A species of warbler summers in Germany, where the young are raised. At the close of the season the parent birds depart for the headwaters of the Nile in Africa, leaving behind the young birds, which are not yet ready for the long flight. A few weeks later the young birds take off and fly to Africa, traveling thousands of miles without a guide over a path they have never seen, to join their parents. German scientists proved that they navigate by the stars. These birds are hatched from the egg with this ability and with much of the pre-programmed navigation and flight instructions already in their little bird brains.
More recent research reveals that a pigeon has two independent mechanisms for determining direction.
In sunny weather the pigeon tells direction by means of the sun, but in cloudy weather it tells direction by means of some kind of magnetic compass located somewhere in its head. The common pigeon guards an even more mysterious secret of navigation. It has knowledge of a map which it reads as it travels to its destination. This map is entirely independent of surface features on the earth, yet is strangely influenced by the geographical location in which the bird finds itself. Scientists at Cornell University and other research centers have continued the effort to learn the pigeon's secret.