Viviana Cadena

Heat Loss May Explain Bill Size Differences between Birds Occupying Different Habitats

Background Research 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 Findings Bill, 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/Significance This >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.

Body temperature depression and peripheral heat loss accompany the metabolic and ventilatory responses to hypoxia in low and high altitude birds

SUMMARY The 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 (Tb) during hypoxia, by up to 1–1.5°C in severe hypoxia. During prolonged hypoxia, Tb stabilized at a new lower temperature. A regulated increase in heat loss contributed to Tb 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. Tb depression could still occur without bill warming, however, because vagotomized birds reduced Tb as much as intact birds. Compared to both greylag geese and pekin ducks, bar-headed geese required more severe hypoxia to initiate Tb depression and heat loss from the bill. However, when Tb depression or bill warming were expressed relative to arterial O2 concentration (rather than inspired O2) all species were similar; this suggests that enhanced O2 loading, rather than differences in thermoregulatory control centres, reduces Tb depression during hypoxia in bar-headed geese. Correspondingly, bar-headed geese maintained higher rates of metabolism during severe hypoxia (7% inspired O2), but this was only partly due to differences in Tb. 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 Tb depression during hypoxia, and that bar-headed geese minimize Tb and metabolic depression as a result of evolutionary adaptations that enhance O2 transport.

Respiratory cooling and thermoregulatory coupling in reptiles

Comparative physiological research on reptiles has focused primarily on the understanding of mechanisms of the control of breathing as they relate to respiratory gases or temperature itself. Comparatively less research has been done on the possible link between breathing and thermoregulation. Reptiles possess remarkable thermoregulatory capabilities, making use of behavioural and physiological mechanisms to regulate body temperature. The presence of thermal panting and gaping in numerous reptiles, coupled with the existence of head-body temperature differences, suggests that head temperature may be the primary regulated variable rather than body temperature. This review examines the preponderance of head and body temperature differences in reptiles, the occurrence of breathing patterns that possess putative thermoregulatory roles, and the propensity for head and brain temperature to be controlled by reptiles, particularly at higher temperatures. The available evidence suggests that these thermoregulatory breathing patterns are indeed present, though primarily in arid-dwelling reptiles. More importantly, however, it appears that the respiratory mechanisms that have the capacity to cool evolved initially in reptiles, perhaps as regulatory mechanisms for preventing overheating of the brain. Examining the control of these breathing patterns and their efficacy at regulating head or brain temperature may shed light on the evolution of thermoregulatory mechanisms in other vertebrates, namely the endothermic mammals and birds.

The Effect of Thermal Quality on the Thermoregulatory Behavior of the Bearded Dragon Pogona vitticeps: Influences of Methodological Assessment

Metabolic functions are generally optimized within a narrow range of body temperatures (Tbs), conferring thermoregulation great importance to the survival and fitness of an animal. In lizards, Tb 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 Tb 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 Tb 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 Tb of ∼2°C at the lowest‐thermal‐quality treatment. These data provide important implications for the procedural assessment of preferred Tb and a better understanding of thermal set points in reptiles in general. Our results emphasize that the precise maintenance and assessment of preferred Tb is contingent on the quality of the environment, laboratory or natural, that the animal inhabits.

Seasonal reproductive endothermy in tegu lizards.

Ectothermic lizards become endothermic in the breeding season, supporting a parental care model for the origins of endothermy. With some notable exceptions, small ectothermic vertebrates are incapable of endogenously sustaining a body temperature substantially above ambient temperature. This view was challenged by our observations of nighttime body temperatures sustained well above ambient (up to 10°C) during the reproductive season in tegu lizards (~2 kg). This led us to hypothesize that tegus have an enhanced capacity to augment heat production and heat conservation. Increased metabolic rates and decreased thermal conductance are the same mechanisms involved in body temperature regulation in those vertebrates traditionally acknowledged as “true endotherms”: the birds and mammals. The appreciation that a modern ectotherm the size of the earliest mammals can sustain an elevated body temperature through metabolic rates approaching that of endotherms enlightens the debate over endothermy origins, providing support for the parental care model of endothermy, but not for the assimilation capacity model of endothermy. It also indicates that, contrary to prevailing notions, ectotherms can engage in facultative endothermy, providing a physiological analog in the evolutionary transition to true endothermy.

Decreased precision contributes to the hypoxic thermoregulatory response in lizards.

SUMMARY The decrease in body temperature (Tb) observed in most vertebrate classes in response to hypoxia has been attributed to a regulated decrease in set-point, protecting organs against tissue death due to oxygen depletion. Hypoxia, however, imparts particular challenges to metabolic function which may, in turn, affect thermoregulation. In ectotherms, where thermoregulation is mainly behavioural, stressors that influence the propensity to move and respond to temperature gradients are expected to have an impact on thermoregulatory control. Using low oxygen as a potent stressor, we evaluated the variability and level of thermoregulation of inland bearded dragons. To examine the source of thermoregulatory variability, we studied their behaviour in an electronically controlled temperature-choice shuttle box, a constant temperature dual-choice shuttle box, and a linear thermal gradient. A significant increase in the size of the Tb range was observed at the lowest oxygen concentration (4% O2), reflecting a decrease in thermoregulatory precision in the temperature-choice shuttle box. This was also accompanied by a drop of ∼2–4°C in Tb, the drop being greatest in situations where Tb must be actively defended. Situations that force the lizards to continually choose temperatures, rather than passively remain at a given temperature, lead to an increase in the variability in the manifested Tb, which is further exaggerated in hypoxia. This study reveals that a decrease in thermoregulatory precision caused by a diminished propensity to move or effect appropriate thermoregulatory responses may be a contributing component in the lowering of selected body temperatures observed in many hypoxic ectotherms.

LIZARD WITS INCREASE AS PLANET HEATS

![][1] We all know an animal is the product of its genes and the influence of the environment. Humidity, food availability and parental care are just examples of factors that can have a strong impact on an animals characteristics. This is certainly true in the case of reptiles, where

LET US LAUGH TO EASE THE PAIN

![][1] We all have experienced the positive effects of laughter. It induces a deep state of relaxation and a sense of well-being. It is also an important form of non-verbal communication that allows others to know we agree that something is funny. In this way, laughter strengthens

THE NOT-SO-PLAIN DUET OF THE PLAIN-TAILED WREN

![][1] Among the beautiful, colourful birds inhabiting the Andean mountains of Ecuador, plain-tailed wrens seem rather underwhelming; little drab-looking birds hopping around bamboo thickets looking for the insects that will be their next meal. However, despite their dull appearance,

NO MOM, NO PEACE FOR RHESUS MONKEYS

![Figure][1] Stress at an early age can have important consequences on the behaviour and brain development of an animal. For example, in their 2000 publication in Primates , Drago and Thierry found that when baby Tonkean Macaques were separated from their mothers they became aggressive and