Read the following text and answer the questions that follow
Most people think of birds as animals that fly. Scientists, however, do not define birds as animals that fly, because some birds do not. Of the 10,000 or so species of birds, 46 cannot fly. Flight plays a key role in survival for most birds. It allows them to find food over a wide area and to get away from predators. Ancestors of flightless birds may have lost their ability to fly because they had no regular predators or did not need to fly to find food. Rather than fly, some of these birds developed other traits to catch food and avoid enemies. Two examples of lightless birds are penguins and ostriches.
Penguins are sea birds with flipperlike wings, dense feathers, and thick bodies. Unlike birds that fly, penguins do not have wide wings, large feathers, or hollow bones. In order to catch fish they feed on, penguins use their powerful wings to swim swiftly. When they swim, they look as if they are flying through the water. Their bodies enable them to dive deep underwater, and their dense feathers protect them from the cold. Their swimming skill also helps them to escape predators.
Ostriches are members of a group of birds called ratites. They are known for their long legs, long necks, and large size. To protect themselves, ostriches stay in groups and use their excellent vision and hearing to notice enemies. When danger approaches, they can run at speeds of more than 65 kilometers per hour to escape. In addition to using their strong legs to run with, ostriches can deliver powerful kicks. The strong, heavy bones that enable them to run well also make them too heavy to fly.
Not all flightless birds have been successful in protecting themselves. Flightless birds on some islands had no enemies until people arrived. These birds were hunted and easily caught by people and the animals brought about by people. Human land development has destroyed the habitats of some birds. A number of flightless birds – such as the dodo and the great auk- became extinct because they were unable to adapt to new conditions and new enemies. Today, the kakapo parrot and the takahe of New Zealand are near extinction as well. After millions of years of survival, these flightless birds have had their populations reduced to a few dozen.