Ostrich

The ostrich is the biggest bird still alive and the largest member of the ratite suborder Palaeognathae. They are among the birds that cannot fly due to their enormous size and feeble wings. The ostrich reportedly lost its ability to fly a very, very long time ago when its ancestors decided to take advantage of the vast, empty landscape that had been left behind following the extinction of the dinosaurs. Eventually, flying birds gave up flight in favor of speed after learning to forage on the ground. The ostrich is actually quite adept at this; when necessary, it can run at speeds of up to 43 mph and, when out for a leisurely jog, can maintain a steady pace of around 31 mph.

The ostrich and other birds with similar characteristics actually found flight loss to be a remarkably effective tactic. According to Genetic research, ratites (emus, kiwis, and rheas) developed this ability three times, and the ostrich's flying ancestor was specific to its species.