Ottawa

Ontario's monarch butterfly comeback has roots in Texas

If you’ve wondered why there seems to be a resurgence of monarch butterflies in Ontario this year, it turns out the answer can be found about 2,800 kilometres to the southwest.

Population rose last winter after declining for 2 decades

Wildlife researcher Greg Mitchell says warm temperatures in Texas during the monarch's spring migration, combined with prime conditions for growing milkweed means that the monarch population can surge come summertime in Canada. (Greg Mitchell/CBC)

If you've wondered why there seems to be a resurgence of monarch butterflies in Ontario this year, it turns out the answer can be found south of the border — all the way in Texas.

In August, wildlife researcher Greg Mitchell co-published a study about the apparent boost in monarch populations and yearly fluctuations.

"What our study showed was that the year-to-year fluctuations are kind of driven by climate in Texas," explained Mitchell, who works for Environment and Climate Change Canada, on CBC Radio's Ottawa Morning. 

As it turns out, warm temperatures in Texas during the monarch's spring migration, combined with prime conditions for growing milkweed — a favourite plant of the butterfly — means that the monarch population can surge come summertime in Canada.

That's big news for the beleaguered butterfly, whose numbers have significantly dropped over the past two decades.

The monarch is currently classified as a "special concern" species under Ontario's Endangered Species Act, which means that while the butterfly is not considered endangered or threatened, it could be at risk of becoming so. 

Why Texas?

Monarch butterflies go through a multi-generational migration, which means that multiple generations of the species are born as the butterflies travel through a migration path.

The butterflies start off in the mountains of Mexico and make their way to southern Texas.

It's there that they find milkweed, the plant they feed from and on which they lay their eggs.

"If you see a patch of milkweed and there's a lot of chunks and whole leaves missing, that's a pretty good indication because [monarchs] eat a ton," Mitchell said. (Hallie Cotnam/CBC)

"Those eggs develop into caterpillars and then butterflies, then that generation migrates north again," Mitchell said.

It takes a couple more generations travelling north before the butterflies wind up in Canada.

"What we found was that if the temperature's really good in April or May down in the southern U.S., then we're going to see a lot of monarchs in Canada," he added. 

The other authors of the study are from the Insectarium de Montréal and Bird Studies Canada in southwestern Ontario.

Trend fluttering upwards

Mitchell said he's heard plenty of stories of people spotting the orange and black butterflies across Ontario this year, but that official counts have yet to be tallied.

"We won't know definitively until the Mexican government does their counts in the wintering grounds. That's how we know how big the population is," the wildlife researcher said.

"They all go to the same locations in the mountains in Mexico just west of Mexico City."

Wildlife researcher Greg Mitchell said he was in Mexico when the official counts were announced last winter. (Hallie Cotnam/CBC)

But last winter's count was overwhelmingly positive.

"We were up 144 per cent over the previous winter. The population size was six hectares so that's about six Olympic-sized track and field tracks," Mitchell said, adding that the estimate was just over two hectares the year before.

Notice all the butterflies flittering around Ottawa? Turns out the population of monarch butterflies has indeed jumped. But are they out of the woods? 6:21

Mitchell is cautiously optimistic that the upward trend will continue, but said that it all comes down to making sure there's enough milkweed to go around.

"We'll still have those big year-to-year swings, but we want the population to increase. And so the way that we do that is milkweed. The [butterflies] need milkweed to breed.  If there's no milkweed, there's no monarchs."

A monarch butterfly settles on some asters in Ottawa's Sandy Hill neighbourhood. The butterfly is classified as a special concern species in Ontario, but that could be changing. (Ian Black/CBC)

With files from CBC Radio's Ottawa Morning

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