The year begins in the summer at the bird's breeding grounds, and migration takes place in the fall, when the weather starts to cool. The bird then flies to a warmer place to spend the winter, returning to the breeding grounds in the spring. Many bird species do not migrate at all, and even within a species, some groups may migrate and others may not. Populations that live in an area that has comfortable weather year-round may not need to migrate, for example. Birds are able to use the stars and sun to plot their course, and they are also able to work out time using an internal 24-hour clock.
Birds have to lay down a substantial food reserve to be able to fly thousands of miles.
They do this by accumulating a reserve of fat before the migration begins. Conservation It has been estimated that more than ten percent of all birds are threatened with extinction. Tropical rainforest is being lost at a rate of up to 25 million acres per year, and the populations of birds like pheasants, birds of prey, hornbills, toucans and parrots are at serious risk because of loss of rainforest habitat. Many bird species live in wetlands, or rely on wetlands as resting places during migration. Wetlands have long been considered 'wasteland', available for draining for agriculture or for construction projects, and the widespread drainage of wetlands has resulted in the decline of many species of waterbird.