Monarch Migration to Canadian Prairies Larger than Normal Bruce Owen - Winnipeg Free Press
go to original July 5, 2012

Monarchs winter in the U.S. and Mexico and spend summer on the Canadian Prairies. (Ruth Bonneville/Winnipeg Free Press)

Manitoba and the rest of the Prairies are enjoying one of the largest migrations of monarch butterflies in recent memory.

A milder winter, an earlier spring, and perhaps some favourable winds, are bringing more of the orange and black insects from their wintering grounds in Mexico and the southern United States to Manitoba, Alberta and Saskatchewan.

"This is the progeny of the population that spent the winter in Mexico and is pretty large for us this year," University of Winnipeg biologist Richard Westwood said.

"They arrived quite a bit earlier than they normally do, primarily because we had such an early, early spring. That early, early spring really translated down to Texas and Oklahoma where a lot of our individuals also come from."

The monarch is known for its migration south and return to Canada in the summer, a trip that spans the life of three to four generations of the butterfly. Human threats to its wintering grounds have put the monarch at risk and in some jurisdictions there are efforts to classify it as a protected species and to restore its habitat.

For example, environmentalists are encouraging Prince Edward Island residents to plant milkweed in their gardens to boost the monarch butterfly population on the island. Milkweed is the monarch's host-plant where females lay their eggs.

Cheryl Tyndall, curator of the Niagara Parks Butterfly Conservatory, said in an email that a milder winter in North America helped boost the number of monarchs in their wintering grounds.

"A short, mild winter often results in an increase in the survival of winter populations," Tyndall said. "All in all, the ideal weather and abundant food had monarchs across Canada turning up earlier, and all at the same time, resulting in what appears to be a higher population than normal."

In normal migration years, the monarch arrives in Manitoba mid-June to early July. But this year, Manitobans started spotting them in late May, about three to four weeks earlier than last year, Westwood added.

Those returning butterflies also remained healthier longer because of our warm weather, and because they've found abundant milkweed.

"There are still a few individuals flying around out there, but they're pretty worn and they're mostly females still laying eggs," Westwood said. "Most of the males probably aren't with us anymore. They're usually shorter-lived."

While that means the number of monarch sightings in southern Manitoba has dropped, that won't last long. With the high numbers that migrated, it means more eggs were laid and more monarch caterpillars will develop, creating an explosion of monarchs starting in late July.

"I grow a whole patch of wild milkweed and it's covered in caterpillars right now," Westwood said. "We'll probably start to see the new group of monarchs that will fly south in about two to three weeks."

Manitobans can help the monarch by devoting a part of their yard to milkweed.

"It's all about providing habitat for them," he said. "Luckily, in Manitoba we have enough wild areas that there is enough milkweed around. It's why the monarch generally does quite well here."

How long the Manitoba-born monarch hangs around before fluttering south depends on what brought its parents to the province so early: favourable weather and plentiful food sources, both of which are in good supply this summer.

bruce.owen@freepress.mb.ca

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