Some species of birds are flightless because they are too heavy, and/or their wings are too small.
Birds become flightless due to their environment. Flying requires a lot of energy, so if there is no need to fly, they won't. For example, lack of predators or lack of trees means these birds don't need to fly as much. Over time, they will lose their flight ability altogether.
For example, penguins live in Antarctica. There are no trees there to perch on, and there are also no land predators. Instead penguins became adapted to swimming in the seas where there is food. Their wings then became more like flippers for swimming, and they became fatter to keep warm.
Ostriches and emus live in grasslands where there are few trees, so the birds have to stick to the ground. If they don't want to be eaten by predators they have to develop another way to move, so ostriches and emus became adapted for running quickly rather than flying.
Many Flightless Birds belong to the group known as ratites. Other ratites include the Southern cassowary of Australia and New Guinea, the kiwi from New Zealand, the ostrich from Africa and the rhea from South America. The reason these birds are flightless is that ratites have wings but the bones in their chests do not have the capacity for flight muscles, which is what a bird needs to fly. Although the emu does not actually weigh as much as it appears (30-45kg), its wings are also too small by comparison to lift it.
As the ostrich has always had natural predators (feline genus) it is unlikely although not impossible that they lost the ability of flight through dis-use. It is probable that they were simply designed and created flightless.
They are still considered birds because they have feathers, beaks and many other bird characteristics.
they haven't been flightless long enough to have their wings evolve into something else
Birds are not naturally featherless. If you see a featherless bird, either it is a genetic disorder, has been genetically altered, or simply has been plucked very recently.
No. Some flightless birds such as the kiwi have very small, rudimentary wings. Other flightless birds such as the ostrich have larger wings, but they are still small and quite useless for flight.
Yes. All birds have wings, even the flightless ones.
Yes. Takahe are birds, and all birds have wings. Even flightless birds have wings, though they are of little or no use.
their wings are not used for flapping
Flightless birds have a small keel and wings.
they can't fly, they are large and they have no wings, obviously! flightless birds include: ostrich, cassowary, emu and penguins!
Because their wings are atrophied.
All birds have wings: even flightless birds have wings, though they may be useless for flight. All birds also have legs.
Yes, penguins are birds. They are flightless but they have beaks, wings, are covered in feathers and lay eggs.
They do not need to flap their wings.
yes it is. The kiwi's closest relatives were the other New Zealand ratites, the Moa which was another flightless bird.
Most birds use their wings for flight. Some of the flightless birds, or birds which do not fly much, may use their wings just for balance, especially when perching (e.g. chickens). For some flightless birds such as the kiwi, their wings appear to be without purpose.