There are about 9000 species of birds in about 170 families with 1 to 300 birds per family. Laying of eggs 4. This is primarily because birds are so easy to study in the field and harder to keep in the lab than other vertebrates. The set of birds in any defined area is called the avifauna . The diversity of the avifauna is dependent both the climate and vegetation structure, primarily.
Tropical forests have the highest bird species diversity and the tundra and open ocean the lowest.
The only place where there are no breeding birds is the center of Antarctica. The spatial distribution of birds is due to the adaptations of birds - they are adapted to particular habitats. The temporal distribution of the birds is essentially one of migration. Classically, migration is a north-south oriented movement between a breeding and wintering range.