Published: 2 September, 2004

Penguin can 'fly,' only in water

Why can birds fly but penguins can't?

Of all animals, birds are perhaps best known for their ability to fly, but many kinds of birds are flightless. Penguins belong to a group called Sphenisciformes, in which all species are flightless and aquatic. Another group of flightless birds is known as the ratites. It includes the ostriches of Africa, rheas of South America, emus of Australia, cassowaries of New Guinea and Australia, moas (now extinct) and kiwis in Australia, and elephant birds of Madagascar (an extinct group that includes the largest birds ever known). Other flightless birds include a species of cormorant in the Galapagos, a grebe in the Andes, a parrot in New Zealand, and several species of pigeons on islands in the South Pacific and Indian Oceans.

The anatomy and brain structure of flightless birds indicate that they all descended from ancestors that could fly. In many cases, flightless birds inhabit islands where there are no predators. Without the energetically costly need to take flight from predators, many of these birds have become more specialized for a lifestyle on the ground or in the water and completely lost their ability to fly.

Many kinds of diving birds such as loons, auks, and various ducks, are able to fly but are also well adapted to their almost entirely aquatic existence. Their legs are positioned far back on the body for more efficient paddling, but they can also use their wings for extra power and control when diving and swimming under water.

Penguins have some of the same characteristics of many diving birds, but they have evolved additional features that reflect their highly aquatic lifestyle, such as the reduction and fusion of the wing bones into paddle-like flippers. Also, rather than having hollow bones as flying birds do, penguins have solid heavy bones that function as ballast (weight) for more efficient diving. Furthermore, penguins actually use their wings for moving under water much like any other bird does to move through the air; such that many people remark that penguins appear to be "flying" through the water.