This female bald eagle is both guarding the nest, and feeding her young with a fish recently supplied by her mate.  She uses great care when moving about the nest, balling up her feet to protect the fragile babies from her huge talons.

The term “sexual dimorphism” means that one sex will be bigger than the other.  This is a concept we easily accept in humans.  Men are generally larger than women.  But in raptors (eagles, hawks, falcons, owls), it is the female of the species that is larger than the male.  In bald eagles, the female can be up to 30% bigger than her mate.  There are various theories about why this should be so.  One is that the female spends more of the incubation and early days of the chicks on the nest, and is therefore a bigger adversary when the nest is threatened by danger.  A second is that both parents provide food for their growing brood, and by being of different sizes, they can take different sized prey- thereby spreading out the available prey base.  Seen together, the size difference is pretty obvious.