Activity Budgets, Energy Expenditures, and Energy Intakes of Nesting Ferruginous Hawks

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Abstract
Daily energy expenditures of two pairs of nesting Ferruginous Hawks were estimated from activity budgets, and were compared with energy intakes determined from observed prey captures. In 1974 and 1975 respectively, the adult males expended 330.9 ± 37.8 (SD) and 374.3 ± 18.1 kcal/day, whereas the adult females expended 265.3 ± 28.3 and 294.6 ± 34.5 kcal/day. The total daily energy expenditures of adults and young (approximately 995.8 and 967.1 kcal/day in 1974 and 1975, respectively) were more than balanced by their gross intakes (1,337.8 ± 308.2 and 1,393.2 ± 236.7 kcal/day, respectively). The adult males had foraging efficiencies (kcal gathered/kcal expended in hunting) estimated at 7.56 ± 2.17 in the first year and 7.31 ± 1.80 in the second. Estimates of energy intake and foraging efficiency are maxima due to the likely under-representation of small prey items in regurgitated pellets.

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