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One of nature’s most beautiful events should get started over the next few weeks. Monarch butterflies will leave their winter homes in central Mexico and head north. They’ll fan out over the eastern two-thirds of the United States and into Canada. And they’ll use the brightest of all lights to guide them: the Sun.

Many animals navigate with the help of the Sun and stars, from birds to sea turtles. Monarchs do so using special cells in their brains. The cells process details about the Sun’s location in the sky. If the butterfly knows the time of day, then the cells can act as a solar compass.

A recent study found that the cells don’t switch on until the butterflies take to the air. Researchers studied the behavior of several monarch butterflies inside a flight simulator. They tied the butterflies to a rotating rod inside the simulator, and used tiny electrodes to monitor the monarchs’ brain activity.

They found that when the butterflies were on the ground, those regions of their brains were turned off. When they took to the air, though, the special cells turned on. The butterflies maintained their direction by keeping an eye on the simulated Sun in the sky.

The research team isn’t through with the study, though. The next step is to examine monarch behavior under more realistic sky conditions — in open-air simulators. The additional work will tell us even more about how these beautiful but delicate butterflies migrate across thousands of miles.

Script by Damond Benningfield

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