Energetics of nestling growth and parental effort in Antarctic fulmarine petrels.

Antarctic fulmarine petrels breed in some of the coldest conditions encountered by any bird and their young grow twice as fast as predicted allometrically. To examine the energetic consequences of fast growth in a cold environment, we used the doubly labeled water technique to measure field metabolic rates of adults (three species) and different-aged nestlings (four species) of Antarctic fulmarine petrels in the Rauer Islands, East Antarctica: Antarctic fulmar Fulmarus glacialoides, Antarctic petrel Thalassoica antarctica, Cape petrel Daption capense and snow petrel Pagodroma nivea. We used our data to assess parental effort and, together with literature values on nestling growth and resting metabolic rate, to construct and partition nestling energy budgets. Nestling total energy expenditure and peak daily metabolic rate were significantly higher than predicted allometrically (33-73% and 17-66% higher, respectively), and the relative cost of growth in nestling petrels was among the highest reported for birds (54-72 kJ g(-1)). Parental effort during the nestling-feeding period was identical in adult Cape and Antarctic petrels (3.5 times basal metabolic rate, BMR), and was somewhat (but not significantly) higher in snow petrels (4.6 times BMR). These values are comparable to those of other high-latitude procellariiform birds. Thus, despite the constraints of a compressed breeding season, cold temperatures and fast-growing nestlings, adult Antarctic fulmarine petrels do not work harder than procellariid adults whose chicks grow much more slowly. Our findings suggest that obtaining sufficient food is generally not a constraint for adult fulmarine petrels and that factors operating at the tissue level limit nestling growth rate.

Altitudinal variation in parental energy expenditure by white-crowned sparrows.

We used the doubly labeled water technique to measure daily energy expenditure (DEE) during the incubation and feeding nestling stages in two populations of white-crowned sparrows (Zonotrichia leucophrys) - one montane and migratory, the other coastal and sedentary - that differ in thermal environment and clutch size. We assessed the birds' thermal environment by continuously monitoring (among other variables) operative temperature and wind speed both in the open and within bushes and willow thickets occupied by sparrows. From these measurements, we derived several estimates of the birds' thermal environment, including standard operative temperature (T(es)). Shade air temperature and T(es) averaged 6.6 and 10.3 degrees C lower, respectively, at the montane study site during DEE measurements. The montane population's DEE averaged 24% higher than that of the sea-level population (103.6+/-12.2 versus 83.7+/-9.6 kJ day(-1); means +/- S.D., N=31 and 22, respectively), reflecting both its larger brood size (3.7 versus 2.9) and the colder environment. The DEE:BMR ratio was lowest in the sea-level population (2.1 versus 2.6), but neither population worked to their physiological capacity to produce young. DEE was significantly correlated with temperature across populations, with T(es) explaining 42% of the variation in DEE. Statistically removing the effect of temperature by adjusting DEE to a common temperature reduced the difference in DEE between populations by 34% to 87.7 and 100.8 kJ day(-1), respectively, for sea-level and montane populations. Basal and resting metabolic rates were similar in both populations, implying that greater activity in the montane population accounted for its higher temperature-adjusted DEE. Our results indicate that the thermal context within which behavior occurs can significantly affect interindividual variation in DEE. Attempts to assess reproductive effort by measuring DEE should therefore account explicitly for the effect of temperature.

Effects of weather on daily body mass regulation in wintering dunlin.

We investigated the influence of changes in weather associated with winter storms on mass balance, activity and food consumption in captive dunlin (Calidris alpina) held in outdoor aviaries, and compared the aviary results with weather-related body mass differences in free-living dunlin collected at Bolinas Lagoon, California. Captive birds fed ad libitum increased their body mass at higher wind speeds and lower temperatures, suggesting regulation of energy stores, whereas free-living birds exhibited patterns suggesting thermoregulatory limits on body mass regulation. Daily energy expenditure in aviary dunlin was 2.85 kJ g d(-1), or 2.8x basal metabolic rate (BMR), with thermostatic costs averaging 59 % of daily expenditure. Slight but significant increases in body mass and energy expenditure in captive birds on rainy days, adjusted for possible external water mass, suggested rainfall as a proximate cue in regulating daily body mass. Body mass changes under artificial rainfall indicated similar results, and field masses suggested that free-living birds have greater body mass on days with measurable rainfall. Increased activity costs under artificial rainfall were associated with an increase in maintenance activities, relative to controls. Whether activity costs increased on days with natural rates of rainfall was unclear. Our results are consistent with current hypotheses regarding the role of body mass regulation in providing insurance against increased starvation risk during deteriorating thermal or foraging conditions, or in reducing the costs of extra mass as conditions improve.

Climatic adaptation in Svian standard metabolic rate.

The 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 bird's 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 bird's life history. For example, in tropical species adaptive modifications in SMR correlate with thermal microhabitat. Tropical birds which forage in the sun have SMR's 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 SMR's typical of high latitude birds.

Seasonal acclimatization to temperature in monk parakeets.

Metabolism and insulation of monk parakeets were determined in summer and compared with previously reported winter values. Fasting levels of metabolism were the same in winter and summer during the daytime: nighttime values were significantly lower in winter (6.11 versus 8.20 Wkg-1). Evaporative water loss at 20-30° C was significantly lower in winter (2.24 versus 3.05 mg H2O g-1 h-1). Winter birds were better able to maintain body temperature (Tb) independent of ambient temperature (Ta) below 20° C than were summer birds. Coefficients of dry heat transfer determined for Tb-Ta gradients greater than 10° C were not significantly different for the two seasons. Similarly, the slope of the line relating oxygen consumption to Ta below thermal neutrality (i.e. thermal conductance) was the same in winter and summer birds, indicating no seasonal change in overall body insulation. Literature review revealed a relation between seasonal change in fasting metabolic rate (FMR) and body size in birds. Winter FMR as a fraction of summer FMR is inversely, related to body mass (Mb) by the equation; winter FMR/summer FMR=1.49 Mb -0.077 where Mb is in grams. Thus, in small birds FMR is higher in winter than summer, while for large birds (>200 g) the converse is true.

Temperature regulation and water requirements of the monk parakeet, Myiopsitta monachus.

Monk parakeets have been introduced into North America within the past 15 years and are apparently becoming established in several geographical regions. Several physiological responses of monk parakeets related to climatic tolerance were examined, and it is concluded that the species is equipped physiologically to occupy most climatic situations with the exception of arctic and subarctic regions and waterless deserts. The standard metabolic rate, determined during the winter, was 44% lower at night (1.17 ml O2 g-1 hr-1) than during the day (1.68 ml O2 g-1 hr-1). Monk parakeets are relatively tolerant of low air temperature (Ta) and showed no signs of hypothermia at Ta's as low as-8°C. The birds were unable to maintain body weight on a diet of air-dried seeds without supplemental water. Monk parakeets possess excellent capabilities for increasing evaporative water loss at high Ta's, being able to dissipate up to 153% of their metabolic heat production at 44°C. This species responds to high Ta's with open-mouthed panting. During panting the thick, moist tongue is raised and lowered in synchrony with the thorax. Thus, monk parakeets may employ lingual flutter to augment evaporative cooling; a mechanism analogous to the gular flutter of other nonpasserine birds.