Thousands of species of birds are known to live throughout the world. Some make their home in aeries high in the mountains; many others fly from tree to tree in temperate or tropical forests; and still others glide above shifting desert sand dunes. Then there are the birds, such as ostriches and penguins, which do not fly but instead run across land or swim in the oceans. The Encyclopaedia of Birds details various aspects of these amazing creatures' lives and provides insight into humans' fascination, and complicated relationship, with birds of all kinds.