Question

Which one of the following is a flightless bird?
A.Emu
B.Kiwi
C.Ostrich
D.All of the above

Answer 1

Hint: Flightless birds are usually birds with primordial wings or heavy weight.
Flightless birds are birds that lost the ability to fly through evolution. There are over 60 extinct species, including the familiar ratites and penguins. The smallest flightless bird is the inaccessible island rail. The largest flightless bird is the ostrich which is also the largest living bird.

Complete step by step answer:
The following are some factors that facilitate the flight ability of birds.
-Hollow bones are filled with air to reduce its density, these are also known as pneumatic bones.
-Well-developed chest muscles give strength to the wings.
-Streamline body that reduces air friction and enables easy motion/ flight.
-Light feathers on the dorsum, long feathers on the wings, and tufted feathers on the tail to maintain balance and the center of mass
-The emu is the second-largest living bird in terms of height, after its ratite relative, the ostrich. It is endemic to Australia and Tasmania where it is the largest native bird and the only extant member of the genus Dromaius. It is farmed extensively worldwide for its eggs and meat.
-Kiwis are flightless birds endemic to New Zealand. It is approximately the size of a domestic chicken; kiwis are by far the smallest living ratites. They lay eggs that are half the weight of itself.
-The common ostrich is a species of large flightless bird native to certain large areas of Africa. It is one of two extant species of ostriches. They are the only living members of the genus Struthio in the ratite order of birds.

Hence option D is correct.

Note:
Ratites are any of the mostly large flightless birds with a ratite breastbone. They include the ostrich, rhea, emu, cassowary, and kiwi, together with the extinct moa, and elephant bird
Dodo was also a flightless bird, but it had the ability to fly for short distances for defense.