Magnetic fields: One possible theory is that birds utilize Earth’s magnetic field to determine their latitude and longitude. Certain proteins—most likely in the eyes—may act like tiny compasses allowing birds to determine which direction is north or south.
Magnetoreception: Magnetoreception is a sense birds and some other animals have that allows them to sense and respond to magnetic fields. Birds may have compass cells, composed of magnetite crystals, in their beaks or eyes which, when interacting with Earth’s magnetic fields, can be used to detect direction and perhaps distance.
Sun: Birds may also rely on the sun to provide them with information about their latitude and longitude. The rising and setting of the sun in different locations creates a “map” of the world, which can be used to navigate their course.
Stars: Birds can use the stars as a form of celestial navigation to get information about their latitude and longitude. Different stars appear in different positions throughout the year, so birds can orient themselves relative to the stars and use this as a guide for migration.
Landmarks: Birds may use landmarks, such as the shape of coastlines, mountains and other terrain features, to help them navigate. Birds can use this information to get a general idea about where they are in the world and how to get to their destination.
It’s likely that birds integrate all of these different cues to successfully migrate, with different species using different strategies to make sense of their position and direction of flight.
