Daily Energy Expenditure and Water-Turnover Rate of Adult European Starlings (Sturnus vulgaris) during the Nesting Cycle

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Abstract
We measured rates of carbon-dioxide production and water turnover in adult starlings by the doubly-labeled water technique. CO2 production of females was 4.23 cm3·g−1·h−1 during the incubation period, 4.86 cm3·g−1·h−1 during the early part of the nestling period, and 6.86 cm3·g−1·h−1 during the middle of the nestling period, the time of greatest food requirement by the brood. During the last period, the rate of CO2 production by males was 5.50 cm3·g−1·h−1. CO2 production was independent of brood size (3-7, approximately a two-fold range of brood mass) during both the early and middle parts of the nestling period. Water-turnover rates paralleled CO2 production over the nesting cycle, the average values for each sample varying between 0.048 and 0.070 per h. Within each of the samples, water-turnover rates were independent of CO2 production but appeared to be influenced by weather conditions. During the middle of the nestling period, water-turnover rates were higher on 2 cold, rainy days than on 2 milder days. The maximum daily energy expenditure for females was about four times predicted BMR, similar to values reported in other studies.