The ostrich is the biggest bird in the world with a male ostrich often growing more than 2 metres tall. The ostrich is also the world's fastest bird on the ground being able to run at speeds of up to 50 mph for short periods of time.Despite the fact that the ostrich is a bird, the ostrich cannot fly and instead will run away when threatened. The ostrich weighs more than 100kg which is the main reason as to why the ostrich is unable to fly. The ostrich will also lay flat on the ground to hide from predators.
Contrary to popular belief, ostriches do not bury their heads in sand. This myth likely began with Pliny the Elder (AD 23–79), who wrote that ostriches "imagine, when they have thrust their head and neck into a bush, that the whole of their body is concealed." This may have been a misunderstanding of their sticking their heads in the sand to swallow sand and pebbles, or, as National Geographic suggests, of the defensive behavior of lying low, so that they may appear from a distance to have their head buried.