Rates Of Evaporative Water Loss Research Articles

Metabolic ecology of cockatoos in the south-west of Western Australia

This study examined the metabolic ecology of six cockatoo taxa endemic to the south-west of Western Australia. As the availability of food is one factor that may influence the abundance and distribution of these cockatoos, we document here their baseline energy requirements and feeding patterns. Evaporative waterloss was also measured as this may correlate with the aridity of the species’ environment. Basal metabolic rate was significantly lower at 0.62 ± 0.13 mL O2 g–1 h–1 for the inland red-tailed black cockatoo than 1.11 ± 0.16 mL O2 g–1 h–1 for the forest red-tailed black cockatoo, but there was no significant difference in metabolic rate between the two white-tailed black cockatoos (0.86 ± 0.18 for Carnaby’s and 0.81 ± 0.11 mL O2 g–1 h–1 for Baudin’s) or the two corellas (0.95 ± 0.12 for Butler’s and 0.70 ± 0.04 mL O2 g–1 h–1 for Muir’s). There were no significant differences between the two white-tailed black cockatoos, and between the two corellas, with respect to evaporative water loss. The inland red-tailed black cockatoo had a significantly lower rate of evaporative water loss (0.44 ± 0.07 mg g–1 h–1) than the forest red-tailed black cockatoo (0.70 ± 0.06 mg g–1 h–1), which is presumably an adaptation to its more arid habitat. The total energy content of assorted native and introduced food items that form significant proportions of the diets for these cockatoos varied from only 0.17 kJ for a 9-mg Emex australis seed to 63.9 kJ for a 3-g Banksia attenuata nut. The energy content of each food item and the estimated daily energy requirements of the cockatoos enabled the calculation of the numbers of nuts/cones/seeds required by each species for a day, which ranged from 11 B. attenuata nuts for a Carnaby’s cockatoo to 3592 Persoonia longifolia seeds for a forest red-tailed black cockatoo.

Cold-hardiness and evaporative water loss in hatchling turtles.

North American turtles hatch in late summer and spend their first winter either on land or underwater. Adaptations for terrestrial overwintering of hatchlings in northern regions, where winter thermal and hydric regimes are harsh, have not been systematically investigated in many species. We measured intrinsic supercooling capacity, resistance to inoculative freezing, and desiccation resistance in hatchlings of terrestrial and aquatic turtles collected from northern (Terrapene ornata, Chrysemys picta bellii, Kinosternon flavescens, Chelydra serpentina) and southern (Chrysemys picta dorsalis, Trachemys scripta, Sternotherus odoratus, Sternotherus carinatus) locales. Supercooling capacity was estimated from the crystallization temperature of turtles cooled in the absence of external ice nuclei. Mean values ranged from -8.1 degrees to -15.5 degrees C and tended to be lower in terrestrial hibernators. Inoculation resistance was estimated from the crystallization temperature of turtles cooled in a matrix of frozen soil. These values (range of means: -0.8 degrees to -13.6 degrees C) also tended to be lower in the terrestrial hibernators, especially C. picta bellii. Mean rates of evaporative water loss varied markedly among the species (0.9-11.4 mg g(-1) d(-1)) and were lowest in the terrestrial hibernators. Most species tolerated the loss of a modest amount of body water, although half of the sample of S. carinatus died from desiccation. In general, turtles did not regain lost body water from wet soil, and immersion in free water was required for rehydration. Therefore, desiccation resistance may be an important adaptation to terrestrial hibernation. Resistances to inoculative freezing and desiccation were directly correlated, perhaps because they are governed by the same morphological characteristics.

Effects of Ozone on Evaporative Water Loss and Thermoregulatory Behavior of Marine Toads (Bufo marinus)

Ozone (O3) is a strong pulmonary irritant and causes a suite of respiratory tract inflammatory responses in humans and other mammals. In addition to lung injury, rodents exposed to O3 exhibit a pronounced decrease in core body temperature at rest, which may offer a protective effect against O3 damage. The effects of O3 on other vertebrates have not been studied. Compared to individuals exposed to air (N=34), Bufo marinus toads exposed to O3 (N=32) for 4 h lost 3.78 g body mass (adjusted mean from analysis of covariance, body mass mean±SD, 90.1±21.90 g). We tested the thermoregulatory responses of 22 toads in a thermal gradient 1, 24, and 48 h after 4-h exposure to air (N=11) or 0.8 ppm O3 (N=11). Individual toad thermal preferences were also significantly repeatable across all trials (intraclass correlation=0.66, P <0.001). We did not observe a direct effect of O3 exposure on the preferred body temperatures (PBT) of toads. However, O3 exposure did have an indirect effect on selected temperatures. Ozone-exposed toads with higher evaporative water loss rates, in turn, also selected lower PBT, voluntary minimum, and voluntary maximum temperatures 24 h post-exposure. Ozone exposure may thus alter both water balance and thermal preferences in anuran amphibians.

Rates of Water Loss and Estimates of Survival Time under Varying Humidity in Juvenile Snapping Turtles (Chelydra serpentina)

Juvenile snapping turtles may be highly susceptible to dehydration during overland movement because of their aquatic nature and large surface area to volume ratio. The present study examined the influence of body size and relative humidity on rates of evaporative water loss and estimates of survival time. Larger hatchlings had higher rates of evaporative water loss but longer survival times resulting from their greater absolute water contents. Rates of evaporative water loss decreased, and estimated survival times increased with increasing relative humidity. The findings suggest that evaporative water loss may be an important factor influencing survivorship and behavior during overland movements of juvenile snapping turtles.

Airway surface liquid osmolality measured using fluorophore-encapsulated liposomes.

The airway surface liquid (ASL) is the thin layer of fluid coating the luminal surface of airway epithelial cells at an air interface. Its composition and osmolality are thought to be important in normal airway physiology and in airway diseases such as asthma and cystic fibrosis. The determinants of ASL osmolality include epithelial cell solute and water transport properties, evaporative water loss, and the composition of secreted fluids. We developed a noninvasive approach to measure ASL osmolality using osmotically sensitive 400-nm-diam liposomes composed of phosphatidylcholine/cholesterol/polyethylene glycol-phosphatidylcholine (1:0.3:0.08 molar ratio). Calcein was encapsulated in the liposomes at self-quenching concentrations (30 mM) as a volume-sensitive marker, together with sulforhodamine 101 (2 mM) as a volume-insensitive reference. Liposome calcein/sulforhodamine 101 fluorescence ratios responded rapidly (< 0.2 s) and stably to changes in solution osmolality. ASL osmolality was determined from calcein/sulforhodamine 101 fluorescence ratios after addition of microliter quantities of liposome suspensions to the ASL. In bovine airway epithelial cells cultured on porous supports at an air-liquid interface, ASL thickness (by confocal microscopy) was 22 microm and osmolality was 325 +/- 12 mOsm. In anesthetized mice in which a transparent window was created in the trachea, ASL thickness was 55 microm and osmolality was 330 +/- 36 mOsm. ASL osmolality was not affected by pharmacological inhibition of CFTR in airway cell cultures or by genetic deletion of CFTR in knockout mice. ASL osmolality could be increased substantially to > 400 mOsm by exposure of the epithelium to dry air; the data were modeled mathematically using measured rates of osmosis and evaporative water loss. These results establish a ratio imaging method to map osmolality in biological compartments. ASL fluid is approximately isosmolar under normal physiological conditions, but can become hyperosmolar when exposed to dry air, which may induce cough and airway reactivity in some patients.

Energy expenditure and water flux of free‐living Dune Larks in the Namib: a test of the reallocation hypothesis on a desert bird

Abstract1. Dune Larks (Mirafra erythroclamys) are the only avian species that has evolved the capability of surviving in the Namib Sand Sea, one of the driest regions in the world. Their field metabolic rate (FMR) and water flux, as measured by doubly labelled water, during the breeding and non‐breeding season are reported here.2. FMR is relatively constant over the annual cycle, which conforms to the ‘reallocation hypothesis’. With data pooled for both seasons, males expended energy at a rate of 97·5 ± 20·4 kJ day−1 (±1 SD) and females at 87·5 ± 13·0 kJ day−1. The data supported the hypothesis that Dune Larks do not possess a reduced FMR, a result attributable to their elevated basal metabolism. In a previous laboratory investigation, Dune Larks had a low rate of evaporative water loss despite their elevated basal metabolic rate (BMR). The present study demonstrated that this low evaporative water loss translates into a low water influx in the field.3. The FMR of Dune Lark females equalled 88·1 ± 6·9 kJ day−1 during incubation, and 88·5 ± 9·9 kJ day−1 when they were feeding 8–10‐day‐old nestlings. These data do not support the idea that the incubation period is a time of low energy demand.4. Dune Larks had a relatively constant water influx throughout the year. For sexes combined, mass‐adjusted values of water influx averaged 0·59 ml H2O/(day mass0·682).5. Calculations showed that neonates received 10 kJ day−1 whereas towards the end of the nestling period, chicks were fed 75 kJ day−1, the maximum gross energy intake for nestlings. During chick rearing, males increased the amount of food that they found by 57·7%, females by 64·3%, late in the nestling period.6. Dune Larks foraged in the morning and late afternoon, but were constrained by their environment to seek shade at midday during the breeding season.7. Metabolic water production plays a significant role in the water economy of Dune Larks. Assuming a mixed diet, 47% of their water intake comes from the oxidation of food stuffs.

The beneficial acclimation hypothesis versus acclimation of specific traits: physiological change in water-stressed Manduca sexta caterpillars.

Do organisms make beneficial physiological adjustments in response to environmental change? We examined this question by measuring the effects of short-term (12-36 h) and long-term (larval lifetime) hydric stress on the tobacco hornworm, Manduca sexta. Larvae were reared from the first instar on low-water (69%) or high-water (80%) artificial diets and then transferred early in the fifth instar to the same or opposite diet (2x2 design). Within the subsequent 36 h, we measured 24-h growth rates and three primary determinants of the water budget: water gain via consumption and water loss via evaporation and defecation. Larvae preexposed to low-water diet grew less rapidly on low-water diet than those switched acutely to low-water diet from high-water diet, showing that larvae preexposed to a particular environment do not necessarily acclimate beneficially to that environment. Our data on water fluxes to and from larvae, however, strongly suggest that water-stressed larvae did make beneficial physiological adjustments. Larvae responded to short-term hydric stress by minimizing rates of water excretion, primarily by increasing rates of rectal water absorption. Larvae responded to chronic water stress by significantly reducing rates of evaporative water loss; they also showed additional reductions in fecal water excretion, but these decreases were due to lowered consumption and not to further increases in rate of rectal water absorption. This mismatch between maladaptive acclimation of organismal performance and beneficial adjustment of suborganismal traits can be reconciled by recognizing that organismal physiology is hierarchical: fitness-related performance traits represent the aggregate outcome of numerous, more mechanistic physiological traits. Although chronic exposure to an environment may depress the aggregate effect of these mechanistic traits on performance, organisms are not precluded from making beneficial adjustments to individual traits contributing to performance.

Intraspecific physiological variability of the gastropod Littorina saxatilis related to the vertical shore gradient in the White and North Seas

Physiological responses to desiccation and temperature stress as well as behavioural responses to fast and abrupt environmental changes were investigated in high- and low-shore Littorina saxatilis (Olivi) from several populations from the White and North Seas. Variations in evaporation rates, resistance to air exposure and to acute and chronic temperature stress between animals from different shore levels were similar in White and North Sea periwinkles, consistent with the adaptive nature of these variations. High-shore snails were found to be able to conserve body water reserves better, to resist higher temperatures and to survive longer under conditions of combined temperature and desiccation stress than their low-shore counterparts. In a temperature range of 25 to 35 °C, the rate of evaporative water loss was positively correlated with temperature in low-shore snails while being largely temperature-independent in high-shore snails. Median lethal time during air exposure in L. saxatilis was negatively but not linearly related to the temperature of exposure. In a temperature range of 30 to 38 °C, the resistance to heat exposure in air was only slightly dependent on the temperature, with Q 10 = 1.4 for the median lethal time; the heat resistance dropped drastically at temperatures above 38 °C, with Q 10 = 593.8. This suggests different mechanisms of temperature resistance in different parts of the studied temperature range. In contrast, behavioural response to extreme salinity fluctuations was not uniform in the high- and low-shore periwinkles from the White and North Seas, which may reflect specific environmental conditions at different shore levels in the two areas studied. Observed physiological and behavioural variations are discussed from the viewpoint of different adaptive strategies employed by eulittoral and eulittoral-fringe animals within populations of a single species.

Nasal respiratory turbinate function in birds.

Nasal respiratory turbinates are complex, epithelially lined structures in nearly all birds and mammals that act as intermittent countercurrent heat exchangers during routine lung ventilation. This study examined avian respiratory turbinate function in five large bird species (115-1,900 g) inhabiting mesic temperate climates. Evaporative water loss and oxygen consumption rates of birds breathing normally (nasopharyngeal breathing) and with nasal turbinates experimentally bypassed (oropharyngeal breathing) were measured. Water and heat loss rates were calculated from lung tidal volumes and nasal and oropharyngeal exhaled air temperatures (T(ex)). Resulting data indicate that respiratory turbinates are equally adaptive across a range of avian orders, regardless of environment, by conserving significant fractions of the daily water and heat budget. Nasal T(ex) of birds was compared to that of lizards, which lack respiratory turbinates. The comparatively high nasal T(ex) of the lizards in similar ambient conditions suggests that their relatively low metabolic rates and correspondingly reduced lung ventilation rates may have constrained selection on similar respiratory adaptations.

The adjustment of avian metabolic rates and water fluxes to desert environments.

We tested the hypothesis that birds in arid environments, where primary productivity is low and surface water is scarce, have reduced energy expenditure and water loss compared with their mesic counterparts. Using both conventional least squares regression and regression based on phylogenetically independent contrasts, we showed that birds from desert habitats have reduced basal and field metabolic rates compared with species from mesic areas. Previous work showed that desert birds have reduced rates of total evaporative water loss when exposed to moderate environmental temperatures in the laboratory. We tested whether reduced rates of total evaporative water loss translate into low field water fluxes. Conventional ANCOVA indicated that desert birds have reduced water fluxes, but an analysis based on phylogenetically independent contrasts did not support this finding, despite the wide array of taxonomic affiliations of species in the data set. We conclude that the high ambient temperatures, the low primary productivity, and the water scarcity in desert environments have selected for or resulted in reduced rates of energy expenditure and evaporative water loss in birds that live in these climes.

Prevalence of Cutaneous Evaporation in Merriam’S Kangaroo Rat and its Adaptive Variation at the Subspecific Level

Previous estimates suggested that ventilatory evaporation constitutes the major source of water loss in kangaroo rats (Dipodomys spp.). We quantified rates of water loss in Merriam's kangaroo rat (Dipodomys merriami) and demonstrate the degree to which acclimation to a particular thermal and hydric environment plays a role in the intraspecific variation in water loss evident in this species. We draw the following conclusions: (1) that water loss varies intraspecifically in Merriam's kangaroo rat, in association with habitats of contrasting aridity and temperature; (2) that animals from more xeric locations have lower water loss rates than those from more mesic sites; (3) that most water loss is cutaneous, with ventilatory evaporative water loss contributing, at most, only 44% to total evaporative water loss; and (4) that intraspecific differences in rates of water loss are not acclimatory, but fixed. After acclimating under the same conditions, xeric-site animals still show a 33% lower rate of evaporative water loss than mesic-site animals.

Water collection by the body in a viperid snake, Bothrops moojeni

AbstractWe describe a previously unreported behavior for water collection in juveniles of a neotropical viperid snake, Bothrops moojeni. When sprayed over, this snake displays a stereotyped coiling, bringing its body loops in close contact with each other, so that water is retained between the loops and over the body surface. This water is continuously ingested during and after its collection. The functional significance of the water collecting behavior is suggested to be related with the acquisition of water from short rainfalls, and with the special climatic and geologic conditions of B. moojeni habitat. Rates of evaporative water loss did not differ between juvenile and adult snakes, but since juveniles have a greater surface-to-volume ratio, they were significantly more sensitive to desiccation than the adults.

Biodiversity in Southeastern, Seasonally Ponded, Isolated Wetlands: Management and Policy Perspectives for Research and Conservation

BRIDGES is a recurring feature of J-NABS intended to provide a forum for the interchange of ideas and information between basic and applied researchers in benthic science. Articles in this series will focus on topical research areas and linkages between basic and applied aspects of research, monitoring policy, and education. Readers with ideas for topics should contact Associate Editors, Nick Aumen and Marty Gurtz. Isolated wetlands have received little attention as a specific ecosystem type, yet many development and regulatory programs affect them. This lack of recognition may stem from their small size, their variable hydrology, and lack of recognition of their regional significance in the southeast US. In recognition of this problem, and in response to a US National Research Council recommendation for more research in support of wetland protection, a group of individuals convened a workshop to discuss information needs and to develop strategies to protect southeastern isolated wetlands and their biodiversity. Because the organizers perceived a lack of linkage between researchers and managers, workshop participants included scientists, natural resource managers of public and private lands, and conservationists.

Tolerance of forced air emergence by a fish with a broad vertical distribution, the rockpool blenny, Hypsoblennius gilberti (Blenniidae)

Many intertidal fishes, particularly among the Blenniidae and Cottidae, possess amphibious adaptations, including the ability to breathe in air and to avoid desiccation in terrestrial conditions. These traits are absent in subtidal species of blennies and cottids. Hypsoblennius gilberti, the rockpool blenny, is found in shallow rockpools in the mid to high intertidal areas of Southern California, and deeper to 18 m in the subtidal zone. This broad vertical distribution could indicate that this blenny is adapted for tidal air emergence, although H. gilberti has not been observed out of water in its natural habitat. H. gilberti does not emerge voluntarily from hypoxic sea water in the laboratory, but it easily withstands 3 h out of water. The aerial respiratory exchange ratio (CO2 released compared to O2 consumed) is 0.70, similar to that of amphibious intertidal fishes in air, indicating sufficient release of metabolically produced CO2 while emerged. There is no increase in aquatic respiration following emergence. However, unlike other amphibious fishes that maintain aerial oxygen consumption at a level similar to aquatic oxygen consumption, H. gilberti has an aerial oxygen consumption rate one-third that in water. H. gilberti can recover rapidly from terrestrial water loss, and shows no change in evaporative water loss rates at 93% and 77% relative humidities. The amphibious capabilities in H. gilberti, even if rarely used, permit survival in air during tidal emergence. These findings suggest that H. gilberti may demonstrate an intermediate condition between the amphibious species of intertidal fishes that regularly emerge from water, and the subtidal fishes that do not survive air emergence and are completely restricted to an aquatic habitat.

Metabolic Physiology of Euthermic and Torpid Lesser Long-Eared Bats, Nyctophilus geoffroyi (Chiroptera: Vespertilionidae)

Thermal and metabolic physiology of the Australian lesser long-eared bat, Nyctophilias geojfroyi , a small (ca. 8 g) gleaning insectivore, was studied using flow-through respirometry. Basal metabolic rate of N. geojfroyi (1.42 ml O2 g−1 h−1) was 70% of that predicted for an 8-g mammal but fell within the range for vespertilionid bats. N. geoffroyi was thermally labile, like other vespertilionid bats from the temperate zone, with clear patterns of euthermy (body temperature >32°C) and torpor. It was torpid at temperatures ≤25°C, and spontaneously aroused from torpor at ambient temperatures ≥5°C. Torpor provided significant savings of energy and water, with substantially reduced rates of oxygen consumption and evaporative water loss. Minimum wet conductance (0.39 ml O2 g−1 h−1 °C−1) of euthermic bats was 108% of predicted, and euthermic dry conductance was 7.2 J g−1 h−1 °C−1 from 5–25°C. Minimum wet and dry conductances of bats that were torpid at an ambient temperature of 15–20°C (0.06 ml O2 g−1 h−1 °C−1 and 0.60 J g−1 h−1 °C−1) were substantially less than euthermic values, but conductance of some torpid bats increased at lower ambient temperatures and approached values for euthermic bats. Metabolic rates of bats torpid at ambient temperatures >10°C and bats euthermic in the thermoneutral zone indicated a metabolic Q10 of 3.9. That high Q10 suggested that there may have been an intrinsic reduction in metabolic rate during torpor, in addition to down-regulation of thermoregulation (which accounted for most of the reduction in metabolic rate) and the normal Q10 effect.

Computerized evaporimetry using the DermaLab® TEWL probe

Background/aims:TEWL measurements are one of the most frequently utilized of the non‐invasive bioengineering techniques. We wanted to enhance the reproducibility and sensitivity of this method by employing computerized evaporimetry.Methods:A DermaLab® system equipped with one or two TEWL probes was interfaced to a personal computer (PC) via the RS‐232c port and special data acquisition software written so that changes in water loss rates could be monitored in real time. Application programs included TEWL measurements under steadystate or dynamic conditions using single or dual probe instruments as well as diagnostics to determine probe condition. Retrospective analysis could be performed by exporting the captured data to an ExcelTM spread sheet.Conclusions:Computerized evaporimetry, which allows the operator to conveniently monitor evaporative water loss rates in real time, should be the preferred way of making these types of measurements.

Standard Evaporative Water Loss and Metabolism of Juvenile Varanus mertensi (Squamata: Varanidae)

Evaporative water loss (EWL) varies considerably both within and between reptile species (Dmi'el, 1985; Eynan and Dmi'el, 1993; Lahav and Dmi'el, 1996) and can also be affected by acclimation (Hillman et al., 1979; Kobayashi et al., 1983). EWL data are available for a wide variety of reptiles from various habitats (see review by Mautz, 1982) but are limited for goannas under controlled conditions (Warburg, 1965; Green, 1969; Thompson and Withers, 1997a). For lizards, such as goannas, body water is lost by evaporation from the skin (including the eyes) and the respiratory passages and as a mixture of urine and feces (and in some species from nasal salt glands; Green, 1969; Saint Girons et al., 1981). The rate of cutaneous evaporative water loss (CEWL) is largely determined by the exposed surface area of the skin and eyes, the resistance of these surfaces to evaporation, and the difference in water vapor concentrations across the surfaces. The respiratory evaporative water loss (REWL) is determined mainly by the lung ventilation rate and body temperature but may be reduced by nasal countercurrent heat and water exchange (Mautz, 1980). Environmental conditions such as ambient temperature, relative humidity, and wind velocity also affect EWL (Thorpe and Kontogiannis, 1977; Mautz, 1980, 1982). EWL is generally higher for mesic reptiles than arid species (Snyder, 1971; Dmi'el, 1972; Shoemaker and Nagy, 1977), and we would expect the EWL of a semiaquatic goanna to be higher than for comparable terrestrial species. However, there are no data for EWL of semiaquatic goannas under controlled conditions. The semiaquatic goanna Varanus mertensi has a much higher field water turnover (WTR) than predicted for lizards from arid and tropical zones (Christian et al., 1996), but it is not clear whether their high WTR is associated with a high cutaneous EWL, respiratory EWL, water excretion, or a combination thereof. This study examines the standard EWL (EWL,td) and standard metabolic rate (VO2std) for juvenile V mertensi. The primary objectives were to measure total evaporative water loss and calculate resistance to water evaporation under standardized laboratory conditions (TEWLtd, rstd), and to partition TEWLStd and rstd into its respiratory and cutaneous components. Thompson and Withers (1997a) report TEWL,td and resistance to total water loss (rtota) for a number of terrestrial and arboreal Western Australian

Sexual dimorphism in physiological performance of whiptail lizards (genus Cnemidophorus).

Numerous studies have examined sexual dimorphism in the morphology and behavior of vertebrates; very few, however, have explicitly investigated the possibility of gender differences in physiological performance, despite the observations of such differences in humans. In this study, I investigated physiological sexual dimorphism in the lizard genus Cnemidophorus by measuring five whole-animal traits, all of which are likely to influence fitness in these species: burst speed, endurance, maximal exertion capacity, standard metabolic rate, and evaporative water loss rate. Because at least some of these traits are known to be strongly influenced by body size, I tested for dimorphism using both absolute and size-corrected trait values. An examination of six Cnemidophorus species and subspecies revealed a strong trend toward higher absolute trait values in males for all variables except endurance. Most of the dimorphism in standard metabolic rate and evaporative water loss rate could be explained by differences in body mass between males and females; for the locomotor traits, however, body size explained only a small fraction of the overall sexual dimorphism. The portion of trait differences not explained by body size was likely due to gender differences in physiology, such as differences in relative muscularity and fat content.

Thermoregulatory Responses of Bridled and Juniper Titmice to High Temperature

Bridled Titmice (Baeolophus wollweberi) and Juniper Titmice (B. ridgwayi) occur sympatrically in southeastern Arizona, with Bridled Titmice preferring habitats that are more heavily vegetated, moister, and cooler than those occupied by Juniper Titmice. To assess whether these differences in habitat preference have physiological correlates, we measured the oxygen consumption, evaporative water loss, and body temperature of post-breeding titmice at ambient temperatures between 24-44°C. Bridled Titmice were less tolerant of heat than Juniper Titmice and had significantly higher rates of metabolic heat production and evaporative water loss, but not body temperature, at ambient temperatures above 40°C. These differences were entirely attributable to the Bridled Titmouse's smaller body size (10 versus 15 g), and the differences vanished when rates were expressed per unit metabolic mass (mass raised to either the 2/3 or 3/4 power). Within the thermoneutral zone, the rate of evaporative water loss (EWL) was significantly lower in Juniper Titmice than Bridled Titmice, even after accounting for the difference in body size. Reduced EWL is characteristic of species from hotter, drier habitats and suggests that physiology plays a role in these species' habitat preferences.

Periodic arousals in hibernating mammals: is evaporative water loss involved?

1. Using existing data on the rate of cutaneous and pulmonary evaporative water loss (EWL) for hibernating Little Brown Bats (Myotis lucifugus) and on the duration of torpor bouts, body temperature (Tb) and oxygen uptake (VO2) of Golden‐mantled Ground Squirrels (Spermophilus saturatus), the rate of EWL was modelled for ground squirrels hibernating at ambient temperatures (Ta) of –2, 2, 4 and 8 °C. 2. Total EWL showed a curvilinear response to Ta, being lowest at 2 °C and increasing with both increasing and decreasing Ta. EWL at –2 °C was about equal to that at 4 °C. The duration of torpor bouts showed the same curvilinear response to Ta and torpor bout duration at –2 °C was similar to that at 4 °C (8·5 vs 8·3 days, respectively). 3. At Ta≥ 2 °C, where Tb of torpid S. saturatus is not metabolically defended, torpor bout duration is significantly related to Tb, VO2 and EWL, with the three variables having similar r2 values. 4. Using the regression equations generated at Ta≥ 2 °C to predict torpor bout durations at –2 °C, where Tb is metabolically defended, shows that the three variables do not have equivalent predictive abilities. Tb and VO2 predicted torpor bout durations of 15·2 and –40·4 days, respectively, compared with observed durations of 8·5 days at –2 °C. EWL predicted torpor bout durations of 8·4 days or only 0·1 days less than that observed at –2 °C. 5. The relation between torpor bout duration and total EWL was insensitive to major variations in cutaneous EWL. Over Ta ranging from –2 °C to 8 °C, a stepwise multiple regression including Tb, VO2 and EWL as independent variables identified EWL as the only variable significantly correlated with torpor bout duration. 6. Our analyses suggest that torpor bout duration may be influenced by EWL, indicating that animals may need to obtain free water when they arouse. An analysis of the structural and temperature characteristics of ground squirrel hibernacula suggests that they may function as a biological condensing tower. Throughout winter, water should evaporate from the warm lower levels and condense in the colder upper regions and so free water may be available to animals when they arouse.