Thermoregulation in Malayan sun bears (Helarctos malayanus) and its consequences for in situ conservation

Thermoregulation in Malayan sun bears is not fully understood. Therefore, in this study the effect of meteorological variables on both behavioural and autonomic thermoregulatory mechanisms in sun bears was examined in order to identify temperature thresholds for the activation of various thermoregulatory mechanisms. Infrared thermography was used to non‒invasively determine body surface temperature (T_S) distribution in relation to ambient temperature (T_A) and to determine the thermoneutral zone (TNZ) of sun bears. Thermographic measurements were performed on 10 adult sun bears at T_A between 5 °C and 30 °C in three European zoos. To assess behaviours that contribute to thermoregulation, nine adult sun bears were observed at T_A ranging from 5 °C to 34 °C by instantaneous scan sampling in 60 s intervals for a total of 787 h. Thermographic measurements revealed that the TNZ of sun bears lies between 24 °C and 28 °C and that heat is equally dissipated over the body surface. Behavioural data showed that behaviours related to thermoregulation occurred in advance of energetically costly autonomic mechanisms, and were highly correlated with T_A and solar radiation. While the temperature threshold for the onset of thermoregulatory behaviours below the TNZ lies around 15 °C, which is well below the lower critical temperature (T_LC) assessed by thermography, the onset for behaviours to prevent overheating occurred at 28 °C, which was closer to the estimated upper critical temperature (T_UC) of sun bears. These findings provide useful data on the thermal requirements of sun bears with respect to the species potential to cope with the effects of climate change and deforestation which are occurring in their natural range. Furthermore, these results may have important implications for the care and welfare of bears in captivity and should be taken into consideration, when designing and managing facilities.     

Quantum Speciation of <Emphasis Type="Italic">Yersinia pestis</Emphasis> Plague Microbe in a Heteroimmune Environment: In the Populations of Hibernating Tarbagan Marmots (<Emphasis Type="Italic">Marmota sibirica</Emphasis>)

This review is devoted to the ecological mechanism for the transformation of the population of the psychrophilic saprozoobiont pseudotuberculosis microbe Yersinia pseudotuberculosis O:1b into the population of the obligate blood plague microbe Yersinia pestis in the host–parasite system of the marmot flea (Marmota sibirica–Oropsylla silantiewi). The correspondence of this mechanism to the evolutionary principle of quantum speciation has been shown. The most significant population–genetic microbial transformations took place in the populations of hibernating marmots. The main factor of rapid speciation was the heterothermic and, accordingly, heteroimmune state of host marmots during hibernation. During winter awakenings, the body temperature of marmots increases in an S-shaped manner from 5 to 37°C within a short period of time (from dozens of minutes to several hours). A drastic acceleration of metabolic and immune processes occurs in the temperature range of 20–30°C. Rapid adaptation to the “explosive” increase in the immune activity of the primary host (tarbagan marmot) during its regular winter awakenings was the essence of the process of Y. pestis speciation.     

Adrenal tyrosine hydroxylase activity in the ground squirrel—effect of cold and arousal from hibernation

1. Tyrosine hydroxylase activity in the adrenals was studied in autumn in three groups of the normothermic ground squirrels (Citellus citellus).2. One group was kept at 20–25°C, the second group was kept over the same period in the cold room at 6–8°C, and the third group was examined immediately after the artificial arousal from the hibernation.3. Tyrosine hydroxylase (TH) activity was higher in the euthermic ground squirrel kept at 6–8°C (in the period prior to hibernation) than in those kept during the same period at 20–25°C (P < 0.01).4. TH activity in the adrenals examined immediately after an artificial arousal from the hibernation was lower than in active ones kept at the same environmental temperature (P < 0.01).     

Yellow-bellied marmots do not compensate for a late start: the role of maternal allocation in shaping life-history trajectories

Yellow-bellied marmots, Marmota flaviventris, are obligate hibernators with a relatively short active season. Animals born earlier in the season have higher chances of fulfilling the energetic requirements to survive the long winter. Therefore, the onset of breeding should have a profound impact on juvenile survival. However, there are different ways to compensate for a late start. Late breeders might allocate more resources to late born offspring, making up for the bad start, or juveniles might show compensatory growth. They are not exclusive hypotheses and both can lead to juveniles entering hibernation with a similar body condition. We used data from a long term study in and around the Rocky Mountain Biological Laboratory in Colorado to test these two hypotheses. Animals are individually marked and trapped regularly. We compared mass at weaning, mass at the end of the season, growth rates and survival between animals born earlier and later in the season. We found no evidence of increased maternal input: late breeders had lighter offspring at weaning than early breeders, and late born juveniles did not increase their growth rates. Therefore, late born individuals ended the season with lower body mass, and were thus, less likely to survive the winter. In conclusion, life-history trajectories of juvenile yellow-bellied marmots were determined by maternal allocation, whereas post-weaning decisions did not modify their fate.     

Regulation of the α-ketoglutarate dehydrogenasecomplex during hibernation in a small mammal,the Richardson's ground squirrel (Urocitellus richardsonii)

The citric acid cycle (CAC) is a central metabolic pathway that links carbohydrate, lipid, and amino acid metabolism in the mitochondria and, hence, is a crucial target for metabolic regulation. The α-ketoglutarate dehydrogenase complex (KGDC) is the rate-limiting step of the CAC, the three enzymes of the complex catalyzing the transformation of α-ketoglutarate to succinyl-CoA with the release of CO₂ and reduction of NAD to NADH. During hibernation, the metabolic rate of small mammals is suppressed, in part due to reduced body temperature but also active controls that suppress aerobic metabolism. The present study examined KGDC regulation during hibernation in skeletal muscle of the Richardson's ground squirrel (Urocitellus richardsonii). The KGDC was partially purified from skeletal muscle of euthermic and hibernating ground squirrels and kinetic properties were evaluated at 5°, 22°, and 37 °C. KGDC from hibernator muscle at all temperatures compared with euthermic controls exhibited a decreased affinity for CoA as well as reduced activation by Ca²⁺ ions at 5 °C from both euthermic and hibernating conditions. Co-immunoprecipitation was employed to isolate the E1, E2 and E3 enzymes of the complex (OGDH, DLST, DLD) to allow immunoblot analysis of post-translational modifications (PTMs) of each enzyme. The results showed elevated phospho-tyrosine content on all three enzymes during hibernation as well as increased ADP-ribosylation and succinylation of hibernator OGDH. Taken together these results show that the KGDC is regulated by posttranslational modifications and temperature effects to reorganize enzyme activity and mitochondrial function to aid suppression of mitochondrial activity during hibernation.     

Diet-independent remodeling of cellular membranes precedes seasonally changing body temperature in a hibernator

Polyunsaturated fatty acids (PUFA) have a multitude of health effects. Their incorporation into membrane phospholipids (PL) is generally believed to depend directly on dietary influx. PL influence transmembrane protein activity and thus can compensate temperature effects; e.g. PL n-6 PUFA are thought to stabilize heart function at low body temperature (T(b)), whereas long chain (>C18) n-3 PUFA may boost oxidative capacity. We found substantial remodeling of membranes in free-living alpine marmots which was largely independent of direct dietary supply. Organ PL n-6 PUFA and n-6 to n-3 ratios were highest at onset and end of hibernation after rapid increases during a brief transitional period prior to hibernation. In contrast, longer chain PL n-3 PUFA content was low at end of summer but maximal at end of hibernation. After termination of hibernation in spring, these changes in PL composition were rapidly reversed. Our results demonstrate selective trafficking of PUFA within the body, probably governed by a circannual endogenous rhythm, as hibernating marmots were in winter burrows isolated for seven months from food and external cues signaling the approaching spring. High concentrations of PL n-6 PUFA throughout hibernation are in line with their hypothesized function of boosting SERCA 2a activity at low T(b). Furthermore, we found increasing rate of rewarming from torpor during winter indicating increasing oxidative capacity that could be explained by the accumulation of long-chain PL n-3 PUFA. It may serve to minimize the time necessary for rewarming despite the increasing temperature range to be covered, because rewarming is a period of highest metabolic rate and hence production of reactive oxygen species. Considering the importance of PUFA for health our results may have important biomedical implications, as seasonal changes of T(b) and associated remodeling of membranes are not restricted to hibernators but presumably common among endothermic organisms.     

Thermal comfort of sows in free-range system in Brazilian Savanna

The aim of this work was to evaluate the thermal comfort of sows in a free-range system in the Brazilian Savanna, based on behavior observation, availability of shading resources, meteorological and physiological variables. The sows were analyzed in the gestation sector at Água Limpa Farm from University of Brasília; the sows were housed in paddocks of 1000 m² each containing artificial and natural shading structures, where air temperature (T_air, °C), wind speed, relative humidity (R_H, %) and black globe temperatures (T_G, °C) were collected for the environment characterization in 20-min-intervals. From the black globe temperature, the Mean Radiant Temperature (T_MR, °C) and the Radiant Heat Load (R_HL, W m⁻²) were calculated in the sun and under the shade structures. The total short-wave irradiance was calculated through the sum of direct, diffuse and reflected radiations. For the behavioral evaluation, an ethogram was elaborated, taking in consideration where the animals were in the paddocks, body posture, and the activity performed. The physiological variables such as respiratory rate (breaths.min⁻¹), surface and rectal temperatures (°C) were measured during the experiment. The data was statistically analyzed through analysis of variance and frequency analysis. There was a difference at 11a.m., 2 and 3p.m., with values above 40 °C under the shade and above 70 °C in the sun for the T_MR. The preferential choice was for natural shading by the sows, due to the lower T_MR and R_HL throughout the day and resting activity had been predominated. The rectal temperature did not differ between the animals and the days evaluated, respiratory rate varied according to air temperature, and surface temperature only among the evaluated animals. It was concluded that even when there is a greater radiation incidence and meteorological variables above the condition of comfort for sows, they did not express any abnormal behavior that could indicate discomfort.     

Measurements of secondary neutrons from cosmic radiation with a Bonner sphere spectrometer at 79°N

Air crew members and airline passengers are continuously exposed to cosmic radiation during their flights. Particles ejected by the sun during so-called solar particle events (SPEs) in periods of high solar activity can contribute to this exposure. In rare cases the dose from a single SPE might even exceed the annual dose limit of 1 mSv above which dose monitoring of air crews is legally required in Germany. Measurements performed by means of neutron monitors have already shown that the relative intensity of secondary neutrons from cosmic radiation is enhanced during an SPE, particularly at regions close to the magnetic poles of the Earth where shielding of the cosmic radiation by the geomagnetic field is low. Here we describe a Bonner sphere spectrometer installed at the Koldewey station at 79°N, i.e. about 1,000 km from the geographic North pole, which is designed to provide first experimental data on the time-dependent energy spectrum of neutrons produced in the atmosphere during an SPE. This will be important to calculate doses from these neutrons to air crew members. The system is described in detail and first results are shown that were obtained during quiet periods of sun activity.     

Dynamics of seasonal growth in a long-lived southern hemisphere conifer are linked to early season temperature

Standard correlation approaches in dendroclimatology provide limited scope to elucidate differences between years in timing of growth initiation and cessation. In the Southern Hemisphere (SH), with relatively few long-term climate reconstructions, a clearer understanding of signals contained in ring width variation is of particular importance. In this study, we monitored growth in detail at two sites (low and high altitude) in Lagarostrobos franklinii (Huon pine) for five growing seasons. In concert, local environmental data were recorded, and cambial samples taken on several occasions. Season duration in Huon pine at low altitude lasted about six months, generally starting in September/October and ending in April. At higher altitude, season duration did not exceed about four months and generally started during November, ending in March. The shortest season and smallest rings were linked to cooler conditions compared to other years. On the other hand, an earlier growth onset in the 2011 growing season was evidently brought on by unusually warm conditions in late winter. Growth onset was linked to a running mean temperature of about 8.5 °C and 6.5 °C at the lower and higher altitude sites, respectively. While effects of limiting water on growth cessation were not universally clear, our results suggest that limiting water (during hotter, drier summers) may reduce growth rates, and precipitate earlier growth cessation.     

Seasonal variation in daily activity patterns of free-ranging European ground squirrels (Spermophilus citellus)

Daily aboveground activity of European ground squirrels (Spermophilus citellus) in their natural habitat was recorded with a visual scanning procedure during the active seasons of 1992 and 1993. Activity patterns were analyzed with respect to time of year and to the animal's reproductive state. Aboveground activity started on average 3.9 h (SD 0.6 h, n = 37 days) after civil twilight at dawn and ended on average 3.2 h (SD 0.9 h, n = 37 days) before civil twilight at dusk. Between onset and offset of activity, 54% was spent aboveground, of which 73% was spent foraging. Activity patterns were influenced by photoperiod, rainfall, and by reproductive state. During mating, reproductively active males started activity earlier than females and reproductively inactive males. For females, time spent foraging was high during lactation. The midpoint of daily activity was at 12:16 h (SD 0.37 h, n = 37 days). Activity patterns of European ground squirrels thus appear robustly positioned in the middle of the photoperiod.     

Thermoregulation in free-ranging Nycteris thebaica (Nycteridae) during winter: No evidence of torpor

Bats are among the most heterothermic mammals, with nearly all species investigated under free-ranging conditions to date exhibiting some degree of daily torpor and/or hibernation. We investigated thermoregulation during late winter by seven Nycteris thebaica in a warm, semi-arid habitat in northern South Africa, using temperature-sensitive transmitters to measure skin temperature (T_skin). Unexpectedly, we found no evidence for any expression of daily torpor or hibernation based on a total of 86 days of data from 7 bats (one male and six females), despite air temperatures as low as ～10 °C. Instead, daytime T_skin was distributed unimodally with most values in the 33–35 °C range, and a minimum T_skin of 28.4 °C at a roost temperature of 24.6 °C. There are several possible reasons why N. thebaica may avoid torpor, including predation in roosts, and the long nightly foraging periods of this species compared to many others.     

Social thermoregulation during hibernation in alpine marmots (Marmota marmota)

Summary Body temperature (T _b) of socially hibernating alpine marmots, a pair and two family groups, was monitored continuously from October to March with implanted temperature-sensitive radiotransmitters. At the same time, the animals' behaviour was observed. The recurrent entrances into and arousals from hibernation were highly synchronised within groups. Group members always lay huddled together when euthermic and also when torpid with a few exceptions at higher ambient temperatures (T _a). Body contact with euthermic nestmates warmed torpid marmots passively. TheT _b of animals reentering hibernation did not fall to values close toT _a as long as euthermic group members were present. Although animals presumably save energy through social thermoregulation, especially when euthermic, these benefits are not necessarily mutual among group members. Differences in thermoregulatory behaviour of individuals described in this study could be responsible for differential weight losses during winter as found in the natural habitat (Arnold 1986).     

Impact of cofactor-binding loop mutations on thermotolerance and activity of E. coli transketolase

Improvement of thermostability in engineered enzymes can allow biocatalysis on substrates with poor aqueous solubility. Denaturation of the cofactor-binding loops of Escherichia coli transketolase (TK) was previously linked to the loss of enzyme activity under conditions of high pH or urea. Incubation at temperatures just below the thermal melting transition, above which the protein aggregates, was also found to anneal the enzyme to give an increased specific activity. The potential role of cofactor-binding loop instability in this process remained unclear. In this work, the two cofactor-binding loops (residues 185–192 and 382–392) were progressively mutated towards the equivalent sequence from the thermostable Thermus thermophilus TK and variants assessed for their impact on both thermostability and activity. Cofactor-binding loop 2 variants had detrimental effects on specific activity at elevated temperatures, whereas the H192P mutation in cofactor-binding loop 1 resulted in a two-fold improved stability to inactivation at elevated temperatures, and increased the critical onset temperature for aggregation. The specific activity of H192P was 3-fold and 19-fold higher than that for wild-type at 60 °C and 65 °C respectively, and also remained 2.7-4 fold higher after re-cooling from pre-incubations at either 55 °C or 60 °C for 1 h. Interestingly, H192P was also 2-times more active than wild-type TK at 25 °C. Optimal activity was achieved at 60 °C for H192P compared to 55 °C for wild type. These results show that cofactor-binding loop 1, plays a pivotal role in partial denaturation and aggregation at elevated temperatures. Furthermore, a single rigidifying mutation within this loop can significantly improve the enzyme specific activity, as well as the stability to thermal denaturation and aggregation, to give an increased temperature optimum for activity.     

Thermoregulatory responses to temperature manipulation of the spinal cord in the marmot

Yellow-bellied marmots (M. flaviventris) acclimated to T_a = 20 °C were implanted with U-shaped polyethylene thermodes in the peridural space of the spinal cord. Decreasing the temperature of the cervical, thoracic, or lumbar areas of the cord increased heart rate, electromyographic activity, and oxygen consumption in the animals. These responses differed qualitatively from those elicited by heating the same cord areas, indicating specificity of the response to the temperature change.Increases in heat production were proportional to the amount of cooling of the cord. The thoracic area was found to be more thermosensitive than the lumbar area. No behavioral or physical thermoregulation was apparent when the spinal cord temperature was changed in these animals.In addition to the conclusion that regulation of spinal cord temperature may be important in the euthermic marmot, it was postulated that the temperature receptors located in the thoracic cord of the marmot may be important in maintaining shivering thermogenesis during arousal from hibernation.     

Predicting military working dog core temperature during exertional heat strain: Validation of a Canine Thermal Model

Military working dogs (MWDs) operate under a wide range of conditions, including hot environments. Predicting how long a MWD can safely work without overheating is important for both health and performance. A Canine Thermal Model (CTM) was developed to predict core temperature (Tc) of MWDs. The CTM calculates heat storage from the balance of heat production from metabolism and heat exchange with the environment. Inputs to the CTM are: meteorological conditions (ambient temperature, relative humidity, solar radiation and wind speed), physical characteristics of the dog (mass, length), and metabolic activity (MET level, estimated from accelerometer data). The CTM was validated against Tc measured in 23 MWDs during training sessions (11.6 ± 5.0 min (mean ± standard deviation), range 4–26 min) in October (24 °C, 52% RH), March (14 °C, 74% RH), or August (28 °C, 64% RH), and 24 kennel MWDs during a standard exercise walk (11.4 ± 3.3 min, range 5.6–18 min) in July (26 °C, 77% RH). The CTM was considered acceptable if predicted Tc was within ±0.5 °C of measured Tc at the end of exercise. Compared to Tc at the end of training sessions (39.8 ± 0.6 °C, range 38.4–41.1 °C) and exercise walks (40.0 ± 0.7 °C, range 38.9–41.4 °C), the CTM-predicted Tc was within ±0.5 °C for 71 of 84 cases (85%) and 19 of 24 cases (79%), respectively. The mean difference between CTM-predicted and measured final Tc during training was -0.04 ± 0.43 °C, with 80 of 84 cases (95%) within the range of ±2 SD (Bland Altman comparison). During exercise walks the mean difference was -0.15 °C ± 0.57, with 23 of 24 cases (96%) within ±2 SD. These results support the use of the CTM to predict Tc of MWDs for the types of physical activities described above.     

Temperature and altitude modulate feeding attributes of Mexican beetle,Zygogramma bicolorata Pallister on Parthenium hysterophorus

Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) is an effective biocontrol agent of Parthenium hysterophorus L. which is an alien invasive herbaceous weed with a pan-tropical distribution. The present study aimed to assess the effects of temperature and altitude on feeding attributes (consumption rate, conversion efficiency and growth rate) of adults from the wild populations of Z. bicolorata inhabiting India and Nepal. Results revealed that adults inhabiting areas of low temperature (24°C ‒ 25°C) and high altitude (415 m ‒1400 m) were large and had higher food consumption rates. In contrast, those inhabiting areas of high temperature (34°C ‒ 36°C) and low altitude (81 m ‒ 229 m) were smaller and had higher food utilization efficiencies. In all the eco-climatic regions, females were larger than males and had higher feeding attributes than their counterparts. Temperature between 27°C and 30°C was found optimal for Z. bicolorata adults to convert and utilize the food biomass to body mass. Above the optimal temperature the feeding attributes decreased. Present results suggest that there exists a possibility for decrease in body size, and thereby weed biocontrol efficiency of Z. bicolorata adults with an increase in temperature due to global climate change.     

Deletion and site-directed mutagenesis of laccase from Shigella dysenteriae results in enhanced enzymatic activity and thermostability

A putative laccase gene was cloned from Shigella dysenteriae W202 and expressed in Escherichia coli as a soluble fusion protein with high yield. The purified product (Wlac) was characterized as the CueO-like laccase from E. coli, a monomer of molecular mass 55 kDa, with a maximum activity of 24.4 U/mg (K_m = 0.086) and a pH optimum of 2.5, in a standard assay using ABTS (2,2′-azino-di(3-ethyl-benzthiazoline-6-sulfonate) as the substrate. Activity was stable at 0–25 °C but inhibited above 40 °C. Purified Wlac was completely inhibited by 200 mM EDTA and partially by 32 mM SDS, 50 mM NaN₃ and 60 mM thioglycolic acid. Activity was stimulated by Cu²⁺; other metal ions had only slight or negative effects. Two mutated variants, WlacS and WlacD, were obtained by substituting Glu 106 with Phe 106, and adding a deletion of an α-helix domain (from Leu 351 to Gly 378). WlacS had a 2.2-fold (52.9 U/mg) and WlacD a 3.5-fold (85.1 U/mg) higher enzyme activity than the wild-type laccase and WlacD showed greater thermostability at higher temperatures. Sce VMA intein-associated fusion proteins maintained ～80% of total enzyme activity. Thus, deletion and site-directed mutagenesis of laccases are capable of promoting both enzymatic activity and thermostability.     

Influence of night length on home range size in the northern bat Eptesicus nilssonii

The northern bat Eptesicus nilssonii is widespread in Fennoscandia, with breeding populations well above the Arctic Circle. I studied this species at its extreme northern limit, at 69°N in Norway. I radio-tracked 17 bats from 2 maternity roosts during 2003–2006 to study the influence of the midnight sun and increasing lengths of darkness on activity (time spent out of roost) and home range size. Activity and home range was highly correlated with night length (light intensity); both increasing progressively with season. Bats were classified into 3 groups based on the time of the season they were tracked (basically July, August and September–October); short activity (average 1.57 h) and small home range (average 0.91 km²), medium activity (3.69 h) and medium-sized home range (4.58 km²), and long activity (4.80 h) and large home range (17.2 km²). Bats visited roosts several times during the night, and the duration of roost visits increased significantly by group. The number of periods out of roost increased from the first to the second group (1.45 vs. 2.36 flight periods per night), but insignificantly to the third group (2.37 flights). The most significant increase in activity and home range was associated with the first flight of juveniles in early August. These bats appeared to have a threshold level of around 1700 lux for activity out of roost, with little difference between light levels at emergence and return (the second group returned in significantly poorer light than they emerged in). Although the northern bat at this extreme latitude had adapted to the ambient light conditions, the bright nights under the midnight sun and the short season strongly reduced their window of opportunity for activity and may possibly reduce survival and reproductive success.     

Rotator cuff tendinopathy alters the muscle activity onset and kinematics of scapula

Athletes with rotator cuff (RC) tendinopathy demonstrate an aberrant pattern of scapular motion which might relate to deficits in the scapular muscles. This study aimed to determine whether alteration in scapular kinematics is associated with deficits in the activity onset of scapular muscles. Forty-three male volleyball players (17 asymptomatic and 26 with RC tendinopathy) joined the study. Three-dimensional scapular kinematics was quantified using an acromial marker cluster method. The activity onset of the upper (UT), middle (MT), and lower trapezius (LT), and serratus anterior (SA) during arm abduction was assessed with electromyography. Athletes with RC tendinopathy demonstrated less scapular upward rotation (6.6 ± 2.3 vs. 8.2 ± 1.1°, p = 0.021) in the early phase of shoulder abduction from 0° to 30° when compared to asymptomatic athletes. The tendinopathy group had delayed activity onset of LT (14.1 ± 31.4 ms vs. 74.4 ± 45.1 ms, p < 0.001) and SA (−44.9 ± 26.0 ms vs. 23.0 ± 25.2 ms, p < 0.001) relative to UT when compared to the asymptomatic group. In asymptomatic athletes, earlier activity onset of MT and LT relative to UT was associated with more scapular upward rotation during 0–30° of abduction (r = 0.665, p = 0.021) and 30–60° of abduction (r = 0.680, p = 0.015), respectively. Our findings showed the control of the scapular upward rotation is related to the activity onset of the scapular muscles in athletes.     

Thermoregulation as a limit to habitat use in alpine marmots (Marmota marmota)

Summary The body temperature (T _b) of free-living alpine marmots rose with activity; the higher the effective environmental temperature (T _e), the higher the rise. Maximum T _bof 40° C was reached at the time of greatest activity in late afternoon or evening. The activity pattern was strongly influenced by the microclimate. Up to an T _eof 25° C the animals spent more time above ground and were more active the higher T _ewas, but above 25° C this trend was reversed, and the animals withdrew increasingly into their burrows. On warm days the activity pattern was therefore bimodal and above ground presence was reduced, in contrast to cool days. Hence behavioural thermoregulation limits the available time for above ground activity on days with high T _ein this strictly diurnal species. We suggest that the alpine marmots' preference for south oriented slopes is due to the better conditions for hibernation there, the microclimate during summer is more favourable on northerly slopes. Thermoregulatory constraints could also keep alpine marmots away from lower elevations.