Written by Bryan Watts
July 11, 2010
For bald eagles (Haliaeetus leucocephalus), brood size typically varies between one and three and geographic patterns in both average brood size and proportion of three-chick broods are believed to vary with prey abundance. Bald eagle broods hatch asynchronously, often form dominance hierarchies, and may exhibit brood reduction depending on prey availability. Under normal circumstances, the degree of hatching asynchrony for unusually large clutches likely creates such a disadvantage for the last chick that it sets an upper bound on brood size. Although four and five-egg clutches have been reported with some regularity in bald eagles, the successful fledging of a four-chick brood is extraordinarily rare. A four-chick brood was banded in the upper Chesapeake Bay in 1986, but fledging success was never confirmed.
In early April of 2009, John and Yoke DiGiorgio, long time conservationists and friends of the Center (see their website http://www.naturesartllc.com) discovered a four-chick brood along the Delaware River just south of the Hamlet of Portland, PA. They would make careful observations of this nest on 55 days until well after the chicks had fledged. They noted behavioral interactions of the chicks, prey delivery by the adults, and feeding activities. They also filmed the brood and are editing a video documenting their development.