Cooperative breeding is a mystery that scientists have spent decades trying to unravel. It occurs among not only birds but also mammals, fish, and even insects. It is not necessarily a mating system per se, but has more to do with how adults care for their young. Cooperative breeding is distributed unevenly among taxonomic groups of birds. It appears to have been a part of some species’ evolutionary history from the beginning, but in other species it seems to have evolved over time. Its occurrence is not predictable in species or individuals. Its causes are difficult to identify. There is a dizzying number of variations on what cooperative breeding looks like from one species to the next.
Bald Eagle nest video cameras have provided an opportunity for viewers to observe and document 2 instances of cooperative breeding: on Catalina Island from 1992-2007, and near Lock & Dam 13 on the Mississippi River from 2014 through the present (spring 2019). Published literature includes 6 additional reports of cooperative breeding at Bald Eagle nests, in Alaska, Minnesota, Connecticut, New York, Texas, and British Columbia.
On the following pages I attempt to make sense of some of the mysteries of cooperative breeding and explore the behavior among raptors, including descriptions of each of the known cases of cooperative breeding among Bald Eagles: