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A monarch butterfly rests on a flower. (File Photo).Charlie Neibergall/The Associated Press

One of nature’s greatest migrations may be returning to health after a stunning growth in the number of monarch butterflies that fluttered across North America last year.

Every year, the main population of monarchs numbering in the tens of millions migrates from Canada and the United States to overwinter in Mexico. That’s a journey of more than 5,000 kilometres undertaken by tiny creatures weighing less than a gram.

In recent years, the number of monarchs making the flight plummeted by about 90 per cent from historic numbers, says Carolyn Callaghan of the Canadian Wildlife Federation.

Scientists estimate monarch numbers by measuring a tiny patch of central Mexican forest where they congregate. There can be anywhere from 10 million to 50 million monarchs per hectare.

As recently as 1993, the butterflies took up 6.2 hectares. Last year, the size of forest where scientists could find them was down to 2.5 hectares.

Something, though, seems to have gone very right since then.

A newly released survey for 2018 found monarchs on more than six hectares of forest, which would suggest population numbers were up 144 per cent over 2017. One year’s increase is not necessarily a trend, but it’s good news.

“It’s a reprieve from a dire situation,” said Callaghan.

In addition to good weather – the previous year’s butterflies had been pummelled by tropical storms and tornadoes – a three-country agreement to bring back the monarch may finally be paying off, she said.

Mexico has cracked down on illegal logging that destroyed monarch habitat and is working to create ecotourism opportunities as a replacement. The U.S. has engaged in extensive replantings of the weeds and wild flowers monarchs need for nectar and egg-laying.

“I’m astounded at what they’ve been able to do,” said Callaghan. “The state of Ohio alone has restored more than (32,000 hectares) of habitat.”

Much of that has consisted simply of planting milkweed and wild flowers along highway meridians, power corridors or other unused plots of land.

Southern Canada, especially Ontario and Quebec, contains important monarch breeding grounds. About one-third of the butterflies that show up in Mexico have been found to have originated in Canada or the northern states.

The butterflies are considered endangered but are not yet protected under the Species at Risk Act.

The Americans and the Mexicans have far surpassed Canadian efforts to restore habitat, Callaghan said. That’s despite an agreement signed in 2016 between the leaders of the three countries to address habitat loss across breeding and migrating habitat.

“We have a role to play,” Callaghan said. “We have yet to do this. Canada, well, hmm. Not so much going on.”

Canadian wildlife officials dispute that. They say the species is considered a priority and $14-million has been spent since 2012 on the butterflies.

Andrea Kettle of the Canadian Wildlife Service says that although Canada doesn’t directly run monarch habitat programs, it has worked with and funded about 50 outside organizations that have. Research is also being done to determine which areas are most important, Kettle said.

“It wasn’t that long ago that milkweed was on a noxious species list, so it had a bad reputation. The behavioural change to encourage people to plant milkweed has been undertaken by lots of organizations that we have supported.”

Canada could be doing more, said Callaghan.

“The U.S. has had a huge lead on us. Every (state) department of transportation is taking on restoration, mowing less, planting native flowers.

“We can do that on our hydro lines. We can do that on our roadways. We can do that on our buffer lands. We haven’t even begun to hit the tip of the iceberg here in Canada.”