Poor weather among reasons insect population down 75 per cent
By Mark Hume
As she worked in her garden last summer Theresa Fowler noticed that something vital was missing.The species assessment specialist with the Canadian Wildlife Service didn’t find a single monarch butterfly caterpillar.
Canada’s national insect, a big, brightly coloured butterfly that each year brings the countryside alive from British Columbia’s Okanagan Valley to the East Coast, had all but vanished.
Usually the milkweed plants Ms. Fowler nourishes on her property, because they are the only plant on which monarch larvae can live, are crawling with the distinctly marked caterpillars.
“There weren’t any last year,” she said. “None.”
A report yesterday pointed to an alarming collapse in the monarch butterfly population.
Mexico’s Environment Department said that 75 per cent fewer monarch butterflies have appeared in 2005 compared to previous years, blaming cold weather and agricultural practices in Canada and the United States.
The dramatic orange and black butterflies that Ms. Fowler usually sees on her property in Shawville, Que., north of Ottawa, and which are found across much of southern Canada, migrate nearly 5,000 kilometres each fall to Mexico.
A second, smaller wintering area exists in California.
But most monarchs, up to 200 million, head for Mexico where they cluster for the winter in a few forested areas.
In the spring, they head north again and disperse across North America.
Ms. Fowler, a butterfly expert who chairs a subcommittee of the Committee of the Status of Endangered Wildlife in Canada, said many experts believe the insects’ real problem probably lies in Mexico, where illegal logging has been an issue for years.
She said it’s too soon to say if a trend has begun or if there has just been a temporary collapse. What is clear is that the monarchs are missing in Canada.
“The population varies a lot and sometimes there are fairly large fluctuations,” Ms. Fowler said.
“But this last year the number appears to have been very, very low. One of the very lowest.”
She said reports she got from around the country indicate her garden wasn’t the only place devoid of monarchs.
“It was just anecdotal, but a lot of people told me they just weren’t seeing them like they used to,” she said.
Estimating the population in Canada is difficult because the butterflies, easily recognizable with their lilting flight and orange wings tipped with black, don’t gather in one place.
In Mexico, however, they concentrate in oyamel fir forests, many of which are now in protected preserves, clustering so heavily that tree branches droop from their collective weight.
The winter gathering gives researchers a chance to get an idea of the population numbers, although estimates are difficult because studies have found densities range from seven million to 61 million monarchs per hectare.
The Mexican report did not give a population number but estimated a 75-per-cent decline based on reports from 12 of 22 nesting grounds.
A 75-per-cent drop isn’t unheard of. That many died in Mexico during freak snowstorms in 1992 and in 2002.
But to have such a high percentage simply fail to arrive indicates something has gone wrong that is more serious than an isolated weather event.
Robert Pyle, a researcher who has studied the butterflies for more 30 years and who is the author of Chasing Monarchs, said the dramatic decline is disturbing.
“We’ve had population failure several times in the past decade, this being the worst, …[but] to have two dramatic low numbers so close together I think is very definitely a concern,” he said.
Mr. Pyle said illegal logging in Mexico is most likely the cause.
“I think, from the evidence I’ve encountered, that the greatest part of the diminution of the monarch numbers both this year and in the past can be laid at the feet of the continued deterioration of the forest,” he said.
Lincoln Brower, a professor at Sweet Briar College in Virginia and one of the world’s leading authorities on monarch butterflies, rejected the Mexican suggestion that the cause of decline lies in Canada and the United States.
“That’s ridiculous. The fact of the matter is… the Achilles’ heel is down there in Mexico because that is where the monarch butterflies concentrate.”
Mr. Brower has warned for years that logging in the monarch butterfly sanctuaries could put the population at peril.
“This is the lowest we’ve seen it in 14 years of monitoring. There is reason for concern,” he said.
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