The number of monarch butterflies migrating from Canada and the US to Mexico has increased this year, a hopeful sign following a worrying 75 percent drop in their numbers last year, experts reported this week.
The total amount of forest covered by the colonies – millions of orange-and-black butterflies that hang in clumps from the boughs of fir trees – more than doubled from last year’s historic low.
But concerns persist about the monarchs’ long-term survival, because their numbers remain well below average.
This winter, there are four hectares of colonies, more than double the 1.9ha last year, the lowest level since comparable record-keeping began in 1993.
“These figures are encouraging, compared to last year, because they show a trend towards recovery,” said Omar Vidal, director of the conservation group World Wildlife Fund Mexico, which sponsored the study along with the government Commission on Natural Protected Areas and the cellphone carrier Telcel.
Despite the rebound experienced by this mysterious scientific phenomenon, historically a huge tourist draw, the latest numbers are well below the almost 8ha covered in the 2008-09 winter season and the record high of 18.2ha in 1996-97.
“Fluctuations in insect populations are normal in nature,” the study’s sponsors said in a statement. “With regard to the monarch butterfly, these fluctuations could be due mainly to climatic conditions,” including especially cold or dry years in the US and Canada, where the butterflies that make the trip are born. But experts said natural variation doesn’t fully account for a long-term decline in average numbers.
Lincoln Brower, an expert on monarch butterflies and zoology professor at the University of Florida, said this year’s recovery is good news, but adds that each time the butterflies “recover,” they slip to lower and lower numbers.
“What is ominous is that all of the last seven years have been below average,” he said.
Brower points to several possibilities for the decline: climate changes, deforestation, and the existence of genetically modified crops and pesticides, which crowd out the milkweed plants where monarchs lay their eggs.
No monarch lives long enough to make a round trip from the US and Canada to Mexico. Some colonies return to patches of forest that have been dangerously denuded by logging or severe storms. The preference for areas they “know” can create a death trap.
Brower is investigating the hypothesis that if butterflies somehow “mark” their wintering grounds, perhaps chemically, that marker could be replicated and lead the monarchs to areas where they would be safe. – Sapa-AP