Dirkjan Masman

Intraspecific Allometry of Basal Metabolic Rate: Relations with Body Size, Temperature, Composition, and Circadian Phase in the Kestrel, Falco tinnunculus

The relationship between body size and basal metabolic rate (BMR) in homeo therms has been treated in the literature primarily by comparison between species of mammals or birds. This paper focuses on the intraindividual changes in BMR when body mass (W) varies with different maintenance regimens. BMR varied in individual kestrels in proportion to W1.67, which is considerably steeper than the mass exponents for homomorphic change (0.667; Heusner, 1984) for interspecific comparison among all birds (0.677) or raptors (0.678), for interindividual comparison of kestrels on ad libitum maintenance regimens (0.786), and for mass proportionality (1.00). The circadian range of telemetered core temperature also varied more strongly with intraindividual than with interspecific (Aschoff, 1981a) variation in mass. This was due to reduced nocturnal core temperature at low-maintenance regimens, which was, however, insufficient to account for the excessive reduction in BMR. Carcass analysis of eight birds sacrificed revealed a disproportionate reduction in heart and kidney lean mass at low-maintenance regimens. We surmise that variation in BMR primarily reflects variation in these metabolically highly active tissues. This may account for positive correlations found between heart, kidney, and BMR residuals relative to interspecific allometric prediction, and between α and p residuals, as expected on the basis of the constant excess of BMR during α above BMR during p (Aschoff & Pohl, 1970a).

Energetic limitation of avian parental effort : Field experiments in the kestrel (Falco tinnunculus)

We studied the limiting factors for brood size in the kestrel, Falco tinnunculus, by measuring parental effort in natural broods of different size and parental response to manipulation of food satiation of the brood. Parental effort was quantified as total daily time spent in flight, and total daily energy expenditure, from all‐day observations.

Estimation of daily energy expenditure from heart rate and doubly labeled water in exercising geese

We investigated whether daily O₂ consumption (V̇o2) could be predicted from heart rate (fH) in five exercising barnacle geese (Branta leucopsis) and compared the accuracy of this method with that of the doubly labeled water (DLW) method. The regressions of V̇o2 on fH, based on incremental speed tests, differed among individual birds. The O₂ pulse (i. e., V̇o2/fH) progressively increased with exercise level from 0.22 mL O₂ heartbeat⁻¹ during resting to an estimated 0.47 mL O₂ heartbeat⁻¹ during flight. Daily V̇o2, was generally underestimated (-3.9%) by (individual) resting O₂, pulses but overestimated (+8.4%) by linear regressions of V̇o2 on fH. However, it was wellpredicted (+0.8%) by the O₂ pulses appropriate for each exercise level When using relationships derived from the group of birds, the estimations were generally improved (-3.3% for resting O₂, pulse, -0.03% for appropriate O₂ pulse) but poorer (+13.6%) for the group linear regression. Some of these predictions were better than the estimation of daily CO₂ production (V̇o2) by the two-compartment model of the DLW method (average algebraic error of +0.9%). We conclude that fH can be used to estimate daily energy expenditure in birds accuratelyprovided that (1) its application is limited to the range of exercise levels in which fH has been calibrated against V̇o2 and (2a) V̇o2-fH relationships are determined for each individual bird or (2b) the fH measurements of several free-ranging birds are averaged. Heart rate can also be used to indicate within-day variation in energy expenditure.

Time allocation in the kestrel (Falco tinnunculus), and the principle of energy minimization

(1) Time allocation of the kestrel in the Netherlands was established by dawn to dusk observation of focal birds. Time budgets were analysed with respect to time of year, phase of the breeding cycle, sex and weather conditions. (2) The common vole, Microtus arvalis L., was the major food source (92% of food items caught) with minor additions, especially in summer, of common shrews, Sorex araneus L., songbirds and juvenile waders. (3) Flight-hunting and perching were the two main foraging modes. Flight-hunting yielded, on average, 2.2 small mammals h-1 in winter and 4.7 in summer. Perching yield dropped from 0.3 mammals h-1 in winter to below 0.1 in summer. Flight-hunting yield reflected seasonal variations in food availability, perching yield did not. (4) There was no stage in the annual cycle where available daylight limited the daily flight-hunting time. There were no weather conditions where daily flight-hunting exceeded an average of 3.6 h or 20% of the active day. Stringent periods, in the sense that all buffer time is used for foraging, were found neither in winter, when food was scarce, nor in summer when food demand was highest. (5) Experimentally increased hunger of the brood led to increased male parental effort in terms of time spent flight-hunting plus flying, with a recorded maximum of 60% of the active day. Flight-hunting yield did not increase. (6) In winter, kestrels minimized energy expenditure, not foraging time, by using the low-cost low-profit technique of perch-hunting. In summer they maximized daily energy gain within limits probably set by their rate of food assimilation.

Basal metabolic rate in relation to body composition and daily energy expenditure in the field vole, Microtus agrestis

Basal metabolic rate in the field vole (Microtus agrestis) was studied in relation to body composition and daily energy expenditure in the field. Daily energy expenditure was measured by means of doubly labelled water (D218O). In the same individuals, basal metabolic rate was subsequently derived from O₂ consumption in an open-circuit system in the laboratory. Body composition was obtained by dissecting the animals and determining fresh, dry, and lean dry mass of different organs. Daily energy expenditure for free-living field voles ranged from 1.8 to 4.5 times basal metabolic rate, with an average of 2.9 times basal metabolic rate. Variation in both daily energy expenditure and basal metabolic rate was best explained by body mass. Gender or reproductive activity did not have significant additive effects. Daily energy expenditure and basal metabolic rate showed significant positive relationships to body mass with similar mass exponents of 0.493 and 0.526, respectively. Overall, there was a significant correlation between daily energy expenditure and basal metabolic rate, but the mass-independent residuals (deviations from the allometrically predicted values) did not correlate. Carcass analysis revealed that a number of organs were slightly better predictors for daily energy expenditure and basal metabolic rate than was fresh body mass. Mass-independent residuals of lean dry heart mass and basal metabolic rate were positively correlated, which is in agreement with the idea that basal metabolic rate reflects the size of metabolically active organs. The study does not provide support for an intraindividual association of basal metabolic rate with daily energy expenditure in the field.

ENERGY-REQUIREMENTS FOR MOLT IN THE KESTREL FALCO-TINNUNCULUS

We estimated energy requirements for plumage replacement in the kestrel (Falco tinnunculus) by comparing O₂, consumption V̇o2 and metabolizable energy intake during molt and nonmolt. The energy expenditure for feather synthesis (S) as derived from the regression of basal metabolic rate (BMR) on molt intensity was 104 kJ·(g dry feathers)⁻¹. As derived from the regression of the resting metabolic rate of nonfasting birds at night (RMR) on molt intensity, S was 108 kJ·g⁻¹, and statistically indistinguishable from the BMR estimate. During the first part of molt the coefficient of temperature dependence of the standard metabolic rate below thermoneutrality (SMR) increased from 0.050 to 0.070 W·° C⁻¹. The metabolizable energy required for maintenance (Mm) increased with increasing body mass. The Mm in males was higher than in females of the same body mass. The Mm during molt was higher than during nonmolt episodes. The estimate for the cost of feather synthesis based on this difference was S = 117 kJ·g⁻¹. The cost of feather synthesis in the kestrel is thus much lower than values reported for three passerines (230-835 kJ·g⁻¹). This difference in efficiency may be related to diet (carnivorous vs. granivorous birds) or body mass.

Heat Increment of Feeding in the Kestrel, Falco tinnunculus, and its Natural Seasonal Variation

We measured the Heat Increment of Feeding (H) as the difference in oxygen consumption between the fed and fasting state in the kestrel at different ambient temperatures. Total H is a constant fraction of metabolizable energy intake and amounts to 16.6% of the energy assimilated. The effect of a meal was detected as elevation in metabolic rate lasting until 20 hours after the meal, independently of meal size. Below thermoneutral temperatures only part of H compensates for the cost of thermoregulation (T) up to a reallocation of 50% of H to T. Even at low temperatures (-12 °C) metabolic rate of fed kestrels is thus higher than that of fasting birds.

Energy Partitioning in Arctic Tern Chicks (Sterna paradisaea) and Possible Metabolic Adaptations in high Latitude Chicks

In order to survive and grow, neonates need to remain homeothermic. However, in the arctic, which is mostly regarded as a harsh environment with prevailing low ambient temperatures, achievement of homeothermy for chicks might cause problems. The small neonates have, besides an unfavorable volume area ratio, a less well developed plumage than adult birds. Therefore one might hypothesize that if no special cold adaptations have evolved, total energy expenditure of free living chicks is dominated by the costs of thermoregulation. Many physiologists working in extreme environments have focused on the ability of chicks to cope with low environmental temperatures (e. g. Maher, 1964; Norton, 1973; Aulie and Steen, 1976; Boggs et al., 1977; Pedersen and Steen, 1979; Bech et al., 1984; Jorgensen and Blix, 1985; Taylor, 1985; Boersma, 1986). However, to evaluate the importance of any adaptation to cold one needs to measure the actual contribution of thermoregulatory expenses to the total requirements of free living chicks. So far precise quantifications of the thermoregulatory costs in free living chicks in polar environments are only available for arctic tern chicks (Sterna paradisaea), studied on Spitsbergen (79 °N, 12 °W; Klaassen et al., 1989a,b), which are summarized here, after an analysis of possible metabolic adaptations in chicks to climatic conditions in general.