When men set off on a journey, they take a map with them. Sailors, who do not have roads or sign-posts laid out for them, have to take their bearings with instruments like the sextant and the compass, and with long and complicated calculations. As a result of this they can arrive at their destination, and find their way back to the home port.
The little garden warbler, which leaves the northern hemisphere to spend the winter in South Africa (it thus has the benefit from two hot seasons every year), can, without sextants, compasses, maps or calculations, find its way back to the garden it lived in during the previous spring.
Can scientists discover the secrets of migration?
Everything possible has been tried on the warbler-and many other migrants-in an attempt to discover their secret!
Since it flies at night probably, like sailors, it can navigate by the stars. All the experiments that have been possible have confirmed this.
At the navigation school in Bremen, in an enormous planetarium normally used for training navigators, the warblers were subjected to orientation tests that would have driven the trainee-officers mad: this included rapid changes in the positions of stars, and the complete inversion of the 'vault of heaven'. They always found their migratory route faultlessly, except when the stars were 'switched off'.
Of course, warblers cannot 'take their bearings'. But they do seem to have a kind of sixth sense which uses the stars as landmarks. Other, daytime migrators use the Sun. And they take their bearings as easily and automatically as we can tell the top of a mountain from the bottom. Their brains have the same faculties of sight and hearing as we do.