Most of them seem to require mathematical computations that most humans would find challenging. In fact, scientists still have a long way to go before they understand completely how birds navigate. But some parts of the picture have started to fall into place. The evidence seems to suggest that birds use a combination of different methods. Let's look at the various possibilities in turn.
Many animals learn to recognize their surroundings to determine their route.
They remember the shape of mountain ridges, coastlines, or other topographic features on their route, where the rivers and streams lie, and any prominent objects that point to their destination. For example, a digger wasp always memorizes the land marks around its burrow. Birds may use this method to locate their nest, but it seems unlikely that it will support flights over long distances. And it clearly cannot be used for navigating over large bodies of water or for flying at night, both of which many species of birds do every year. Of, course, navigating by recognizing the terrain does not seem to require much by way of mathematics.