Daily Energy Expenditure of Purple Martins (Progne Subis) During the Breeding Season: Estimates Using D2O(18) and Time Budget Methods

Abstract

Mean daily energy expenditures (DEE) determined from D_2O(18) turnover rates were 39.9 kcal (RQ=0.9) and 43.9 kcal (RQ=0.8) for two female purple martins feeding nestlings. The means for two males not feeding nestlings consistently were 31.2 kcal (RQ=0.9) to 34.2 kcal (RQ=0.8). Time budget observations obtained during the corresponding period of the breeding cycle at a second colony indicated females spent 67% of the active day in flight while males appeared to spend only 47% in flight. An equation for estimating daily energy expenditure from time budget data provide results that differ from the D_2O(18)derived DEE by 0.8% (RQ 0.8) to 9.9% (RQ 0.9) for females and 11.4% (RQ 0.8) to 19.1% (RQ 0.9) for males. The difference in apparent accuracy for the females and males is attributed to less adequate sampling of the male's behavioral activities. We advocate using time budget data for estimating daily energy expenditure when it is unfeasible to use the D_2O(18)method.