The Ostrich is the world's largest bird. Although it cannot fly, it can run at high-speeds. In fact, it is the fastest creature on two legs. Powerful legs, flexible knees and supple, two-toed feet are its adaptations for sprints of up 70km/hour and long distance running. Ostriches live in small fewer than a dozen birds, led by a dominant male. The male ostrich has soft, curling plumes. Female birds are slightly smaller in size and have brownish plumage and off-white wings and tails. Juveniles are greyish-brown.