BackgroundResearch on variation in bill morphology has focused on the role of diet. Bills have other functions, however, including a role in heat and water balance. The role of the bill in heat loss may be particularly important in birds where water is limiting. Song sparrows localized in coastal dunes and salt marsh edge (Melospiza melodia atlantica) are similar in size to, but have bills with a 17% greater surface area than, those that live in mesic habitats (M. m. melodia), a pattern shared with other coastal sparrows. We tested the hypotheses that sparrows can use their bills to dissipate “dry” heat, and that heat loss from the bill is higher in M. m. atlantica than M. m. melodia, which would indicate a role of heat loss and water conservation in selection for bill size.Methodology/Principal FindingsBill, tarsus, and body surface temperatures were measured using thermal imaging of sparrows exposed to temperatures from 15–37°C and combined with surface area and physical modeling to estimate the contribution of each body part to total heat loss. Song sparrow bills averaged 5–10°C hotter than ambient. The bill of M. m atlantica dissipated up to 33% more heat and 38% greater proportion of total heat than that of M. m. melodia. This could potentially reduce water loss requirements by approximately 7.7%.Conclusions/SignificanceThis >30% higher heat loss in the bill of M. m. atlantica is independent of evaporative water loss and thus could play an important role in the water balance of sparrows occupying the hot and exposed dune/salt marsh environments during the summer. Heat loss capacity and water conservation could play an important role in the selection for bill size differences between bird populations and should be considered along with trophic adaptations when studying variation in bill size.

Ectothermic lizards become endothermic in the breeding season, supporting a parental care model for the origins of endothermy.

Metabolic functions are generally optimized within a narrow range of body temperatures (T(b)'s), conferring thermoregulation great importance to the survival and fitness of an animal. In lizards, T(b) regulation is mainly behavioral, and the metabolic costs associated with behavioral thermoregulation are primarily locomotory. In reptiles, however, it has been proposed that they thermoregulate less precisely when the associated costs, metabolic or otherwise, are high. Such a strategy enhances fitness by allowing lizards to be more flexible to changing environmental conditions while maximizing the benefits of maintaining a high T(b) and minimizing energy expenditure. We evaluated the behavioral thermoregulation of inland bearded dragons Pogona vitticeps under various thermal quality conditions requiring different locomotory investment for thermoregulation. The selected ambient temperature and preferred T(b) ranges increased at lower environmental thermal qualities, indicating a decrease in thermoregulatory precision in environments where the costs associated with thermoregulation were high. The level of thermoregulation was also affected, exhibiting a decrease in preferred T(b) of approximately 2 degrees C at the lowest-thermal-quality treatment. These data provide important implications for the procedural assessment of preferred T(b) and a better understanding of thermal set points in reptiles in general. Our results emphasize that the precise maintenance and assessment of preferred T(b) is contingent on the quality of the environment, laboratory or natural, that the animal inhabits.

Infrared thermal technology allows for the real-time visualisation of fixed or transient changes in the long-wave radiative energy emanating from an object, in essence, allowing for the estimation of surface temperature. Animal surface temperatures are, therefore, readily detected using this technology, allowing for the assessment of physiological responses associated with the regulation of body temperature. In this paper, we will introduce some recent advances made possible or enhanced through the use of thermal imaging. In particular, this imaging technology has shed light on the regulation of peripheral blood flow in endothermic animals, on the dynamics of animal heat transfer in complex thermal environments, on the production of heat associated with metabolism and on the importance of evaporative heat loss to respiratory function and its potential contribution to preventing overheating of the brain. More than a simple imager for temperature, this technology has the potential to contribute a greater understanding of animal thermal adaptations, not only since it provides live information on surface temperatures, but more importantly because its non-invasive nature which allows measurements to be obtained with minimal disturbance.

Animal coloration has multiple functions including thermoregulation, camouflage, and social signaling, and the requirements of each function may sometimes conflict. Many terrestrial ectotherms accommodate the multiple functions of color through color change. However, the relative importance of these functions and how colorchanging species accommodate them when they do conflict are poorly understood because we lack data on color change in the wild. Here, we show that the color of individual radio-tracked bearded dragon lizards, Pogona vitticeps, correlates strongly with background color and less strongly, but significantly, with temperature. We found no evidence that individuals simultaneously optimize camouflage and thermoregulation by choosing light backgrounds when hot or dark backgrounds when cold. In laboratory experiments, lizards showed both UV-visible (300-700 nm) and near-infrared (700-2,100 nm) reflectance changes in response to different background and temperature treatments, consistent with camouflage and thermoregulatory functions, respectively, but with no interaction between the two. Overall, our results suggest that wild bearded dragons change color to improve both thermoregulation and camouflage but predominantly adjust for camouflage, suggesting that compromising camouflage may entail a greater potential immediate survival cost.

Many terrestrial ectotherms are capable of rapid colour change, yet it is unclear how these animals accommodate the multiple functions of colour, particularly camouflage, communication and thermoregulation, especially when functions require very different colours. Thermal benefits of colour change depend on an animal's absorptance of solar energy in both UV-visible (300-700 nm) and near-infrared (NIR; 700-2600 nm) wavelengths, yet colour research has focused almost exclusively on the former. Here, we show that wild-caught bearded dragon lizards (Pogona vitticeps) exhibit substantial UV-visible and NIR skin reflectance change in response to temperature for dorsal but not ventral (throat and upper chest) body regions. By contrast, lizards showed the greatest temperature-independent colour change on the beard and upper chest during social interactions and as a result of circadian colour change. Biophysical simulations of heat transfer predicted that the maximum temperature-dependent change in dorsal reflectivity could reduce the time taken to reach active body temperature by an average of 22 min per active day, saving 85 h of basking time throughout the activity season. Our results confirm that colour change may serve a thermoregulatory function, and competing thermoregulation and signalling requirements may be met by partitioning colour change to different body regions in different circumstances.

SUMMARYThe objectives of this study were to compare the thermoregulatory, metabolic and ventilatory responses to hypoxia of the high altitude bar-headed goose with low altitude waterfowl. All birds were found to reduce body temperature (T b ) during hypoxia, by up to 1-1.5°C in severe hypoxia. During prolonged hypoxia, T b stabilized at a new lower temperature. A regulated increase in heat loss contributed to T b depression as reflected by increases in bill surface temperatures (up to 5°C) during hypoxia. Bill warming required peripheral chemoreceptor inputs, since vagotomy abolished this response to hypoxia. T b depression could still occur without bill warming, however, because vagotomized birds reduced T b as much as intact birds. Compared to both greylag geese and pekin ducks, bar-headed geese required more severe hypoxia to initiate T b depression and heat loss from the bill. However, when T b depression or bill warming were expressed relative to arterial O 2 concentration (rather than inspired O 2 ) all species were similar; this suggests that enhanced O 2 loading, rather than differences in thermoregulatory control centres, reduces T b depression during hypoxia in bar-headed geese. Correspondingly, bar-headed geese maintained higher rates of metabolism during severe hypoxia (7% inspired O 2 ), but this was only partly due to differences in T b . Time domains of the hypoxic ventilatory response also appeared to differ between bar-headed geese and low altitude species. Overall, our results suggest that birds can adjust peripheral heat dissipation to facilitate T b depression during hypoxia, and that bar-headed geese minimize T b and metabolic depression as a result of evolutionary adaptations that enhance O 2 transport.

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