Whole populations of animals are now forced to travel great distances in pursuit of food and warmth. 300,000 Baikal teal （贝加尔湖水鸭） gather to escape from the Siberian winter by migrating south to Korea - the world's entire population in a single flock. But there are parts of the world that have no seasons. In the tropics the sun's rays strike the earth head on and their strength is more or less constant all year round. That is why the jungle grows so vigorously and supports so much life.
This forest covers only 3 percent of the planet's surface, but it contains more than 50 percent of all its plants and animals. The canopy is particularly rich. There are monkeys, birds and millions of species of insects, exactly how many we have no idea. The character of the forest changes as we descend, becoming ever darker and damper, favoring different kinds of animals and plants.
Less than 2 percent of the sunlight reaches the floor, but even here there is extraordinary variety. In the great island of New Guinea there are 42 different species of birds of paradise （极乐鸟）, each more bizarre than the last. This forest is so rich that nourishing food can be gathered very quickly. That leaves the male six-plumed bird of paradise with time to concentrate on other matters like tidying up his display area.