There are about 9，703 kinds of birds divided up into 23 orders，142 families and 2，057 genera（属，种类）.The total number of birds on the planet is very difficult to estimate because their populations fluctuate seasonally，but scientists have suggested that there may be between 100，000 and 200，000 million adult or near adult birds on the planet at any one time.
    The most common bird in the world is Red Junglefowl most regularly seen as the common domestic（家养的） chicken.The most widespread commonly seen wild bird in the world is probably the European House Sparrow which has been transported all over the world by European settlers and can now be found on 2/3 of the land masses of the world including New Zealand，Australia，North America，India and of course Europe.
    The largest living bird is without doubt the ostrich.This ever-popular bird stands a magnificent 2.74 m and can weigh as much as 160 kg.
    The heaviest flying bird is the Kori Bustard of Africa.A number of specimens have been scientifically recorded weighing 19 kg and heavier specimens have been reported but not confirmed.Close runner-ups are the Eurasian Bustard and the Mute Swan，both of which have been recorded at 18 kg.

（1）How many kinds of birds are there in the world？

There are about 9，703 kinds of birds.

There are about 9，703 kinds of birds.

（2）What's the largest bird in the world？

The ostrich.

The ostrich.

（3）Where can people find the most common birds？

They can be found in 2/3 land masses of the world，including New Zealand，Australia，North America，India and of course Europe.

They can be found in 2/3 land masses of the world，including New Zealand，Australia，North America，India and of course Europe.