Tiny trackers on monarch butterflies to reveal secrets of 3,000-mile migration

A male monarch butterfly awaiting release following the placement of a transmitter (Carol Clark via AP)

Every August, monarch butterflies east of the Rocky Mountains in the US begin their migration from southern Canada and the northern United States to central Mexico to hibernate.

In the spring, when temperatures warm, they awaken, mate and begin their migration north again to lay their eggs.

In Texas, scientists with the National Wildlife Federation are now tracking monarchs during their migration to understand where they roost and protect the habitats they rely on.

As a child, Rebeca Quinonez-Pinon wondered where monarch butterflies stop for a meal and a night’s rest on their long migrations across North America.

Now she and other scientists are attaching tiny tracking devices to hundreds of butterflies to find those critical stopover locations before they disappear.

Swarms of dazzling orange-and-black monarchs use environmental cues to travel some 3,000 miles from as far as southern Canada to spend the winter in forests of oyamel fir trees in central Mexico, a protected biosphere reserve that is also a World Heritage site.

For decades, however, scientists have struggled to build a clear picture of the butterflies’ routes, how far they fly each day and where they settle at night.

Solar-powered radio tags attached to nearly 1,750 monarchs this year are helping provide answers.

As habitat loss, pesticides and climate change pummel monarch populations, the research could help their numbers rebound.

Ms Quinonez-Pinon said the uniquely famous monarch butterfly helps draw attention to the threats facing insects and their vital role in sustaining plant life across the continent.

“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.”

The public can follow the progress of individual butterflies on the free app called Project Monarch Science.

Only some monarchs migrate. Of the ones that do, a big portion of the butterflies east of the Rocky Mountains fly through a narrow corridor known as the “Texas funnel” every fall and spring, when they head north again to lay their eggs before dying.

But depending on the year, they might favour different parts of the Lone Star State, based on where they can find water, nectar and overnight shelters like trees.
Since the tracking started last year, scientists have found the first evidence of a butterfly in Utah, west of the Rockies, joining eastern monarchs in central Mexico.

Others migrated down the Eastern Seaboard to Florida, jumped the Gulf of Mexico and are now tracking across Mexico, a connection scientists had not seen before in such numbers.

The new 200 dollar (£150) tags weigh about as much as a drop of water and were developed by Cellular Tracking Technologies. If the person attaching the tag is properly trained and puts it on correctly, Ms Quinonez-Pinon said, “the monarch will be completely safe”.

Monarchs typically live two to six weeks, but the butterflies that migrate to Mexico can live up to nine months and spend their lives moving south, waiting out the winter and migrating north again before breeding in the spring.

The monarch’s feat has made it a symbol for the rights of international migrants.

Since the mid-1990s, the population of eastern monarchs has dropped more than 80%, and in the west by about 95%. Pesticides are a pervasive threat to milkweed, the plant where monarchs lay their eggs and the exclusive food source for its caterpillars.

Human-caused climate change, driven by burning coal, oil and gas, also a primary threat year-round, said Tierra Curry, senior scientist and endangered species codirector with the Centre for Biological Diversity.

“One of the problems now is that it stays too hot too long in the northern areas, and so they don’t get the cues to migrate.

“And then if the temperature freezes, they’re probably not going to make it to Mexico,” she said. “The later they start, the less the chances that they’re going to get all the way to the forest.”

Prolonged drought can dry up the water and nectar flower sources they need. They get hit by cars and trucks. And out in California, forests where western monarchs fly for the winter are being razed for development.

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.