Magnetic field navigation
The Earth generates a magnetic field that runs from the North Pole to the South Pole. Birds have evolved the ability to sense this magnetic field, which acts like an invisible compass. Scientists believe birds detect magnetism through either specialized cells in their eyes that react to magnetic fields or through magnetite crystals found in their beaks. This allows birds to know which direction is north or south, helping them stay on course during their long journeys.
Celestial navigation
Birds use the position of the sun and stars to navigate, similar to how sailors used the stars for centuries. During the day, birds watch where the sun rises and sets and use their internal clock to determine direction. At night, many birds navigate by recognizing constellations and star patterns. This method requires birds to have an accurate internal clock so they can account for how the sun and stars move throughout the day and year.
Visual landmarks and memory
As birds travel, they recognize and remember important geographical features like mountains, rivers, valleys, and coastlines. These landmarks help birds confirm they are on the correct path and adjust their route if needed. Birds with good memory can recall migration routes they've flown before or routes learned from other birds in their flock. This is especially important near the beginning and end of migration when birds need precise navigation to reach their destination.
Instinct and inherited knowledge
Young birds that migrate for the first time without experienced birds to guide them somehow still know the correct direction to fly and when to begin their journey. Scientists believe this navigation ability is partly inherited through genes passed down from parent birds. These instinctive behaviors give birds an internal map and compass that guide their migration, even without previous experience. However, birds also learn and improve their navigation skills over multiple migration journeys.
Multiple navigation methods combined
Birds don't rely on just one navigation method. Instead, they use several methods together to stay on course. For example, a bird might use magnetic field detection as its main compass, the sun position to confirm direction during the day, and landmarks to verify it's following the correct route. If one method becomes unreliable, such as when clouds block the sun, birds can switch to using their other senses. This multiple-method approach makes bird migration very reliable and successful. 
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