A sun and magnetic compass as guides
One of the main mysteries of that incredible journey is how Dani and her friends know where they are going. And how do they know when to leave?
Dani will know exactly when to leave, just like the rest of her congeners, she will use environmental cues such as the decrease in temperatures or day lengths that will trigger their internal clock that it’s almost time for their diapause.
How do they know where they are going:
That is a question that scientists have been working on for decades. How a small butterfly, that has never been to a specific place, will know its way to a specific forest thousands of kilometers away from where he/she were born.
There is still no clear answer to that question, but there are two main theories that could give an explanation to the monarchs sense of orientation:
A sun compass: Monarch butterflies are diurnal so they might use the sun's azimuthal position or the skylight polarization (when the sun is not visible) as well as a circadian clock mechanism in order to find their way.
A magnetic compass: Monarch butterflies could also use the magnetic field of the earth to indicate the inclination of the earth and guide their movement (just like sea turtles, or sharks) throughout their journey. So far, researchers believe that monarchs use a mix of their sun and magnetic compass to find their way.
Other theories, such as the use of landmarks, the detection of winds or simply genetics could also explain their sense of orientation.