Energetics of Rewarming a Clutch in Starlings (Sturnus vulgaris)

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Abstract
Oxygen consumption in incubating starlings during the rewarming of a clutch was measured. The energy cost of rewarming the eggs increased with increasing length of the preceding inattentive periods and lower ambient temperature but not with clutch size. The contradiction between the measured costs of rewarming and those predicted from a heat-capacity model suggests a regulation of the blood flow in the brood patch independent of clutch size. Furthermore, a clutch size of six eggs seems to be optimal with respect to the cost of rewarming per egg. The question is raised of how much energy has to be produced exclusively for rewarming under natural conditions. It is suggested that, during inattentive periods (flight, foraging), energy is stored, and during rewarming it is channeled to the eggs. Consequently, no extra cost for rewarming may be necessary.