<P> 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 . </P>
<P> 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 . </P>
why are birds such as kiwi and penguin unable to fly
why are birds such as kiwi and penguin unable to fly
through evolution
through evolution