End of a reign?
Scientists point to habitat loss as main reason for decline in monarch butterflies
As technologically advanced as we are, and as many discoveries as we make each year about other planets, genetics and long-extinct species, there is at least one mystery humans have yet to solve—that of the monarch butterfly.
How, for instance, does one butterfly return to the roosting place of its predecessors five generations past? The migration pattern has long stumped scientists.
“The adults that come back to the overwintering sites are five generations removed. That’s one of the amazing things about monarchs—how do they know where to go?” said Sarina Jepsen, program director at the Oregon-based Xerces Society, which, among other things, monitors monarchs. “Nobody knows how they find the same trees, but they come back to the same sites every single year.”
Beyond its baffling migrations, though, the monarch holds a place in many hearts for its sheer beauty. Nothing seems to signal spring quite like the first sighting of those bright orange and black wings.
“The monarch is special. It is big and bright and connects with our sensibilities in a positive way,” offered Don Miller, an associate professor of biological sciences at Chico State. “It’s the butterfly that springs to people’s minds first when they imagine a butterfly—at least in North America.”
Unfortunately, the population of monarchs has hit a historic low. National Geographic reported in March that scientists who monitor the insects as they “winter” in Mexico had recorded an appreciably smaller group than in the past. This past winter they occupied an area 59 percent smaller than last year. In addition, Jepsen said the Xerces Society—named after the extinct Xerces blue butterfly, which called San Francisco home before its lush native habitat was destroyed—said results of an annual monarch count in California reveal a more than 80 percent decline since 1997.
Much of this is due to two factors, scientists agree—habitat loss and climate change.
“The numbers sound alarming, and they’re why we’re working on monarch conservation,” Jepsen said. “But I also have to urge caution. We’re confident the monarch is declining, but we aren’t ready to say they’re in danger of extinction.”
The monarch’s eastern territory lies mostly to the east of the Rocky Mountains, where they can be seen in huge numbers flying from their wintering grounds in Mexico all the way up to Canada. In California, the migration is a bit different—instead of flying north, the monarchs roost on the coast during the winter and make their way east. At the end of the year’s multigenerational cycle, they head back to the ocean.
“Monarchs really do stand out because of their powerful migration,” said Miller, a butterfly enthusiast who leads an annual local count of the insects for the North American Butterfly Association. While he does catch a glimpse of a monarch now and again, he said, “I’ve never seen them in appreciable numbers around Chico.”
The migration may be awe-inspiring, but the life cycle of the monarch is no less magical.
A tiny egg laid on a milkweed plant hatches into a caterpillar, or larva. The caterpillar feeds on the milkweed leaves until it’s nice and plump, and then, sensing that it’s time for a makeover, spins a silky cocoon in which it “sleeps” for about 10 days. When it emerges, it’s not a caterpillar that appears, but a vibrantly colored butterfly. That butterfly then flies north—or, in California’s case, east—to find a milkweed plant on which to lay its eggs.
So, what happens when milkweed plants are hard to find? What happens when trees formerly used as roosts during the winter have been replaced by apartment complexes?
“In the West, development is a huge issue,” Jepsen said. She pointed to 27 sites in California that, according to the Xerces Society, were former monarch hotspots taken over by development, and at least three more that are threatened by it. An even bigger cause of habitat loss across the country, however, is the increased use of genetically modified organisms.
“As monarchs are flying throughout the U.S., it’s important that they be able to find milkweed,” she said. “Historically, a lot of milkweed would crop up in corn and soy fields, and on crop edges. But now that growers have these new GMO crops that are ’Roundup-ready,’ they’re able to spray their whole crop and quite easily wipe out anything that is not their crop. It’s led to a lot less milkweed across the landscape.”
Individuals across the country have taken it upon themselves to plant milkweed—it’s available at Floral Native Nursery in Chico, Miller said—to offer monarchs a place to reproduce. That’s one way ordinary citizens can help out.
Climate change affects the monarch in California by way of drought. The drier the year, Jepsen said, the fewer monarchs her group has counted in its annual Thanksgiving monarch census in the Golden State. In addition, she said, “The predicted changes in climate expected to happen in the next few decades likely will create a climate that is not suitable for the type of tree where monarchs roost in Mexico.”
The monarch is not currently on any endangered species list. In fact, Jepsen said they probably exist in the millions, mostly on the East Coast. And, by both Jepsen’s and Miller’s accounts, the monarch occupies no great link on our ecological food chain. (In fact, they are poisonous to most predators—something they owe to the milkweed plant they eat as a caterpillar—and are extremely bitter-tasting.)
But most people would agree that the monarch, with all its beauty and mystery, is special.
“Butterflies are by far and away the most charismatic, the most appealing of invertebrates,” Miller said. “They make us appreciate the natural world, and they make us want to take steps toward trying to preserve it.”