Flightless bird Flightless bird Flightless birds are birds that through evolution lost the ability to fly. There are over 60 extant species including the well known ratites (ostrich, emu, cassowary, rhea and kiwi) and penguins. The smallest flightless bird is the Inaccessible Island rail (length 12.5 cm, weight 34.7 g). The largest (both heaviest and tallest) flightless bird, which is also the largest living bird, is the ostrich (2.7 m, 156 kg). Ostriches are farmed for their decorative feathers, meat and their skins, which are used to make leather. Many domesticated birds, such as the domestic chicken and domestic duck, have lost
The Life of Birds possibly show paths this evolution may have taken. One of the biggest birds to have ever existed was the terror bird, which proliferated after dinosaurs vanished and stood up to 2.5 metres tall. By comparison, the ostrich, while not closely related, is the largest and heaviest living bird. It was probably the evasion of predators that drove most birds into the air, so their flightless cousins evolved because they had few enemies. Accordingly, such species are more likely to be found on islands, and Attenborough visits New Zealand to observe its great variety, most especially the kiwi. Also depicted is