Can Ostriches Fly? Why the Biggest Bird Stays on the Ground

Why can’t ostriches fly?

Several features of the ostrich body make flight impossible:

• Weight. Flying gets harder as a bird gets heavier, because body weight grows faster than wing area. The heaviest flying birds today, the great and kori bustards, top out at around 20 kg (44 lb). A male ostrich weighs about five to six times more.
• No keel. Flying birds have a tall ridge on the breastbone, called the keel, that anchors the big flight muscles. The ostrich breastbone is flat, like a raft. That is where the name of its group, the ratites, comes from: ratis is Latin for raft.
• Soft feathers. In a flying bird, tiny hooks on each feather lock the vanes into a stiff, airtight surface. Ostrich feathers lack these hooks, so they are soft and fluffy. They make good insulation and display plumes but cannot push against the air.
• Small wings for the body. An ostrich’s wingspan is about 2 m (6 ft 7 in), similar to many large flying birds, but it has to serve a body many times heavier.

In short, natural selection shaped the ostrich into a long-legged runner. Its leg muscles are enormous, and much of the strength a flying bird puts into its breast went into the thighs instead.

What do ostriches use their wings for?

Ostrich wings are not useless. They have several jobs:

• Steering and braking. Tests on running ostriches show that the birds spread their wings to keep their balance when they brake, turn sharply or zigzag away from a predator.
• Display. Males court females by crouching and waving their black-and-white wings in turn, and both sexes use the wings in threat displays.
• Temperature control. Ostriches can cover the bare skin of their thighs with their wings to keep warm on cold nights, or lift the wings to let heat escape on hot days.
• Shade and shelter. Parents spread their wings over eggs and small chicks to shade them from the sun.

The wings also end in two small claws, a reminder of the ostrich’s reptile-like ancestry.

How did ostriches lose the ability to fly?

Ostriches belong to an ancient bird group called the palaeognaths, which also includes the emus, cassowaries, rheas, kiwis and the extinct moa and elephant birds. For a long time scientists thought these birds were descended from a single flightless ancestor that spread across the old southern supercontinent of Gondwana before it broke apart.

DNA studies changed that picture. The tinamous of Central and South America belong to the same group, and they can fly. Genetic family trees place tinamous inside the ratite group rather than outside it, and show that the closest living relatives of the extinct elephant birds of Madagascar are New Zealand’s kiwis. The most likely explanation is that flying ancestors spread around the world and that flightlessness evolved several separate times, on different landmasses.

Fossils support this. Early palaeognaths called lithornithids, which lived in North America and Europe more than 50 million years ago, had the build of small flying birds. Once ancestors of the ostrich lived on the ground in open country, a big body and long legs paid off better than costly flight muscles.

Is the ostrich the only bird that cannot fly?

No. More than 60 living bird species cannot fly. Besides the ostrich and Somali ostrich, the big flightless runners include the emu of Australia, the cassowaries of Australia and New Guinea, and the two rheas of South America. Kiwis, penguins, the kakapo parrot and a number of island rails cannot fly either. The full roundup is in flightless birds.

Flightless birds tend to evolve in two situations: on islands with no ground predators, where flying is no longer needed, and in open country where running fast is the better escape. The ostrich is the second kind, and it is so good at running that it can reach about 70 km/h (43 mph). For how it compares with its nearest look-alike, see emu vs ostrich.

Myths about ostriches and flight

Myth: ostriches “fly” a short way when they run. Ostriches never leave the ground for more than the moment between strides. A running ostrich holds its wings out, which can look like an attempt to take off, but the wings are only helping it balance and turn.

Fact: a big wingspan does not mean a bird can fly. An ostrich’s wings span about as far as those of a large eagle, but what matters is the load each square meter of wing must carry and the power of the flight muscles. On both counts the ostrich falls far short.