Time Budgets and Behavior of Nesting Bald

Time budgets for adult Bald Eagle (Haliaeetus leucocephalus) activities at nests were documented from mid-incubation to fledging at one nest and from hatching into the postfledging period at two nests. Time-lapse cameras recorded instantaneous samples of activity at 90 second intervals. Both sexes incubated eggs and brooded young. Eggs were incubated for 95% of daylight hours, with the female and male contributing 53% and 42% respectively. Total brooding time averaged 79% of each day 1-10 days after hatching and declined to 6% of each day 41-50 days after hatching. Both sexes delivered prey and the frequency of prey deliveries did not vary with the age or number of young in the nest. Females fed young 81-91% of the time and the number of feedings increased with the number of young in the nest. Weather variables had significant impact on nearly all nesting activities. Incubating and brooding rates increased with wind velocity and decreased with daily high temperature. Brooding rates also increased with daily precipitation and decreased with sunniness. Females tended to incubate and brood more and males less during periods of cold, wet, windy and cloudy weather. Prey delivery rates decreased with precipitation and feedings decreased with daily high temperature. Comparisons with other raptor species indicate that Bald Eagles share nesting duties between the sexes more than many birds of prey. Recommendations for minimizing human disturbance during the nesting cycle and the possible role of reversed sexual dimorphism in determining sex role differentiation are discussed.