Wesley W. Weathers

Climatic adaptation in Svian standard metabolic rate

SummaryThe standard metabolic rate (SMR) of birds correlates broadly with climate of origin. SMR tends to be higher in birds from cold climates and lower in tropical forms than would be expected from the birds mass. SMR changes, on the average, 1% per degree change in latitude. The influence of climate on SMR is, however, subject to modification by other aspects of the birds life history. For example, in tropical species adaptive modifications in SMR correlate with thermal microhabitat. Tropical birds which forage in the sun have SMRs averaging 25% lower than expected, while SMR of species which forage in the shade is normal. Species of penguins which undergo prolonged fasts during the breeding season do not show elevated SMRs typical of high latitude birds.

TEMPERATURE ADAPTATIONS IN AMPHIBIANS

Past studies of ecogeographic character variations have failed to provide a quantitative relationship between the character being measured and the environmental parameter which impinges upon that character. We offer an example in amphibians directly relating a character variation, the range of temperature tolerance, and the critical environmental parameter for that character, the environmental temperature variation. In this example, the range of temperature tolerance is closely related to the environmental temperature variations. Where the environmental temperature variation increases so does the range of temperature tolerance. In addition, where environmental temperatures decrease, the capacity to tolerate such temperatures is lost. These data are consistent with the thesis that congeneric and conspecific populations in different habitats have partially independent evolutionary pathways and that where populations have been displaced from a less to a more uniform environment, characters which are no longer maintained by selection pressure are lost.

Time-Budget Estimates of Avian Energy Expenditure: Physiological and Meteorological Considerations

Daily energy expenditures (Htd) of aviary-housed budgerygahs (Melopsittacus undulatus) were estimated simultaneously using doubly labeled-water (DLW) and timebudget (TB) methods under summer and winter conditions. Laboratory validation of the DLW technique displayed excellent agreement with concomitant gravimetric measures of CO₂ production (algebraic mean difference = -0.04%; range = -5.2%-6.2%). The aviary studies combined continuous 24-h recording of each birds daily activities with quantification of its thermal environment (wind speed and air and operative temperatures). Activity and thermoregulatory costs of birds used for TB studies were measured in the laboratory. Comparison of Htds predicted by DLW to values predicted by the TB method indicate that measurement of activity costs at the time of the study and their subsequent evaluation through existing heat-transfer models are equally important to determining reliable energy budgets. Avian TB studies that fail to address these concerns are prone to systematic biases in their estimates of Htd.

Heat Produced as a By-Product of Foraging Activity Contributes to Thermoregulation by Verdins, Auriparus flaviceps

To test the hypothesis that heat produced as a by-product of physical activity substitutes for avian thermoregulatory requirements, we measured daytime CO₂ production of a very active small passerine, the verdin (Auriparus flaviceps), at various standard operative temperatures (Tes). We used the doubly labeled water method to measure active period field metabolic rates (FMRα) of verdins in their natural habitat, and compared our results to laboratory measurements of daytime resting metabolism (RMRα) and time-budget (TB) estimates of FMRα. Active-period metabolic expenditures decreased with increasing Tes, but the temperature dependence of FMRα difered from that of FMRα such that in the cold the two functions converged. TB estimates of FMRα (computed by a model assuming activity costs were additive) were higher than measured FMRα at low Tes. These results support the hypothesis that proportional substitution of exercise thermogenesis partially accommodates thermoregulatory requirements of small, free-ranging birds.

Testosterone increases activity but not daily energy expenditure in captive male dark-eyed juncos, Junco hyemalis

Plasma testosterone (T) levels in male dark-eyed juncos peak early in the breeding season, then decline. If T enhances opportunities for reproductive success, as suggested by previous experiments, why does elevated T not occur naturally? To address this question, we prolonged the early peak level throughout the breeding season and explored potential energetic costs of maintaining elevated T. We measured daily energy expenditure (DEE) of treated males (T-males) and controls (C-males) using doubly labelled water (DLW). We also conducted behaviour scans of T- and C-males housed in outdoor aviaries. DEE was not higher in T-males than in C-males. However, T-males did increase locomotion and foraging and decrease rest and self-maintenance. These results suggest that elevated T may increase the contribution of some components of DEE and lower the contribution of others. Furthermore, the T-induced decrease in allocation of time to rest and maintenance may represent a long-term cost that has led to selection against the maintenance of elevated T beyond the natural early spring peak. Copyright 2000 The Association for the Study of Animal Behaviour.

A simple technique for estimating operative environmental temperature

Abstract 1. 1.|Operative environmental temperature (Tc) is commonly measured using a taxidermic mount consisting of a hollow copper cast of an animals body covered by the animals integument. We compare estimates of Tc made using such mounts with those derived from use of painted metal sphere thermometers, which are easier to construct and more rugged than taxidermic mounts. 2. 2.|Comparison of data for 4 bird species indicates that metal spheres may be acceptable Tc-thermometers for analyses involving multiple measurements over moderately long time-scales (e.g. several hours). 3. 3.|In this case, positive and negative differences between operative temperature estimated from use of taxidermic mounts and painted spheres tend to compensate and the average difference is usually less than 2°C. This difference is similar to that resulting from postural variation of taxidermic mounts or variation among individual mounts in identical postures. 4. 4.|Sensitivity analysis indicates that use of painted spheres is unlikely to be an important source of error in estimates of total daily energy expenditure. 5. 5.|In contrast, use of painted sphere thermometers in analyses involving fewer measurements over shorter-time scales can produce unacceptable discrepancies from values obtained from taxidermic mounts (i.e. up to 6.3°C).

Metabolic and behavioral responses of American kestrels to food deprivation

1. 1. The effect of short-term (79 hr) food deprivation at 27°C on body mass, locomotor activity, body temperature (Tb), and resting oxygen consumption was determined in eleven American kestrels (Falco sparverius). 2. 2. The change in body mass during resting followed the relation, % mass remaining = 99 e0.07(days fasting). There was no significant difference in the rate of relative mass loss between males and females. 3. 3. Locomotor activity, measured as perch hopping, was highly variable in both control and fasted birds and showed no correlation with stage of the fast, basal metabolic rate (BMR), or rate of mass loss during food deprivation. 4. 4. Body temperatures of fasted birds declined continuously by 0.2–0.4°C per day from 39.3 to 38.3°C. 5. 5. Both males and females responded to food deprivation with a decrease in metabolism. By the third night of fasting, BMR had declined 23.4% from 0.845 W (bird day)−1 to 0.647 W (bird day)−1. The observed reduction in BMR is 2.4 times that expected from a 1°C decline in Tb (assuming Q10 = 2.5) indicating active suppression of metabolism.

Thermal ecology and ecological energetics of California spotted owls

Abstract In this study, we used open-circuit respirometry and the doubly labeled water technique (DLW) to examine the thermal ecology and ecological energetics of California Spotted Owls (Strix occidentalis occidentalis). Our physiological and behavioral observations indicated that Spotted Owls are less heat tolerant than typical birds. At temperatures above the thermoneutral zone (18.2–35.2°C), resting metabolic rate increased 1.48 times faster than predicted allometrically, and behavioral responses to heat stress (increased breathing rate, ptiloerection, gaping, and wing drooping) occurred at relatively modest temperatures, 30–34°C. Our data support the hypothesis that Spotted Owls prefer old-growth and late seral stage forests because they provide favorable microclimates. Our metabolic measurements reveal that Spotted Owls have exceptionally low energy requirements. Their basal metabolic rate, 10.13 ± 0.46 J g−1 hr−1, is only 82% of that predicted allometrically for owls. Field metabolic rate (FMR) of five adults provisioning dependent young averaged 249 ± 60 kJ day−1, only 34% of that predicted for comparably sized non-passerine birds. We calculated Spotted Owl prey requirements from our FMR data, laboratory determinations of assimilation efficiency (77%), and the body composition of representative prey types. On average, Spotted Owls feeding young can meet their own energy needs by consuming one northern flying squirrel (Glaucomys sabrinus) every 1.8 days or one woodrat (Neotoma fuscipes) every 3.7 days. Ecología Térmica y la Energética Ecológica de Strix occidentalis occidentalis Resumen. En este estudio usamos respirometría de circuito abierto y la técnica de agua doble-marcada (DLW) para examinar la ecología térmica y la energética ecológica de la lechuza moteada californiana (Strix occidentalis occidentalis). Nuestras observaciones fisiologicas y comportamentales indican que las lechuzas moteadas son menos tolerantes a temperaturas elevadas que las aves en general. A temperaturas sobre de la zona de neutralidad térmica (18.2–35.2°C), la tasa metabólica basal se incrementó 1.48 veces más rápido que la predicha alométricamente, y la respuesta en el comportamiento a la tensión térmica (incremento en la tasa respiratoria, erección de las plumas, jadeo y el reposo de las alas) ocurrió a temperaturas relativamente bajas (30–34°C). Nuestros datos son consistentes con la hipótesis que las lechuzas moteadas prefieren bosques maduros y en etapas avanzadas de suseción debido a su microclima favorable. Nuestras medidas metabólicas indican que las lechuzas moteadas tienen requerimientos energéticos excepcionalmente bajos. Su tasa metabólica basal, 10.13 ± 0.46 J g−1 hr−1, representa solo el 82% del valor predicho para lechuzas. La tasa metabólica de campo (TMC) de cinco adultos que se encuentraban criando polluelos promedió 249 ± 60 kJ day−1, solamente un 34% del valor predicho para aves no-paserinas de tamaño comparable. Calculamos los requisitos de alimentación para lechuzas moteadas usando nuestros datos de TMC, las determinaciones en el laboratorio de la eficiencia de la asimilación (77%), y la composición corporal de varios tipos de alimentos. En promedio, las lechuzas moteadas criando polluelos pueden mantenerse alimentandose de una ardilla (Glaucomys sabrinus) cada 1.8 días o una rata (Neotoma fuscipes) cada 3.7 días.

Effect of wind and air temperature on metabolic rate in verdins, Auriparus flaviceps

We measured oxygen consumption and cloacal body temperature of verdins (Auriparus flaviceps) in a wind tunnel metabolism chamber at combinations of air temperature and wind speed ranging from 5 to 35 C and 0.05 to 3.0 m/s, respectively. Metabolic rate correlated positively with wind speed at all air temperatures. The wind speed dependence of metabolism was negatively correlated with chamber air temperature such that wind had a greater influence on metabolic rate at low temperatures. Total thermal resistance of verdins decreased with increasing wind at all air temperatures. Body (tissue plus coat) thermal resistance decreased with wind also, indicating that plumage insulation was disrupted by forced convection. We used a convection-adjusted time budget model to estimate the daily energy requirements of wintering verdins and found that moderate increases in mean daily wind speed caused 20%-30% increases in estimated verdin daily energy expenditure. Our results demonstrate the importance of winds effects on the energy budgets of small birds.

Energy cost of incubation in the canary

1. 1. At temperatures below the thermoneutral zone (TNZ) canaries Serinus canaria consumed more oxygen when incubating clutches of either 2 or 4 to 5 eggs, than when perched outside the nest. 2. 2. Within the TNZ, oxygen consumption (.VO2) of incubating and perching birds was not significantly different, and averaged 108% of the value predicted from mass. 3. 3. The lower critical temperature (T1c) was 1.5 to 4.5°C higher in incubating birds. 4. 4. At temperatures below the T1c, .VO2 of incubating birds increased by a constant fraction over that of perching birds, averaging about 6% for 2-egg clutches and 19% for 4- or 5-egg clutches.