroxine. However, injections of thyroxine did elevate average daily body temperature and daily activity. Although administration of thyroxine uniformly increased the probability of activity throughout the day, it did not appear to alter the daily changes in activity. Previous studies have shown that the slower-growing hatchlings from northern populations exhibit a decline in activity during the later part of the thermal cycle, whereas the faster growing southern hatchlings maintain the same level of high activity throughout the thermal cycle. The decline in activity of northern populations was not prevented by thyroxine injection used in our current study. Northern lizards receiving exogenous thyroxine were still less active later in the day compared to early in the day, even though activity level throughout the day was elevated. Thus, the effects of thyroxine on temperature regulation observed in our study (general increase in activity level) appear to be unrelated to those aspects of temperature regulation (e.g., daily changes in behavioral thermoregulation) that are correlated with among population differences in growth rate. We also raised hatchlings in a cycling thermal regime (forced thermal cycle of 34°C:15°C, 12L:12D) where behavioral thermoregulation is not possible. The growth rate of lizards forced to cycle between 34°C:15°C on a daily basis was significantly lower than those lizards allowed to behaviorally thermoregulate, further underscoring the importance of the circadian pattern of thermoregulation for growth.Abbreviations GR growth rate - MR metabolic rate - SMR standard metabolic rate - SVL snout-vent length - T₄ thyroxine - T _b body temperature - T _e environmental temperature     

Interrelations Among Water and Energy Relations of Reptilian Eggs, Embryos, and Hatchlings

Reptilian eggs previously categorized with respect to the flexibilityof eggshells appear to fall into two groups: endohydric eggsare those that are invested, by the female parent at the timeof oviposition, with all of the water necessary to completeembryogenesis; and ectohydric eggs which need to absorb waterfrom the nest medium tocomplete embryogenesis. Eggs of the Galapagosland iguana are unusual among most lepidosaurians by havingvery permeable parchment shells, but containing a large albumen(apparently serving as a reservoir of water for the embryo).It appears that the eggs of Galapagos land iguanas can exploitan endohydric habit without the rigid, impermeable shell seenin other endohydric eggs. This ability appears to be mediatedby two factors: eggs of Galapagos land iguanas are laid in drysoils which are essentially impermeable to water, and the verylarge eggs of land iguanas have a relatively small surface areatovolume ratio which results in a relatively small exchangeof water across the eggshell. It appears too that the waterrelations of Galapagos land iguana eggs will affect the energeticsof both the contained embryo and the subsequent hatchling. Withoutadequate water, land iguana eggs will produce hatchlings thatare both smaller and possess less fat to sustain thejuvenileduring the first year of life.     

Ontogenetic changes in food intake and digestion rate of the herbivorous marine iguana (Amblyrhynchus cristatus,Bell)

Young reptiles have higher relative energy demands than adults, but the proposed ontogenetic changes in diet to fulfil these demands were not found in the algae-eating Galápagos marine iguanas on Santa Fé. Feeding and digestion rates were investigated to analyse how young achieve higher energy intake. Daily food intake of free ranging marine iguana hatchlings (6–11 months old) was about one third that of adults, but relative intake (g dry mass · g^–1 wet mass · day^–1) was four times higher in the hatchlings. During feeding experiments, relative daily food intake of hatchling marine iguanas was approximately three times higher than that of adults (0.042 vs 0.013 g dry mass · g^–0.8 wet mass · day^–1), and mean gut passage time was two times shorter (5 vs 10 days). The hatchlings also maintained high body temperatures (36.7° C) even under relatively cool day-time air temperatures of 32° C. Apparent digestibility of algal food measured both during feeding trials and by Mn²⁺ AAS (atomic absorption spectrometry) for free-ranging iguanas was 70%, independent of body size and temperature. The red algae prevailing in the diet were high in protein (30% dry mass) and energy (12.1 kJ/g dry mass). Diving iguanas had higher rates of energy intake than intertidal foragers, but daily intake was less. Maintenance of high body temperature enabled hatchlings to achieve high digestion rates and, combined with high relative intake, thus achieve sufficient energy intake for rapid growth despite higher mass specific metabolic rates. Estimates of biomass of marine iguanas and their algal food are given for a section of coastline on Santa Fé.     

Evaluating thermal resource partitioning

Summary The field thermal biology of sympatric Anolis cooki and A. cristatellus were evaluated in January and in August in desert scrub forest at Playa de Tamarindo near Guanica, Puerto Rico. Data on randomly positioned copper models of lizards, each equipped with a built-in thermocouple, established null hypotheses about basking frequency and operative temperatures (T _e) against which the behavior and body temperatures (T _b) of live lizards were evaluated. Both species exhibited non-random hourly basking rates (more marked in cristatellus than in cooki), and cristatellus was virtually inactive during the warm mid-day hours. The relationship between lizards' T _b and randomly sampled T _e differed between the species: cristatellus's mean T _b was 2° to 3° C lower than randomly sampled mean T _e in both months, whereas cooki's mean T _b was slightly higher than mean T _e in January and slightly lower in August. Although cooki's mean T _b was higher than that of cristatellus in both months, the T _b's of the two species overlapped substantially over an annual cycle. Given the similarities in their field active T _b and the low thermal heterogeneity among microsites at Playa de Tamarindo, these species appear not to partition the thermal environment there in a coarse-grained way. Instead, the relatively small differences in their field active T _b probably result from small differences in their use of similar microhabitats within their mutually exclusive territories. Thermal resource partitioning by territorial animals is unlikely unless thermal heterogeneity is coarse-grained in relation to territory size.     

Thermal preferences of hatchling saltwater crocodiles (Crocodylus porosus) in response to time of day,social aggregation and feeding

Three month old hatchling Crocodylus porosus with data loggers in their stomachs were placed in thermal gradients, in isolation (N=16) and in groups of 4 (N=8 groups; 32 individuals). Mean T_b and variation in T_b (SD) was not different whether individual crocodiles in isolation were fasted or fed, or if individuals were housed in isolation (I) or in groups (G). However, individuals in isolation (N=16) maintained slightly lower T_bs than those in groups (N=32) during the early morning (06:00–11:00 h). The overall mean T_b recorded for fasted individuals in the isolated and group treatments (N=48) was 30.9±2.3 °C SD, with 50% of T_bs (T_set) between 29.4 °C and 32.6 °C, and a voluntary maximum and minimum of 37.6 °C and 23.2 °C respectively. During the day (11:00–17:00 h), individuals in isolation and in groups selected the warmer parts of the gradient on land, where they moved little. Outside of this quiescent period (QP), activity levels were much higher and they used the water more. There was a strong diurnal cycle for fasted individuals in isolation and in groups, with T_b during the QP (31.9±2.09 °C; N=48) significantly higher than during the non-quiescent period (NQP: 30.6±2.31 °C). Thermal variation (SD) in T_b was relatively stable throughout the day, with the highest variation at around dusk and early evening (18:00–20:00 h), which coincided with a period of highest activity. The diurnal activity cycle appears innate, and may reflect the need to engage in feeding activity at the water's edge in the early evening, despite ambient temperatures being cooler, with reduced activity and basking during the day. If so, preferred T_b may be more accurately defined as the mean T_b during the QP rather than the NQP. Implications for the thermal environment best suited for captive C. porosus hatchlings are discussed.     

Comparative thermal ecology of two lizards

Summary In a habitat judged to be energetically costly for thermoregulation, mean body temperatures (MBT's) ofAnolis sagrei are significantly higher than those ofA. distichus. As indexed by the slope of the regression of body temperatures (T _b ) on substrate temperature (T _s ),A. sagrei is more dependent upon environmental temperatures thanA. distichus.In a habitat judged to be less costly for thermoregulation and where interspecific competition for perch sites may be less, MBT's ofA. sagrei are significantly higher, proportionally more lizards occupy sunny perches, and the slope of the regression of T _b on T _s is significantly less, than for conspecifics in the costly habitat.As indexed by length-specific fat body weights, well-nourished lizards in the costly habitat have T _b 's which are independent of environmental temperature; T _b 's of poorly-nourished lizards are highly dependent upon environmental temperature. This relationship does not hold for lizards in the low-cost habitat.These results corroborate the hypothesis that energetic costs are important in controlling the extent to which lizards thermoregulate. In high-cost habitats lizards thermoregulate less precisely than in low-cost habitats. Lizards that exploit the habitat as if it were highly productive thermoregulate more precisely than lizards that exploit the environment as if it were of low productivity.     

Evidence of maternal effects on temperature preference in side‐blotched lizards: implications for evolutionary response to climate change

Natural populations respond to selection pressures like increasing local temperatures in many ways, including plasticity and adaptation. To predict the response of ectotherms like lizards to local temperature increase, it is essential to estimate phenotypic variation in and determine the heritability of temperature‐related traits like average field body temperature (T_b) and preferred temperature (T_p). We measured T_p of Uta stansburiana in a laboratory thermal gradient and assessed the contribution of sex, reproductive status and throat color genotype to phenotypic variation in T_b of adult lizards. Females had higher T_p than males. However, they temporarily preferred lower temperature when gravid than when nongravid. Using a nested half‐sib design for genetic crosses in the laboratory, we estimated relative contributions of additive genetic variation and maternal effects to T_p of hatchlings. Our results show that maternal effects, but not additive genetic variation, influence T_p of hatchlings in U. stansburiana. Maternal T_p and the presence or absence of blue throat color alleles significantly influenced T_p of hatchlings. We discuss ecological and evolutionary consequences of these maternal effects in the context of rapid climate change and natural selection that we measure on progeny survival to maturity as a function of maternal T_p.     

The effect of photoperiod on temperature selection in the European green lizard,Lacerta viridis

Summary Voluntary body temperature selection of unrestrained Lacerta viridis revealed consistant photoperiod entrained diel patterns. Each daily cycle was characterized by an elevation in body temperature (T _b) to a high level plateau which declined at the onset of scotophase to a low level; both of which were maintained within narrow ranges.Under natural photoperiod in fall, lizards responded to shorter days by sinking low level T _b's and expanding the duration of these low levels until no rhythmicity was shown. Subsequent exposure to long day, LD 16:8, induced self-arousal and a slightly altered diel T _b selection with significantly higher T _b's being chosen at both the elevated and lower daily levels. Changes in the relations of diel T _b selection due to shift in photoperiod, suggest that photoperiod acts as a seasonal indicator for thermal adaptation.This research was carried out in partial fulfillment of a diploma degree at the J.W.G. University, Frankfurt/Main     

Dietary fats,selected body temperature and tissue fatty acid composition of agamid lizards (Amphibolurus nuchalis)

The composition of tissue and membrane fatty acids in ectothermic vertebrates is influenced by both temperature acclimation and diets. If such change in body lipid composition and thermal physiology were linked, a diet-induced change in body lipid composition should result in a change in thermal physiology. We therefore investigated whether the selected body temperature of the agamid lizardAmphibolurus nuchalis (body mass 20 g) is influenced by the lipid composition of dietary fatty acids and whether diet-induced changes in thermal physiology are correlated with changes in body lipid composition. The selected body temperature in two groups of lizards was indistinguishable before dietary treatments. The selected body temperature in lizards after 3 weeks on a diet rich in saturated fatty acids rose by 2.1 °C (photophase) and 3.3 °C (scotophase), whereas the body temperature of lizards on a diet rich in unsaturated fatty acids fell by 1.5 °C (photophase) and 2.0 °C (scotophase). Significant diet-induced differences were observed in the fatty acid composition of depot fat, liver and muscle. These observations suggest that dietary lipids may influence selection of body temperature in ectotherms via alterations of body lipid composition.Abbreviations bm body mass - FA fatty acid(s) - MUFA monounsaturated fatty acids - PUFA polyunsaturated fatty acids - SFA saturated fatty acids - T _a air temperature - T _b body temperature - UFA unsaturated fatty acids     

The emergence of endothermy in the black-footed and Laysan albatrosses

Eggs with pip-holes of the black-footed (Diomedea nigripes) and Laysan (Diomedea immutabilis) albatrosses were exposed to various air temperatures in the range 20–35°C in order to detect signs of incipient endothermy in late embryos. No evidence of endothermy was found. In contrast, the O₂ consumption of most hatchlings increased in response to cooling, the O₂ consumption at an air temperature of 25° C exceeding that between 34 and 35°C by 40%. In a minority of hatchlings this response was not seen. It was suggested that endothermy may develop at some time during the 24 h after hatching.Abbreviations bm body mass - C _total total thermal conductance of tissues and plumage - f respiratory frequency - FE_{O 2} fractional concentration of oxygen in air leaving chamber - FI_{O 2} fractional concentration of oxygen in air entering chamber - T _a an temperature - T _b deep-body temperature - V air-flow rate - VO₂ oxygen consumption     

Standard operative temperatures and cost of thermoregulation in the arctic ground squirrel,Spermophilus undulatus

Summary Body temperatures (T _b) and daily activity patterns of free-living arctic ground squirrells (Spermophilus undulatus) were determined via telemetry at a field site in northern Alaska. Simultaneous measurements were made of ambient temperature (T _a), wind speed (V), and incident solar radiation. The operative environmental temperature (T _e) for ground squirrels was obtained from fur-covered, thin metal taxidermic models of the animals. Standard operative temperature (T _es), a comparative index of heat flow, was calculated from T _e, V, and laboratory measurements of thermal conductivity.During the period of the study (August), S. undulatus were active for about 14 h per day (06.00 to 20.00 h). T _b was high throughout the daily cycle, averaging 38–39°C. Circadian variations in T _b were slight; average T _b values dropped <1°C at night. Daytime T _b fluctuations were not closely correlated to activity or to changes in environmental conditions. Air temperatures during the study were low, usually between 10 and 15°C during the day. However, T _es in exposed areas was normally higher, even though skies were generally overcast. During periods of sunshine, T _es may be as high as 34°C. The absence of nocturnal activity may result from increased costs of thermoregulation at night, which sharply reduces foraging efficiency. The high and stable body temperatures of S. undulatus probably result from thermoneutral daytime T _es, low activity levels, and the use of well-insulated nests.     

Thermal ecology of the Australian agamid Pogona barbata

This study compares the thermal ecology of male bearded dragon lizards (Pogona barbata) from south-east Queensland across two seasons: summer (1994–1995) and autumn (1995). Seasonal patterns of body temperature (T _b) were explored in terms of changes in the physical properties of the thermal environment and thermoregulatory effort. To quantify thermoregulatory effort, we compared behavioral and physiological variables recorded for observed lizards with those estimated for a thermoconforming lizard. The study lizards' field T _bs varied seasonally (summer: grand daily mean (GDM) 34.6 ± 0.6°C, autumn: GDM 27.5 ± 0.3°C) as did maximum and minimum available operative temperatures (summer: GDM T _max 42.1 ± 1.7°C, T _min 32.2 ± 1.0°C, autumn: GDM T _max 31.7 ± 1.2°C, T _min 26.4 ± 0.5°C). Interestingly, the range of temperatures that lizards selected in a gradient (selected range) did not change seasonally. However, P. barbata thermoregulated more extensively and more accurately in summer than in autumn; lizards generally displayed behaviors affecting heat load nonrandomly in summer and randomly in autumn, leading to the GDM of the mean deviations of lizards' field T _bs from their selected ranges being only 2.1 ± 0.5°C in summer, compared to 4.4 ± 0.5°C in autumn. This seasonal difference was not a consequence of different heat availability in the two seasons, because the seasonally available ranges of operative temperatures rarely precluded lizards from attaining field T _bs within their selected range, should that have been the goal. Rather, thermal microhabitat distribution and social behavior appear to have had an important influence on seasonal levels of thermoregulatory effort. Received: 28 April 1997 / Accepted: 29 December 1997     

Embryonic development rate and hatchling phenotypes in the Chinese three-keeled pond turtle (Chinemys reevesii): The influence of fluctuating temperature versus constant temperature

Although the effects of constant temperatures on hatchling traits have been extensively studied in reptiles, the effects of fluctuating temperatures remain poorly understood. Eggs of the Chinese three-keeled pond turtle (Chinemys reevesii) were incubated at a constant temperatures (28 °C) and two fluctuating temperatures (28±3 °C and 28±6 °C) to test for the influence of thermal environment on incubation duration, hatchling traits, and post-hatching growth. Incubation duration was shorter at constant temperature than at fluctuating temperatures. The sex ratio of hatchlings varied among temperature treatments, with more females from 28±6 °C than from 28 °C. The size and mass were greater for hatchlings from a constant temperature than from fluctuating ones, but this difference in body size disappeared when the hatchlings were 3 months old. In addition, the swimming ability, survival, and growth of hatchlings from fluctuating temperatures did not differ from those of hatchlings from constant temperature, when they were kept at an artificial environment without food scarcity or predation. Therefore, the thermal environments with various temperature fluctuations used in this study do not significantly affect fitness-related hatchling traits in this species.     

Thermal biology,microhabitat selection,and conservation of the insular lizard Podarcis hispanica atrata

Summary We studied aspects of the thermal biology and microhabitat selection of the endangered lizard Podarcis hispanica atrata during autumn in the field and laboratory. Body temperatures (T _b ) of active lizards were within a narrow range, were largely independent of ambient temperatures, and exhibited little diel variation. Activity T _b s largely coincided with the selected temperatures maintained in a laboratory thermogradient and with T _b s that maximize running performance. Alternation of basking with other activities and shuttling between sun and shade were obvious aspects of thermoregulatory behaviour. Lizards shifted microhabitat use throughout the day. During early morning and late afternoon, basking lizards were restricted to rocky sites surrounded by shrubs. Near midday lizards used a wider array of microhabitats, and many moved in open grassy sites. Juveniles maintained lower activity T _b s, had lower selected temperatures, and basked less frequently than the adults. Juveniles occupied open grassy patches more often than the adults. We discuss the relevance of our results for the conservation of this extremely rare lizard and the management of its habitats.     

EVOLUTIONARY PATTERNS OF THE THERMAL SENSITIVITY OF SPRINT SPEED IN ANOLIS LIZARDS

I present evidence that the thermal sensitivity of sprint speed of Anolis lizards has evolved to match the activity body temperatures (T_b) experienced by local populations in nature. Anolis lizards from a range of altitudes in Costa Rica have limited thermoregulatory abilities and consequently have field T_b that differ substantially in median and interquartile distance (a measure of variability). Experimentally determined maximal sprint temperatures (T_b at which lizards run fastest) were positively correlated with median field T_b, and performance breadths (ranges of T_b over which lizards run well) were correlated with the variability (interquartile distance) of field T_b in the species I examined. Such correlations would be expected if the thermal sensitivity of sprint speed and field T_b had evolved together to improve the sprint performance of lizards in nature. Integration of laboratory and field studies indicates that several species of Anolis regularly experience impaired sprint speeds in the field, despite apparent evolutionary modification of their thermal physiologies. However, this impairment would have been more severe if the thermal sensitivities of sprint speed had not evolved. Data from other groups of lizards indicate that the thermal sensitivity of sprint speed has not evolved to match T_b of local populations (Hertz et al., 1983; Crowley, 1985). These lizards experience less variable T_b and less impairment of sprint speeds in the field than do the anoles. Thus, selection for modification of the thermal sensitivity of sprint speed might have been stronger for anoles than for other groups of lizards.     

Seasonal changes in daily metabolic patterns of Lacerta viridis

Summary Lacerta viridis maintained under natural photoperiodic conditions show daily and seasonal changes in metabolic rates and body temperature (T _b) as well as seasonal differences in sensitivity to temperature change. At all times of the year lizards have a daily fluctuation in oxygen consumption, with higher metabolic rates during the light phase of the day when tested at a constant ambient temperature (T _a) of 30°C. Rhythmicity of metabolic rate persists under constant darkness, but there is a decrease in the amplitude of the rhythm.Oxygen consumption measured at various T_as shows significant seasonal differences at T _as above 20°C. Expressed as the Arrhenius activation energy, metabolic sensitivity of Lacerta viridis shows temperature dependence in autumn, which changes to metabolic temperature independence in spring at T _as above 20°C. The results indicate a synergic relationship between changing photoperiod and body temperature selection, resulting in seasonal metabolic adjustment and seasonal adaptation.Abbreviations ANOVA analysis of variance - LD long day (16 h light) - SD short day (8 h light) - T _a ambient temperature - T _b body temperature     

Do temperature fluctuations during incubation always play an important role in shaping the phenotype of hatchling reptiles?

Fluctuating temperatures (FTs) influence hatchling phenotypes differently from constant temperatures (CTs) in some reptiles, but not in others. This inconsistency raises a question of whether thermal fluctuations during incubation always play an important role in shaping the phenotype of hatchlings. To answer this question, we incubated eggs of Naja atra under one CT (28 °C, CT), two temperature-shift [cold first (CF) and hot first (HF) in which eggs were first incubated at 24 or 32 °C and then at the other, each for 20 days, and finally at 28 °C until hatching], and one FT thermal regimes. Female hatchlings were larger in snout–vent length but smaller in tail length, head size than male hatchlings from the same-sized egg; female hatchlings had more ventral scales than did male hatchlings. The FT and HF treatments resulted in shorter incubation lengths. Tail length was greatest in the CT treatment and smallest in the FT treatment, with the CF and HF treatments in between; head width was greater in the CT treatment than in the other three treatments. Other examined hatchling traits did not differ among treatments. The observed morphological modifications cannot be attributed to the effect of thermal fluctuations but to the effect of temperatures close to the upper and lower viable limits for the species. Our results therefore support the hypothesis that hatchling phenotype is not altered by thermal fluctuation in species with no phenotypic response to incubation temperature within some thresholds.     

The variance of incubation temperatures does not affect the phenotype of hatchlings in a colubrid snake, Xenochrophis piscator

It has been documented in some reptiles that fluctuating incubation temperatures influence hatchling traits differently than constant temperatures even when the means are the same between treatments; yet whether the observed effects result from the thermal variance, temperature extremes or both is largely unknown. We incubated eggs of the checkered keelback snake Xenochrophis piscator under one fluctuating (Ft) and three constant (24, 27 and 30 °C) temperatures to examine whether the variance of incubation temperatures plays an important role in influencing the phenotype of hatchlings. The thermal conditions under which eggs were incubated affected a number of hatchling traits (wet mass, SVL, tail length, carcass dry mass, fatbody dry mass and residual yolk dry mass) but not hatching success and the sex ratio of hatchlings. Body sizes were larger in hatchlings from incubation temperatures of 24 and 27 °C compared with the other two treatments. Hatchlings from the four treatments could be divided into two groups: one included hatchlings from the 24 and 27 °C treatments, and the other included hatchlings from the 30 °C and Ft treatments. In the Ft treatment, the thermal variance was not a significant predictor of all examined hatchling traits, and incubation length was not correlated with the thermal variance when holding the thermal mean constant. The results of this study show that the mean rather than the variance of incubation temperatures affects the phenotype of hatchlings.     

Daily and seasonal cycles of body temperature and aspects of heterothermy in the hedgehog Erinaceus europaeus

Summary Intra-abdominal temperature-sensitive radio transmitters were used to collect more than 350 sets of body temperature (T _b ) data from 23 captive adult hedgehogs over a 3-year period. Each data set comprised measurements made every 1/2 h for 24-h periods. Between 20 and 60 such data sets were recorded every calendar month, and a total of 17400 measurements of T _b were collected. The hedgehogs were exposed to natural environmental conditions at 57°N in NE Scotland. Hedgehogs showed seasonal changes in mean daily euthermic T _b ,with a July maximum of 35.9±0.2°C, a September minimum of 34.7±0.9°C, and a marked circadian T _b cycle that correlates closely with photoperiod. Maximal T _b occurred within 2 h of midnight and this pattern of nocturnal maximum and diurnal minimum T _b was most marked between April and September. The circadian T _b cycle was least correlated with photoperiod during winter. Hibernal T _b during winter correlated with ambient temperature (T _a ),it was maximal in September (17.7±1.0°C) and minimal in December (5.2±0.9°C). Apart from the tracking of T _a and T _b during hibernal bouts, with a time-lag of 4–6 h, circadian rhythmicity of hibernal T _b was not evident. However, the T _b of hibernating hedgehogs rose significantly when T _a fell below — 5°C, although the animals did not neccessarily arouse. Although hibernal bouts occurred between September and April, 89.5% of such bouts were recorded between November and February. The mean time of entry into hibernation was 01:45±5.1 h GMT while the mean time of the start of spontaneous arousal from hibernation was 11:53±4.8 h GMT. Therefore, during hibernation hedgehogs were either fully aroused at night, when euthermic hedgehogs have maximalT _b ,or in deep hibernation around midday, when euthermic hedgehogs have minimal T _b .Since wild hedgehogs will feed during spontaneous arousal from hibernation, these timings are probably adaptive, and suggest that entry into, and arousal from, hibernation may be extensions of circadian cyclicity. Spontaneous bouts of transient shallow torpor (TST) were recorded throughout the year, with nearly 80% of observations occurring during August and September, at the start of the hibernal period. TST bouts lasted for 4.9±2.9 h, with T _b falling to 25.8±3.1 °C. Only 20% of TST bouts immediately preceded hibernation and their duration did not correlate with T _a or body mass. TST bouts started at 06:51±4.7 h GMT, significantly later than entry into hibernation, and ended at 13:04±5.4 h GMT. The function of TST bouts is unclear, but they may be preparation for the hibernation season or a further energy conservation strategy. When arousing from hibernation hedgehogs warmed at a rate of 1.9±0.4°C·h^-1, and when entering hibernation cooled at 7.9±1.9°C·h^-1. Warming rates were slightly higher during mid-winter when T _b and body mass were minimal, but cooling rates were 44% higher at the end of the hibernal period compared to the start. Cooling and warming rates were strikingly similar to those measured in hedgehogs at 31°N. These results demonstrate that thermoregulation in the hedgehog is closely regulated and changes on a seasonal basis, in meeting with requirements of surviving food shortages and low temperature during winter.Abbreviations T _a ambient temperature - T _b body temperature - CSD circular standard deviation - SWS slow wave sleep - TST transient shallow torpor