Monarch butterfly resurgence might not take flight, says Ottawa prof

Monarch butterflies have made a big comeback in their winter home near Mexico City, but an Ottawa professor says this year's rebound may have as much to do with good luck as good planning.  

University of Ottawa biology professor Jeremy Kerr recently visited a forest west of the Mexican capital, where he saw the winter habitat of the butterflies for the first time.

On Friday, he joined CBC Radio's All In A Day to talk about the trip, the resurgence, and what it all means.

"A lot more of them made it back by virtue of good weather, and now the trick for us is to make sure our activities there are going to support large populations — now and in the future," Kerr said.

"There is a risk that this is a blip, and that's the reason we have to be careful not to simply rest on our laurels."

Each day, volunteers and researchers head out into the oyamel fir forest to count the butterflies — a safe haven for the winged insects.

They calculate the population by measuring how much of the forest is occupied by the butterflies, which can number in the millions.

"Monarch populations in the overwintering sites this year have increased by about 140 per cent relative to last year," said Kerr, bringing the winter population back to the level it was 10 years ago.

'Literally millions of them'

In fact, Kerr said the sheer density of butterflies in forest was "one of the most magical" experiences he'd ever had as a professional biologist.

"Suddenly you find yourself in clearings where the butterflies are roosting in these trees, and there are literally millions of them. And the sunlight areas above you are filled with clouds of monarch butterflies moving through the air. It's unlike anything I've ever seen as a butterfly biologist," Kerr said.

"Thousands of butterflies around you take flight all at once. If you close your eyes and just really concentrate on your hearing, you can actually hear what sounds like a whispering wind in the trees."

Kerr encouraged people in Ottawa to plant a variety of milkweed in their gardens to provide habitats for the butterflies when they return this summer.