How do monarch butterflies navigate 3,000 miles to a place they have never been?

The answer

Monarch butterflies migrate up to 3,000 miles from eastern North America to specific oyamel fir forests in central Mexico using a time-compensated sun compass located in their antennae that integrates the sun's position with their internal circadian clock. They also appear to use Earth's magnetic field as a backup navigation system on overcast days. The migration takes multiple generations heading north in spring, but a single super-generation flies the entire southward journey in autumn, arriving at groves they have never visited. Scientists believe the navigation program is encoded genetically, passed down through generations without any learned component.