The number of monarch butterflies wintering in Mexico is at its largest in at least 10 years, raising hope for the colourful but endangered insect.
Monarchs spread out across southern Canada and the United States in summer, but their descendants all return to a tiny patch of high-altitude fir forest in Mexico in the winter. This is where researchers take a census — not counting the monarchs, but measuring the area of forest they cover as they huddle together.
This winter, the area is about six hectares, more than double the size of last year’s population.
The University of Ottawa’s Jeremy Kerr, an insect scientist who specializes in butterflies and moths, is in Mexico now. He says it is “wonderful news.”
“Here is the deal, judging from the data. The massive amounts of work that the three nations (Canada, United States, Mexico) have been doing is probably helping. We are setting the stage for population growth of this iconic species,” he said in an email.
“These colonies have reached a size of six hectares of densely packed butterflies.” It is the largest group in 10 years “and it’s a big difference from last year.
“There is a catch. It is a single point on a long and highly variable trend for monarchs. It could be a great moment where we see stable recovery. It could also be a temporary uptick that falls back down next year.”
The good news from Mexico follows a summer when monarchs were common around Eastern Ontario.
“The weather was just great for monarchs in the spring (and) through the autumn return journey to Mexico,” Kerr said. “A lot more monarchs made it back than has been normal over the past decade. But the weather is a fickle friend, especially these days when extreme events are clearly becoming more important.
“So, we have wonderful news. Many people — from community members around here in Mexico to citizen scientists in Canada and dedicated researchers everywhere — have worked hard for a glimmer of good news. We got the glimmer. Now it is time to work on the longer term trend.
“What I hope we might see is a second year of good overwintering populations. That would make me feel like this good news might be durable.”
A major threat to monarch is habitat loss. The insects depend on milkweed through the full length of their migration, and milkweed has been widely eradicated from both farmland and cities.
Jeremy Kerr is affiliate professor at the Institute of the Environment, and full professor at the Department of Biology at the Faculty of Science at the University of Ottawa.