ALL these species have one common peculiarity: they wrap their eggs for warmth in fox- or hare-skins, which they have chanced to find or have stripped from the animals themselves; afterwards they replace the eggs in their nests to be hatched out by the generous heat of the sun. 1 They are unable to remain constantly sitting on the eggs in the nest, since this makes their claws grow too curved and so ineffective for grasping prey. 2 However, they show the utmost concern for rearing their young in the way they bring back fish, birds, and hares for them to eat.