Energy Costs Of Thermoregulation Research Articles

Physical constraints on thermoregulation and flight drive morphological evolution in bats

Body size and shape fundamentally determine organismal energy requirements by modulating heat and mass exchange with the environment and the costs of locomotion, thermoregulation, and maintenance. Ecologists have long used the physical linkage between morphology and energy balance to explain why the body size and shape of many organisms vary across climatic gradients, e.g., why larger endotherms are more common in colder regions. However, few modeling exercises have aimed at investigating this link from first principles. Body size evolution in bats contrasts with the patterns observed in other endotherms, probably because physical constraints on flight limit morphological adaptations. Here, we develop a biophysical model based on heat transfer and aerodynamic principles to investigate energy constraints on morphological evolution in bats. Our biophysical model predicts that the energy costs of thermoregulation and flight, respectively, impose upper and lower limits on the relationship of wing surface area to body mass (S-MR), giving rise to an optimal S-MR at which both energy costs are minimized. A comparative analysis of 278 species of bats supports the model’s prediction that S-MR evolves toward an optimal shape and that the strength of selection is higher among species experiencing greater energy demands for thermoregulation in cold climates. Our study suggests that energy costs modulate the mode of morphological evolution in bats—hence shedding light on a long-standing debate over bats’ conformity to ecogeographical patterns observed in other mammals—and offers a procedure for investigating complex macroecological patterns from first principles.

The use of the nest for parental roosting and thermal consequences of the nest for nestlings and parents

At temperate latitudes, altricial birds and their nestlings need to handle night temperatures well below thermoneutrality during the breeding season. Thus, energy costs of thermoregulation might constrain nestling growth, and low nocturnal temperatures might require resources that parents could otherwise have invested into nestlings during the day. To manipulate parental work rate, we performed brood size manipulations in breeding marsh tits (Poecile palustris). Nest box temperatures were always well above ambient temperature and increased with increasing brood size. In line with predictions, a large majority of females (but no males) made use of this benign environment for roosting. Furthermore, females tending enlarged broods, thereby having to work harder during the day, reduced their body temperature at night. This might have reduced nocturnal energy expenditure. Our finding that a higher proportion of enlarged, as compared to control, females continued to use the nest box as roosting sites even after a simulated predation event despite increased vulnerability to predation, further highlighting the need for energy conservation in this group. High nest box attendance and reduced body temperature in brood-reduced females may indicate that these females prioritised self-maintenance by initiating other costly physiological adjustments, e.g. moult, when relieved from parental work. We suggest that the energy demand for defending homeothermy is an element of the general trade-off between current and future reproduction, i.e. between daytime investment in food provisioning and the potential short- and long-term costs of a reduction in body temperature and increased predation risk.Significance statementEven during summer at temperate latitudes, breeding birds need to use energy to maintain stable body temperature. Parents, thus, need to enter the night with sufficient body reserves to cover energy requirements for thermoregulation. As these resources could be used for feeding nestling during the day, adaptations to reduce the cost of thermoregulation would be selected for. We performed brood size manipulations, thereby increasing the need for nestling provisioning in marsh tits (Parus palustris). We found that females typically spent the night in the thermally benign environment of the nest box together with their brood. Females working hard during the day continued to roost in the nest box during the night despite an increase in the perceived risk of nest predation. Furthermore, these females reduced their body temperature at night, thereby reducing the gradient between ambient and body temperature, further reducing the cost of thermoregulation.

Thermal and energetic consequences of nest location and breeding times in Water Pipits (Anthus spinoletta)

The thermal environment has pronounced effects on the energy costs of thermoregulation and affects an animal's allocation of energy to self-maintenance and parental care. Consequently, the selection of reproductive periods, breeding habitats and nest-sites with a favourable microclimate can be advantageous, especially for birds breeding in harsh environments. In this study on Alpine Water Pipits (Anthus spinoletta), we evaluate the importance of spatial and temporal factors on thermoregulatory costs by combining laboratory measurements of metabolic rates under various temperatures with standard operative temperatures (Tes) recorded in the field in different microhabitats. Using these measurements we estimate the thermal and energetic consequences of nest locality and timing of reproduction. Our results show: (1) In the morning, Tes values were much higher on the east-north-east (ENE) slope of a valley than on the west-south-west (WSW) slope; in the afternoon this pattern was reversed. As a consequence, energy costs (Ehour) for thermoregulation on the ENE slope were up to 0.6 RMR (resting metabolic rate at night) lower than on the WSW slope during morning hours and about 0.8 RMR higher during afternoon hours. (2) During the incubation and nestling phases of first and second broods, total energy expenditure for thermoregulation in the daytime (Edaytime) was 0.2–0.3 RMR higher on the ENE slope than on the WSW slope. (3) Within slopes, Edaytime was lower during second broods than during first broods, with differences of 0.06–0.07 RMR during incubation and of 0.32 RMR during nestling care. These differences correspond to the flying costs of females incubating eggs (0.09 RMR) and rearing nestlings (0.25 RMR). We conclude that nest placement in relation to microclimate can improve the female's energy budget, both in terms of the total daily expenditure and its diurnal pattern. From thermal considerations alone, delaying breeding into mid-summer would be advantageous, but this advantage is probably outweighed by the reduced chances for second and replacement clutches and by the necessity to complete moult before migration.

A spatial energetics model of cadmium accumulation by diving ducks

Food-chain transfer of contaminants is often predictable below the level of birds, but relations between contaminant concentrations in birds and their foods are often weak and variable. Much of this variation probably results from the energetics of foraging in fluctuating, heterogeneous environments, which has not been accounted for in past models of contaminant uptake by birds. Because birds are highly mobile with varying lengths of stay in different areas, collecting birds and analyzing their tissues yields unclear information on the importance of local contaminants. Likewise, toxicity assays with captive birds ignore changes in food intake with varying activity and weather experienced by wild birds. Neither of these approaches alone can predict maximum allowable contaminant levels in foods that avoid toxic effects under different field conditions, or what body burdens accumulate during varying lengths of stay that might affect the birds' biology at other places and times. To allow such predictions, an individual-based computer model was developed to simulate the intake of contaminated foods by diving ducks for varying conditions such as weather, water depth, food dispersion, and the size and digestibility of food. Food-intake estimates are combined with laboratory data on contaminant uptake as a function of food consumption and contaminant content. As an example, cadmium uptake is estimated for Canvasback ducks (Aythya valisineria) foraging on belowground winter buds of the submerged plant Vallisneria americana. Results indicate that relations between cadmium content of food and cadmium uptake by kidneys can be quite different depending on field conditions, and that cadmium content of food can be less important than food dispersion and resulting search costs in determining cadmium uptake. Models that estimate food intake based on energetic profitability can yield very different predictions than models that assume constant daily intake, or assume that food intake simply increases as energy costs of thermoregulation or other factors go up. Such profitability effects might explain much of the confounding variation in deriving bioaccumulation factors for birds.

Winter ecology of nonmigratory Alpine red deer.

In winter, red deer (Cervus elaphus hippelaphus) that are not receiving supplementary feeding emphasize and rely on energy-saving strategies. In severe winters with deep snow, they select a home-range habitat-windblown alpine pastures above the timberline-that meets the requirements of this strategy: a much lower sinking depth and good forage availability are due to patchy snow distribution, while the open area provides higher radiation, permits group formation and thus sociobiological wellbeing. The energy costs of thermoregulation are minimized by selecting slopes with south to south-west exposures, seeking thermal shelter from strong winds, while high flight distances and horizontal flight routes reduce the energy costs of fleeing. In years with little winter snowfall non-supplemented red deer prefer the greater security of forested habitats in lower areas and obtain higher food intake from slightly more nutritious meadows in the valley bottom. The food-supplemented herd has much more constant and predictable habitat use, combining an energy-saving strategy-choosing alpine pastures as low-cost winter home range-with high energy income at the feeding station.

Standard Operative Temperatures and Thermal Energetics of the Antelope Ground Squirrel Ammospermophilus leucurus

We measured standard operative temperatures ($T_{es}$) for the diurnal ground squirrel Ammospermophilus leucurus in its Southern California desert habitat by using pelt-covered metal models of the animals. Values of $T_{es}$ were used to predict duration of periods of activity, microhabitat use, and energy costs of thermoregulation at various times of the year. For A. leucurus, $T_{es}$ (a direct measure of heat flow) specifies the thermal environment more realistically than any of the standard micrometeorological indices. In the hot season, $T_{es}$ in unshaded areas can be 30 C above the upper critical temperature ($T_{uc}$) of A. leucurus and 20 C above air temperature for much of the day. Under such conditions maximum tolerable periods of surface activity for A. leucurus are 7-9 min. Even in the shade, $T_{es}$ often exceeds $T_{uc}$, and the only available thermal refugia on hot days are in underground burrows. These findings strongly support the interpretation that the thermoregulatory strategy of A...

The Influence of Simulated Solar Radiation on the Metabolic Rate of White-Crowned Sparrows

energy costs of thermoregulation by behaviorally exploiting sources and sinks of radiation of various wavelengths. For example, sunbathing while in cool surroundings is interpreted as an important mode of behavioral thermoregulation (Hamilton and Heppner 1967, Morton 1967, Ohmart and Lasiewski 1971) although additional functions for sunbathing are also plausible (Simmons 1964, Cowles et al. 1967, Goodwin 1967, Teager 1967, Kennedy 1968, Mueller 1972, Cade 1973). In spite of increasing attention to the role of insolation in the energy economy of homeotherms (Bakken 1959, Whittow 1970, Marder 1973), there have been no systematic empirical investigations of the interacting effects of air temperature and solar radiation in the energetics of thermoregulation in wild species of animals. Our quantitative appreciation of the ecological significance of such interactions depends at present on rather large-scale theoretical models of climate space (Porter and Gates 1989, Gates and Porter 1970) that serve only to delimit the temperature-radiation boundaries within which an animal can function in a