There are over 10,000 species of bird worldwide and on every continent.

Birds are classified as Aves or Neornithes and are known as avian dinosaurs.

Birds are important to humans for economic, religious and cultural reasons.

The largest of these animals is part of the flightless family and in the order of Stuthioniformes, which includes kiwis, emus, rheas and cassowaries.

This bird also lays the largest of all avian eggs, although there were other birds with larger eggs which are now extinct.

Which bird is the largest in the world?

The ostrich.

These huge, flightless birds can weigh up to 145 kilograms (320 lbs) and can stand over 9 feet tall. With their height and extremely large eyes they can see predators from a great distance and they can also outrun most of their predators. These birds have evolved to tolerate a large range of temperatures and living conditions.

Ostrich Subspecies:

North African ostrich

South African ostrich

Masai ostrich

Arabian ostrich (extinct)

Somali ostrich

Sources:

http://www.ucmp.berkeley.edu/diapsids/avians.html