A monarch butterfly flies through trees in El Rosario Reserve, part of the Monarch Butterfly Biosphere Reserve in the central Mexican state of Michoacan. Butterflies that traveled over the winter in the same Oyamel fir forest as their ancestors. (Photo by Jaime Rojo)
This article is a feature article published in the January 2024 issue of National Geographic magazine. Only regular subscribers can read the entire article.
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This article was sponsored by the National Geographic Society, a nonprofit organization dedicated to preserving Earth's resources.
Monarch butterflies undergo an epic transcontinental migration from southern Canada to Mexico. Butterfly lovers are doing their best to protect the butterfly as its population declines due to climate change and habitat loss.
On a sunny day in October, a man was hunched over a makeshift workbench in the mountains of Texas, USA.
I deftly held the beautiful wings of a monarch butterfly between my thumb and forefinger, then ran a strip of sandpaper down its body to shave off the tiny hairs.
The man, Andre Green II, and his fellow researchers rented a hunting lodge and used it as a research base. The walls of the hut are lined with carvings of hunting animals, but Green doesn't notice them. The University of Michigan professor of ecology and evolutionary biology and National Geographic explorer focuses on the more than 30 monarch butterflies he caught that day.
Green placed a drop of epoxy resin between the wings and fitted the butterfly with a special sensor. The device consists of a small solar panel and a computer chip, but it weighs less than three grains of rice. The soft sound of a butterfly's wings echoes around the room.
The monarch butterfly will now travel 800 miles south with its friends to the mountains of central Mexico. In anticipation, Green and his team will head to Mexico in a few weeks, looking for signals from sensors there. Sensors record light and temperature information along the migration route. Receiving data from just one or two animals can help determine migration routes.
In North America, monarch butterfly enthusiasts volunteer to help search for this butterfly. The same is true of the study by Green et al. Monarch butterflies fly at the speed of a bicycle, so Green's colleagues tested the accuracy by having cyclists wear the sensors and ride the bikes for several days. Green himself confirmed through laboratory experiments that the sensor did not interfere with the butterfly's flight. After repeated preparations, the final sensor is finally ready for production.
A female sucking nectar near Ames, Iowa. He is wearing a tracking transmitter. (Photo by Jaime Rojo)
After installing the sensor, Green sinks into a large leather chair and watches the monarch butterfly in its cage. “If I can get a signal in Mexico, I'd say it's good for this year.” Getting the data right will likely be a long process of trial and error over several years, but Green is patient. “It's a once-in-a-lifetime opportunity to understand the mechanism of migration,” he said, expressing his enthusiasm in an understated way to describe the world.
When it began to get colder outside, Green carried the cage out of the cabin and down into the grove of trees by the creek. It was a forest of pecan trees, which belong to the walnut family, and hundreds of monarch butterflies were flying around in the slanting sunlight. Green takes the sensor-equipped monarch butterflies from their cages and gently places them one by one on a low branch, as if he were handling a piece of glass.
If all goes well, it will resume its journey south with the sensor the next morning.
Andre Green II attaches a sensor to a monarch butterfly that weighs less than three grains of rice. (Video: Thor Morales)
Next page: One of the most epic and dangerous journeys on Earth
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