Professor Brian Cox explains how Monarch Butterflies navigate by “monitoring the position of the sun, and compensating for its location in the sky using their internal timekeeping mechanism… even when it’s cloudy.” This is an episode 5 preview of the BBC’s Wonders of Life. Full screen this.

Updated reading: Monarch Butterflies Use a Magnetic Compass During Migration:

Monarchs use a time-compensated sun compass in their antennae to help them make their 2,000-mile migratory journey to overwintering sites. During the absence of daylight cues, such as under dense cloud cover, migrants have been, surprisingly, seen flying in the expected southerly direction. It’s been hypothesized that monarchs use geomagnetic cues to help navigate when day light cues are unavailable to them during migration…

Using flight simulators equipped with artificial magnetic fields, Patrick Guerra, a postdoctoral fellow in the Reppert lab, examined monarch flight behavior under diffuse white light conditions. He found that tethered monarchs in the simulators oriented themselves towards the south. Further tests in the simulator revealed that the butterflies used the inclination angle of Earth’s magnetic field to guide their movement. Reversing the direction of the inclination caused the monarchs to orient in the opposite direction, to the north instead of the south.

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