The ostrich is too big to fly but has become so perfectly adapted to high-speed running that it is the fastest creature on two legs. At speeds of up to 70 km/h (44 mph), it can easily outstrip most enemies. Powerful legs, flexible knees and supple, two-toed feet are its adaptations for speed. The ostrich has lost its strong wing feathers, but the male has soft, curling plumes, once much in demand for fashionable hats and boas. Female birds are slightly smaller than males and have brownish plumage and off-white wings and tails. Juveniles are grayish-brown. Ostriches eat mostly plant matter but occasionally feed on small reptiles.  They are nomadic, wandering in small groups in search of food. At breeding time, the male collects a harem of 2 to 5 females. One female scrapes a shallow pit in the ground in which to lay her eggs, and the rest of the harem probably uses the same nest. The eggs are the biggest laid by any bird -- the equivalent in volume of about 40 hen's eggs. The male bird takes over the incubation of the eggs at night and shares in the care of the young.