The Largest and Smallest Birds

　　The species of birds are only second to those of fish among all vertebrates. There are 9021 species of birds in the world today. China is one of the countries that have the most species of birds and we have 1260 species of birds according to our records altogether. Birds vary a lot and their sizes are quite different too. The African ostrich, which is good at running, is as high as 2.7 m and weighs more than 150 kg. It can run at a speed of 60 kilometers per hour. African ostrich is the giant among all birds. In contrast, the hummingbird of Cuba, which is good at sucking honey from flower, is less than 6 cm in length and weighs only 3 to 5 g. Its size is like that of a bee and it is the smallest bird among all.