Circadian Clocks

• Birds are able to determine their location and destination when migrating based on the location of the sun and their natural sense of time. An animal's internal sense of time is known as its circadian clock or circadian rhythm, defined by scientists as a daily rhythmic activity cycle based on 24-hour intervals.
  
  

Determining Direction

• Using their circadian rhythms, birds determine migratory direction based on their relation to the sun. They can observe the arc of the sun and extrapolate it to its highest point then compare it to the position of the sun at their departure point. From this information, birds can determine a general idea of which direction their departure point was (north or south and east or west) and what direction they need to travel to continue their migration.
  
  

Polar Birds vs. Tropical Birds

• Interestingly enough, experiments have shown that birds native to climates in very low latitudes near the equator have extreme difficulty finding their way in solar conditions that replicate very high latitudes, such as polar climates. The same is true for native polar birds. They have difficulty finding their way in tropical solar conditions.
  
  

Other Migratory Clues

• Birds' solar compasses are not the only tool they have for finding their way. Birds also have a hardwired sense of magnetic north. They also use visual clues, sounds and smells from the landscapes to help them determine their destination.