Not all species of birds are capable of flying. The best known
flightless birds are the ostrich, emu, cassowary, rhea and penguin.
Flightless birds evolved from flying ancestors; there are about
forty species in existence today. They lost the power of flight
because they had few enemies. Most flightless birds evolved in the
absence of predators, on islands. A notable exception, the ostrich,
which lives in the African savannas, has claws on its feet/birds
to use as a weapon against predators.
Two key differences between flying and flightless birds are the
smaller wing bones of flightless birds and the absent (or greatly
reduced) keel on their breastbone. The keel anchors muscles needed
for wing movement. Flightless birds also have more feathers than
New Zealand has more species of flightless birds (including the
kiwi, penguin, and takahe) than any other country. One reason is
that until the arrival of humans roughly 1000 years ago, there were
no land mammals in New Zealand other than three species of bat;
the main predators of flightless birds were larger birds.
With the introduction of mammals (among them humans) to the habitats
of flightless birds, many have become extinct, including the Great
Auk, the Dodo, and the Moa.
The smallest flightless bird is the Inaccessible Island Rail (12.5
cm and 34.7 g). The largest - heaviest and tallest - flightless
bird (and, incidentally, the largest living bird) is the ostrich
(2.7 m and 156 kg).
Flightless birds are the easiest to take care of in captitivity
because they do not have to be kept in cages. Ostriches used to
be farmed for their decorative feathers. Today they are raised for
their skins. Their skins are used to make leather.
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