Bioenergetics of Egg Production by Female House Sparrows

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Abstract
To determine the daily and total energy expenditures of breeding female House Sparrows (Passer domesticus), we collected 276 females near London, Ontario between April 1981 and May 1983. Protein and fat content of developing follicles, eggs, and oviducts were determined and converted into their energy equivalents. Eight days were required to develop and lay a modal clutch of 4 eggs. Fat energy requirements were not estimable accurately because total body fat did not decline linearly over the egg production period; therefore, energy requirements were estimated as a range. Based on a 4-egg clutch, the maximum daily costs of reproduction, 16.5-17.6 kJ/day, equalled 44-47% of a female's standard metabolic rate. We estimate that daily costs very less than 10% for other clutch sizes (3 or 5). The total energy demand of reproduction was 66-71 kJ. Protein requirements comprised 59-63% of the total costs and were apportioned among oviduct (5-6%), yolk protein (17-19%), and albumen (36-39%). Fat requirements accounted for the remaining 37-41% of total costs. Based on our estimates of energy needed for reproduction, and on other evidence, we suspect that egg production by House Sparrows is not constrained by energy acquisition.