By analyzing the ‘chemical fingerprints’ in the wings of monarch butterflies, one Western researcher has helped pinpoint the North American birthplaces of the migratory creatures, vital information that may help conserve the dwindling species.
“What we are seeing is not only is the populations going down in the Midwest (United States), but they are getting hit everywhere, through weather changes, pesticides, deforestation,” said Biology professor Keith Hobson, who worked on the project with lead investigators at the University of Guelph. “There is not one area we can point to and say, ‘That’s the problem.’ There is a huge concern.”
Each fall, as many as 60 million, and up to one billion, monarch butterflies journey from eastern Canada to the forests of western central Mexico, a trip that spans more than 4,000 kilometres. They spend their winter in hibernation, clustered in the Monarch Butterfly Biosphere Reserve, a World Heritage Site and national protected area and nature preserve covering more than 200-square-miles, before making the long return trek back north in the spring.
Hobson, who has been to the site in Michoacán, Mexico numerous times, most recently this past year, said there were 14 roost sites at the reserve in the mid-1990s. Today, there are four.
“You can’t possibly imagine seeing the butterflies quivering on the trees. You could sit there for hours just watching them,” he said. “As an insect, to undergo a 4,000-kilometre migration is one of the wonders of the world. How do they find these roost sites in Mexico? These same trees are used every year.”
For the past two decades, however, the monarch population has dropped significantly. Researchers attributed that fact, somewhat, to the eradication of milkweed, a plant vital to butterfly breeding, across North America.
“While the species will probably not become extinct – there are non-migratory species around – the phenomena of millions of butterflies going down to Mexico and coming back year after year, that is in great danger of being lost,” Hobson said.
Once within the confines of the Mexican reserve, the monarch butterflies spend the next five months clustering together and covering the tree trunks and branches in a blanket of orange and black. In many instances, the weight of the butterfly clusters is enough to cause tree branches to bend or snap.
Fertile females leave around the end of March, heading north toward Texas, making frequent stops to lay their eggs on milkweed plants, where, six weeks later, new generations are born and continue the trek north to the next stop, where more eggs are laid. By the time they reach southern Ontario – to popular areas such as Long Point and Point Pelee, by late May or early June – the butterflies are several generations removed from the ones who originally left Mexico.
A technique to track migratory insects establishes a ‘fingerprint’ of the butterflies by looking at the distribution of certain isotopes and elements in chemical compounds within each insect.
Analyzing more than 1,000 samples, going as far back at the mid-1970s, Hobson looked at the signatures to determine where the butterflies were born in the previous summer and fall. This is the first detailed study to look at where overwintering monarch butterflies are born, over multiple years, he added.
The largest percentage of monarchs migrate to Mexico from the American Midwest, but the insects’ origins were spread evenly throughout Canada and the United States. The study, published earlier this month in Global Change Biology, found 12 per cent of the insects were born in the northwestern United States and Canadian Prairies; 17 per cent in the north-central United States and Ontario; 15 per cent in the northeastern United States and Canadian Maritimes; 11 per cent in the south-central United States and 8 per cent in the southeastern United States.
“We expected the majority to be found in the Midwestern states,” said Tyler Flockhart, lead author and Liber Ero Postdoctoral Fellow at the University of Guelph. “However, just 38 per cent come from that part of the United States. If we just focus conservation activities on this area, we will be missing a number of butterflies born elsewhere in North America.”
Along with Western, Guelph also collaborated with the University of Georgia, Sweet Briar College in Virginia, Universidad Nacional Autonoma de Mexico, Environment Canada and the International Atomic Energy Agency.
In North America, milkweed, a vital plant used by the butterflies to lay their eggs, has been treated as a pest by the agriculture community. Perhaps producing controlled areas that are not agriculture based is possible, Hobson said.
“It is feasible we could lose the migration with time, if it keeps going like this, within the next 10 years. It’s not a lost cause by any means, but we can expect this (decline) to continue,” Hobson said. “They can live year-round in areas such as Texas, Louisiana and the southern United States, but we (Ontario) could have a chance of losing them. If there is a tangible environmental topic that can be addressed, this is it.”