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In an average year, 350 million monarch butterflies are seen wintering in Mexico. This winter, there were only about 60 million – a difference of more than 80 per cent, according to an official count by the World Wildlife Fund and the Mexican government. (FLIGHT OF THE BUTTERFLIES 3-D)
In an average year, 350 million monarch butterflies are seen wintering in Mexico. This winter, there were only about 60 million – a difference of more than 80 per cent, according to an official count by the World Wildlife Fund and the Mexican government. (FLIGHT OF THE BUTTERFLIES 3-D)

Why monarch butterflies’ numbers are in freefall Add to ...

In an average year, 350 million monarch butterflies are seen wintering in Mexico. This winter, there were only about 60 million – a difference of more than 80 per cent, according to an official count by the World Wildlife Fund and the Mexican government.

Those numbers – the lowest in 20 years of recorded history – have experts wondering if, and how, monarchs can bounce back from this significant decline in their population.

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For Canadians, the reality hit home in July when butterfly lovers and naturalist clubs began recording their first monarch sightings of the year, about six weeks later than usual. Monarchs leave their breeding grounds in Ontario and the United States each fall, heading south to Mexico through the midwestern United States. They leave Mexico again in early March, returning to their northern breeding grounds.

The first monarch butterfly sightings are usually recorded in the southernmost tip of Ontario in early June. This year, the first sightings occurred in mid-July – a time when the butterflies should already be nestled in their breeding grounds. The number of butterflies being recorded is also dismally low: In regions where more than 100 monarchs were spotted in the province last year, fewer than five have been observed this year.

Monarch populations have been gradually declining over the last eight years, according to Donald Davis, chair of the Monarch Butterfly Fund, who has been tagging monarchs since 1967. The organization, dedicated to the conservation of monarch butterflies, is comprised of academics, butterfly lovers and environmentalists.

“I have never seen them this low,” Mr. Davis says. “Ever. In all my years of studying monarchs.”

Experts don’t know for sure why the monarch is so late to appear this summer or why their numbers are dwindling. One reason could be a loss of habitat, Mr. Davis says. Monarchs rely exclusively on the milkweed plant to reproduce, but over the years milkweed has been treated aggressively with pesticides for being a noxious weed.

Another potential factor could be the drought in the spring and summer of 2012 in the central United States, Mr. Davis says. “The butterflies don’t do well or reproduce in drought.”

Last year, monarchs showed up early in Ontario, after migrating through drought conditions. They arrived before milkweed was even out of the ground.

The combination of drought and loss of milkweed not only would have affected the monarchs’ ability to reproduce, but also to store fat reserves in their abdomens for the journey back to Mexico, Mr. Davis says. Dry conditions in some parts of Ontario last fall would not have helped the monarchs either, he adds.

This year, the migration back to Ontario wasn’t any easier for the monarchs – already low in numbers – with a chilly spring all across the south. The cold-blooded insects are extremely sensitive to temperature, says Elizabeth Howard, founder of Journey North, the organization that tracks the monarchs’ migration through reports of first sightings across the continent.

“They can’t even fly until their flight muscles are 55 degrees Fahrenheit [13 C]. So, they can’t even migrate. They are basically stuck in their tracks by the cold,” she says.

Since a monarch’s life span is only about two to four weeks – one migration can comprise several generations of the butterflies – an entire generation is missing in Ontario.

“What that means is that each generation is not producing very many monarchs,” Ms. Howard says. “The significant thing beyond that is that fall migration starts in August. So, we’re looking at the breeding season ending before the numbers really build.”

Ms. Howard says the monarchs need warmer temperatures to make up their numbers. “This year is an extreme. Nobody knows if they can recover from these levels. They may bounce back, but it doesn’t look very good.”

The extremes in weather conditions, she adds, stem from climate change. “I don’t think this is a stretch to say how this is an example of how climate change is affecting a species.”

Mr. Davis expresses similar concerns and suggests that a solution may be for people to create “monarch butterfly way stations” with plenty of milkweed to help the butterflies stay healthy along their journey.

He is also encouraging people to report monarch butterfly sightings on ebutterfly.ca as the sharing of information can be helpful.

 

MONARCHS BY THE NUMBERS

  • 17: Acres of trees that monarch butterflies cover, on average, while wintering in Mexico. In an average year, 350 million monarchs winter there
  • 3: Acres covered during 2012-2013, when about 60 million monarchs wintered in Mexico
  • 52: Highest recorded forest area covered by monarchs in Mexico, in 1996
  • 185: Monarchs found last July at the annual Presqu’ile Provincial Park Butterfly Count
  • 3: Number this year
  • 768: Monarchs found last year at the Haliburton Highlands Butterfly Count
  • 31: Number this year

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