Flight paths: Tiny trackers aim to unravel monarchs’ migration mystery

DORANY PINEDA

As a child, Rebeca Quiñonez-Piñón wondered where monarch butterflies stop for a meal and a night’s rest during their long migrations across North America. Now, she and other scientists are attaching tiny tracking devices to hundreds of butterflies to identify these critical stopover locations before they disappear.

Swarms of orange-and-black monarchs travel 4,800 kilometres from southern Canada to spend the winter in forests of oyamel fir trees in central Mexico, part of a protected biosphere reserve and a World Heritage site.

For decades, scientists have struggled to map the butterflies’ routes, daily flight distances and overnight stops. Solar-powered radio tags attached to nearly 1,750 monarchs this year are helping provide answers.

As habitat loss, pesticides and climate change threaten monarch populations, the research could help their numbers rebound. Quiñonez-Piñón said the butterfly’s fame draws attention to threats facing insects and their role in sustaining plant life.

“Pollinators are crucial to protect and ensure that our ecosystems remain healthy,” she said, “and also to have the sources of food that we require as humans.”

Only some monarchs migrate. Many east of the Rocky Mountains travel through a narrow corridor known as the “Texas funnel” every autumn and spring. In spring, they head north to lay their eggs before dying.
Depending on the year, they may favour different parts of Texas, depending on where they find water, nectar and overnight shelter.
Since tracking began last year, scientists have found the first evidence of a butterfly from Utah, west of the Rockies, joining eastern monarchs in central Mexico. Others travelled down the Eastern Seaboard to Florida, crossed the Gulf of Mexico and are now being tracked across Mexico — a connection not previously seen in such numbers.

“There’s just all these unique stories of their paths, connections between the population, that we didn’t know existed or we hypothesised but couldn’t prove,” said Emma Pelton, senior conservation biologist with the Xerces Society for Invertebrate Conservation.

Since this year’s migration began, about 175 tagged butterflies have been detected in Mexico. The $200 tags, developed by Cellular Tracking Technologies, are extremely light. If fitted correctly by a trained person, Quiñonez-Piñón said, “the monarch will be completely safe”.

Not every monarch is suitable for tagging. Most tagged butterflies weigh more than 400 milligrams, about as much as a standard pill, to avoid overburdening them, said David La Puma, vice-president of global market development at Cellular Tracking Technologies and coordinator of the Project Monarch Collaboration, which the National Wildlife Federation recently joined.

Monarchs are caught in nets and kept cool before tagging. Each is positioned on a special board, its legs and antennae protected. Adhesive is applied to its abdomen and the tag gently pressed against its body before it is released.

Last year, the Trump administration delayed a decision on federal protections for monarchs. Several groups filed a lawsuit, and a court ordered the government to make a final decision by 2030. Conservationists are pressing ahead with new ways to protect the dwindling population.