Factors influencing the growth of Bald Eagles in north central Saskatchewan

Abstract

Mass and eighth primary growth of nestling Bald Eagles (Haliaeetus leucocephalus) were studied in north central Saskatchewan from 1980 to 1982. There were no significant differences among years for any measure of growth. Clutch size and the relative timing of hatching within each breeding season also had no effect on growth. In broods of two young, second-hatched chicks (C2) grew slower than first-hatched chicks (C1) if the hatching interval between siblings was 2 days rather than 1 day. As both hatching asynchrony and the degree of suppressed growth of C2 were independent of absolute growth rates (and hence presumably food supply), it was unlikely that individual females modified the degree of asynchrony in any adaptive manner. Nestlings raised in an area predicted to have high fish (prey) productivity, given the morphology and chemistry of the lake, grew faster than chicks in an area of lower productivity. Growth rate was significantly correlated with the total mass of prey, but not the number of prey items, delivered to the nests by the parents.