The advance of the seasons brings constant change. As the sun’s influence diminishes in the north, so the deciduous forests of America begin to shut down, losing their leaves in preparation for the dark, cold months ahead. One season hands over to another. Some organisms thrive on decay. But this must make special preparations for winter and a

life with little sun. Whole populations of animals are now forced to travel great distances in pursuit of food and warmth. Three hundred thousand Baikal teal 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 three percent of the planet’s surface but it contains more than fifty percent of all its plants and animals. The canopy is particularly rich. There are monkeys, birds and millions of species and insects, exactly how many we have no idea.