The Energetic Consequences of Incubation for Two Passerine Species

A previously developed model of heat transfer in incubating birds is applied to data describing the microclimate and nest/clutch/parent complex of the Red-winged Blackbird (Agelaius phoeniceus) and the Willow Flycatcher (Empidonax traillii) in southeastern Washington.Over an average 24-h cycle, the resting energy expenditure of an incubating female in both species averages 16-18% below that of a female perching on top of the vegetative canopy near the nest.This reduced energy requirement for incubating birds results from both the insulation of the nest and microclimatic amelioration associated with the nest's location.Accounting for the heat required to raise egg temperatures after parental inattentive periods lessens, but does not eliminate, this reduction in resting energy expenditure in incubating compared to nonincubating adults.