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Field Metabolism and Food Consumption of Savannah Sparrows during the Breeding Season

Joseph B. Williams
The Auk
Vol. 104, No. 2 (Apr., 1987), pp. 277-289
Stable URL: http://www.jstor.org/stable/4087034
Page Count: 13
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Field Metabolism and Food Consumption of Savannah Sparrows during the Breeding Season
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Abstract

I applied the doubly labeled water (DLW) technique to measure rates of water flux and energy expenditure of Savannah Sparrows (Passerculus sandwichensis) during two breeding seasons on Kent Island, New Brunswick, Canada. Simultaneous to DLW measurements, I constructed time-activity budgets for territorial males, monitored nest attentiveness for incubating females, and quantified frequency of nest visitation for parents feeding young. To ascertain the relationship between brood size and adult energy expenditure, I measured the energy expenditure of adults feeding 2, 4, and 6 nestlings. There was little difference in field metabolic rates (FMR) between territorial males $[161.0\pm 21.7\ ({\rm SD})\ {\rm ml}\ {\rm CO}_{2}/{\rm h}]$ and males that fed 4 nestlings $(157.6\pm 19.7\ {\rm ml}\ {\rm CO}_{2}/{\rm h})$. Incubating females expired CO2 at rates lower than males during the same time period (134.4 ± 7.9 vs. $161.0\pm 21.7\ {\rm ml}\ {\rm CO}_{2}/{\rm h}$ but similar to rates for females feeding 4 young, the normal brood size ($134.4\pm 7.9\ {\rm ml}\ {\rm CO}_{2}/{\rm h}$ for incubating females vs. $136.5\pm 26.9\ {\rm ml}\ {\rm CO}_{2}/{\rm h}$ for females feeding young). Incubating females expended energy at a lower rate than females making 8 or more trips to the nest per hour, the average feeding rate for females late in the nestling period. For males and females together, water influx and efflux rates averaged 17.1 ± 3.2 and $17.2\pm 3.0\ {\rm ml}\ {\rm H}_{2}{\rm O}/\text{day}$, suggesting that birds balanced water intake against water losses. Mean daily solar radiation (MDSR; W/ m2) also influenced FMR during the nestling period. The equation ml ${\rm CO}_{2}/{\rm h}=172.6-0.07$ (MDSR) described the relationship. When brood sizes were manipulated, parents responded by altering their frequency of nest visitation; as frequency increased, so did the FMR of females but not of males. The equation ml ${\rm CO}_{2}/{\rm h}=98.4+5.3$ (mean visits/h) described the relationship. Construction of a food budget indicated that, on average, territorial males consumed 21.1 g fresh arthropods per day, while incubating females ingested 17.5 g/day or 210.0 g during the 12-day incubation period. Through the 8-day nestling period, males augmented their foraging by 75%, females by 87%, to feed a brood of 4.

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