Monarch Butterfly Migration Tracked
August 7, 2013

Scientists Track Monarch Migration, Find Worrying Signs Of Decline

Brett Smith for - Your Universe Online

Monarch butterflies are known for their annual migration that spans several generations and can extend from Canada to Mexico.

Tracking these majestic butterflies across thousands of miles and several generations has proven difficult for lepidopterologists, but new research published in the Proceedings of the Royal Society B has done just that and revealed new details about the majestic insect's life cycle in the process. Before the study, scientists only had a rough idea of how monarchs migrated across North America.

"You could have a monarch showing up in Ontario, but we didn't know exactly where it came from," said study co-author Ryan Norris, a biology professor at the University of Guelph in Ontario.

To track the butterflies, the team used chemical identifiers in the insects' wings to connect generational "waves" with their birthplaces. Because monarch larvae eat only milkweed, the plant's unique regional signatures shows up in the monarch's wings, allowing the research team to identify a butterfly's birthplace by chemical analysis.

Team members tracked monarchs' migration in the summer of 2011, capturing over 800 butterflies for analysis in the process. Starting in southern Texas, study researcher Tyler Flockhart said he logged almost 19,000 miles across 17 states and two provinces while tracking the insects.

"As far as I know, it's the broadest sample of monarch butterflies through an entire breeding season across North America," said the University of Guelph graduate student.

As expected, the monarchs were found overwintering in Mexico. As the breeding season commenced in April, the following generations of butterflies were born in Texas and Oklahoma. Later generations were born mostly in the Midwest and then subsequently over a broader area from the northeast coast stretching all the way back to the Midwest.

The researchers identified one important stop in the annual journey, the so-called "corn belt" in Midwest. From there, a breeding frenzy results in large numbers of adult monarchs spreading across North America in several directions.

Norris said the loss of milkweed plants and proliferation of genetically modified crops in recent years has severely impacted monarch survival rates.

"If habitats in the Midwest continue to decline, then monarchs will lose the ability to expand the breeding range, including those butterflies that end up here in Ontario," the Canadian researcher said.

Norris also emphasized the importance of protecting monarch habitats in other areas, such as parts of southern Texas, which spawn future generations headed for the Midwest.

"To lose monarchs would be a huge blow to the environment and to the public," Norris said. "People can easily identify monarchs. It might be the first butterfly they see or catch as a child, and it's often the first story they hear about how animals migrate."

Lepidopterologists have noted an unusually low number of monarchs in 2013. A report released last December said the butterflies overwintering grounds covered less than 3 acres, the smallest on record. A 1996 report from Yale researchers found an overwintering area roughly 18 times larger.

Experts have cited last year's drought and this year's unusually cold spring as reasons for the butterfly's less prolific numbers.