Scientists said the number of monarch butterflies which will start their annual migration north to Canadian gardens and wild flower patches this summer is down sharply thanks to extreme weather last fall. (Photo by THE CANADIAN PRESS)

Extreme weather, forest loss behind sharp drop in monarch butterfly spottings

OTTAWA — Right about now, the kings of the butterfly world are emerging from hibernation in Mexico looking for love and ready to make more butterflies.

But scientists Monday said the number of monarch butterflies which will start their annual, 5,000-kilometre migration north to Canadian gardens and wild flower patches this summer is down sharply thanks to extreme weather last fall.

A survey released Monday by the World Wildlife Fund and the Mexican National Commission for Protected Areas showed a 15 per cent drop in the forest area occupied by hibernating monarchs in the fir forests of central Mexico this winter.

In absolute terms, that’s likely a loss of about 16 million butterflies compared with this time last year. Monarchs are a critical element in the North American ecosystem, pollinating a number of wild flowers and serving as food for birds and other insects.

Emily Giles, senior specialist for species conversation with the World Wildlife Fund Canada, said the population of monarchs goes up and down but over the last 25 years the overall trend has been downward.

“We think this again is just another indicator of another species, and another pollinator species, that is in decline,” said Giles.

Monarch butterflies have already been assessed as endangered in Canada, she said.

This last year, a warmer than usual fall lulled the butterflies into delaying their annual southern flight to Mexico, and when they did start to make the trip, many were killed in hurricanes and tropical storms that pummelled North America.

“This year, researchers in the states have identified that we had a number of weather events that likely impacted the migrating population,” said Giles.

The population is measured by the size of the forest area where scientists can locate them during hibernating months in December and January. In 1993, the butterflies were found in about 6.23 hectares of forest in central Mexico in the states of Mexico and Michoacan — about the equivalent of 12 football fields.

Last year, the size of the forest where scientists could trace the butterflies was 2.48 hectares, or only about 4.5 football fields.

Habitat loss due to deforestation coupled with extreme weather events linked to climate change are largely to blame, says the WWF report.

Monarchs go through at least four generations each year — three of which last from six to 10 weeks and take place in the United States and Canada between March and September. The fourth generation lives for months, migrating south to Mexico and southern California where they hibernate over the winter before emerging to fly back north and lay new eggs in the spring.

Research at Cornell University suggests the declining population is largely the result of die-off during the migration period because of weather and issues with the hibernation grounds themselves.

Giles said Canadians can help the species revive by planting milkweed in their gardens, a species of native plants that is the only type of plant where monarchs will lay their eggs.

She said a lot of milkweed has been eradicated over the last few decades by herbicide applications. so replacing those plants is a critical element to keeping the monarchs from disappearing.

“It’s a species we can all help and I think we all love and care about this species,” she said. “It’s kind of a national icon in a lot of ways.”

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