How do turtles know where their home beaches are to return to to lay their eggs?

Question: How do turtles know where their home beaches are to return to to lay their eggs?
- Keywords:
  egg,
  navigation,
  turtle
Asked by fiona to Rupert on 17 Mar 2017.
- Rupert Marshall answered on 17 Mar 2017:
  
  Loggerhead turtles have a magnetic sense of home. They follow the earth’s magnetic field back to the beach to lay their eggs. The thing is that the earth’s magnetic field varies slightly over the years. The turtles still follow the magnetic field, changing their destination slightly as a result, as if someone has twisted the signposts a bit.

Question: How do turtles know where their home beaches are to return to to lay their eggs?