Low monarch butterfly populations in Mexico disappointing to N.B. naturalist

Naturalist Jim Wilson is amazed by how something as simple as holding a monarch butterfly can bring out emotions in people.

The Quispamsis man has been tagging New Brunswick monarchs for more than a decade to help researchers track their migration, and he often invites people to help out.

"It's astounding to me how it grabs them," Wilson said about the experience. "And I'm talking about big, rugged guys who should be working on a pipeline or wrestling bears."

It's probably a good thing the little orange and black butterfly elicits such a loving response, because these days the monarch is in trouble.

And its peculiar migration habit is part of the reason why we know they're struggling.

Across North America, every monarch butterfly that transforms from larval stage in late summer heads to the same place: a section of forest in the mountains of Mexico. 

There, they gather in huge colonies to wait out the winter.

By measuring the size of those colonies, biologists can get a good idea of how the species is doing.

And over the past two decades, the colonies have shrunk dramatically.

That has led to continent-wide efforts to protect the monarch's habitat, and the only plant it will lay its eggs upon: milkweed. Here, Nature NB, a non-profit conservation group, has been encouraging gardeners to plant the non-invasive swamp milkweed in their flower gardens.

Those efforts appeared to be working. After reaching a crisis point in 2013, when the Mexico colonies measured a mere 0.67 hectares in size, a fraction of the average 5.5 hectares normally seen in the past two decades, the population slowly regained strength.

And in the winter of 2018-2019, it soared up over six hectares, giving monarch fans like Wilson reason for hope.

Wilson said the tagging season last year reinforced that optimism.

Setting up at the Saint John Naturalist Club's site at Point Lepreau from mid-August to mid-September, Wilson said he saw a clear increase in the number of monarchs heading south during the annual migration.

"We tagged 1,050, which is more than we've ever tagged before," he said, "Some days were the largest numbers we saw tagging along the Bay of Fundy."

But by the time the butterflies arrived in Mexico last fall, it was clear something had gone wrong.

The colonies were less than half the size of the previous winter, at 2.83 hectares, a big disappointment for the people working to protect them.

We're going to lose this migration unless we can slow down these greenhouse gases.- Chip Taylor, director of Monarch Watch

Chip Taylor is the director of Monarch Watch and professor emeritus of ecology and evolutionary biology at the University of Kansas.

He has been trying to figure out what factors decide a good or bad year for the monarch butterfly.

And, in order to do that, you have to understand the migration process.

A late-summer monarch leaves New Brunswick for Mexico in August or September and flies the whole 4,200 kilometres or so.

Arriving in late fall, it huddles together with others in giant masses to conserve energy, heat and moisture.

At this point, it already has outlived a typical monarch butterfly.

When temperatures begin to warm in spring, it leaves the colonies and heads for the southern U.S., seeking milkweed to lay its eggs. Once that is accomplished, it dies.

Its offspring continue the journey north, also laying eggs to create another generation.

That will continue every four-to-six weeks.

The late-summer monarch that hatches in New Brunswick to make the return migration is quite possibly a great-great-great-great-great grandchild of the monarch that made the trip the previous year.

Taylor said in a phone interview there are events in that life cycle that can have a major effect on success or failure.

"If the March temperatures in Texas are really high, and they have been for many, many years recently, butterflies move too far north too soon," Taylor said.

"The potential effect of that is you move your eggs  —your offspring — into areas where the temperature is cooler and it takes them longer to develop."

Taylor said the effect is the same as humans choosing to wait until they're in their 30s to have babies: the population growth slows.

Heat is the culprit?

"High March temperatures are responsible for most of the declines," Taylor said.

He said the two other major factors are droughts in the late summer, as the monarchs need moisture and nectar to make the trip, and a slow migration due to warm temperatures in the fall.

He said this past year, the U.S. saw both a drought and a slow migration, about two weeks later than normal, and that combination was something Taylor hasn't seen in 25 years.

So, he's not surprised the population has decreased significantly.

And, since all three of the major factors he mentioned are consequences of climate change, he's not optimistic about the future. 

"The consequences aren't going to be good for the monarchs," Taylor said. "We're going to lose this migration unless we can slow down these greenhouse gases."

What we cold lose

Wilson is interested to see what effect this will have on New Brunswick's population come tagging season this year. 

Recently, Wilson hosted a group of Indigenous people at the tagging station in Point Lepreau.

One man asked if he could tag a butterfly in memory of his sister. Wilson agreed and helped as the man took on what was clearly a sacred task to him.

"He was very emotional, wrote down the number and the name, and asked if I'd let him know if it was ever reported to us."

Wilson had one of his own tagged monarchs show up in Mexico, in the very sanctuary he and his wife had visited years earlier.

He calls that visit "the most awesome natural history experience we've ever encountered."

Wilson said approaching the site on the wooded trail, they began to see a few monarchs flitting about. The numbers increased as they got closer, and when they finally reached the location of the swarms, "the air was full of butterflies."

The giant fir tree limbs were weighed down with the swarms. Wilson said the boughs can sometimes break under the strain.

And, he suddenly noticed something about the members of his party.

"Within 15 minutes, we were all whispering."

Like you would in a church.