The Monarchs Are Back. Or Are They?

Monarch butterflies seem to be on the rebound, but they still face serious threats from surprising sources.

by L. Clark Tate
Photos by Jordan Plotsky

Oct. 9, 2014—They’re back! At least we think they are. While many burnt-orange beauties are already flitting energetically through the Natural Bridges State Beach Monarch Grove, it’s too early to tell just how many monarch butterflies will return to overwinter along our shores. But the butterflies did arrive on time, beginning around Sept. 1, and there is reason for optimism as we gear up for Welcome Back Monarchs Day this weekend: Last year the population rebounded for the first time since the year 2000, peaking at 7,500 individuals, an increase of 7,000 over the dismal winter of 2012. And that’s in spite of the local Steller’s jays having developed a taste for monarchs (more on this later).

The improvement locally is kind of a big deal, but it’s just one tiny piece of a nationwide puzzle. Twenty-six major sites host monarchs through the winter in California, including Pismo and Pacific Grove. Then there’s the whole Midwest/East Coast contingent.

Butterflies born on the west side of the Rocky Mountains winter on the California coast. Those on the east side head south to the mountains of Central Mexico in a storied migration of around 2,500 miles. As Martha Nitzberg, lead naturalist at Natural Bridges says, “The Great Divide really is the Great Divide”—mostly. New evidence suggests the two populations do a little mingling.

But does that mean last year was a great one for eastern monarchs as well? Not at all. According to the World Wildlife Fund (WWF), the population reaching its winter resting grounds in Mexico last fall was the lowest since recordkeeping began in 1993. And though the numbers have been looking pretty dire since 2004, the steeply plummeting trend over the past four years shook monarch lovers everywhere.

The Numbers
Millions of individual monarchs swoop down to Mexico each year. So many, in fact, that scientists measure the population in acres of forest covered. WWF’s data shows that, in 1993, the first year on record, 15.4 acres of trees were dripping with wings. Ten years later, in 2003, it was 27.5 acres. Then there was the incredible winter of 1996,when a full 45 acres boasted the winged wonders. Last year? In 2013, only 1.6 acres of forest housed the flagging butterflies.

What happened? Experts cite the following four reasons, or some combination of them, for the eastern population’s free-fall.

The Catch All: Climate Change
The whole point of the monarch migration is to avoid bad weather. The picky insects seek out dense canopies to keep them warm (rather like a blanket), moisture in the air to guard against large temperature swings (water holds heat) and large tree stands, or those protected by the landscape like Santa Cruz’s bowl-shaped Monarch Grove, to block the wind.

Climate swings can cause bad weather to show up unexpectedly. In 2002 an intense winter storm took out 80% of the population resting in Mexico, according to Scientific American.

Shifting temperatures can also mess with migration patterns. The fall migration is largely tied to shortening day length—more or less a constant. What triggers the return trip northward, however, is a different story. Scientific American reports that warming temperatures prompt the butterflies to follow the trail of flowers northward as they bloom—but only after they are exposed to the cooler mountain temperatures in Mexico. If a period of cold weather never occurs, the butterflies never turn north.

Similarly, drought conditions reduce the population of milkweed—the only plant upon which monarch eggs are laid, caterpillars reared and chrysalises formed. These are kind of crucial to monarch persistence.

Here’s something else that cuts back on milkweed stands: Plowing up tons of grassland and drenching agriculture fields in herbicide.

Soybeans and Corn: Bad for Butterflies
The Farm Bill, that massive piece of legislation that drives everything from crop subsidies to agricultural conservation, has historically sparked many an unforeseen side effect. The most recent bill, signed into law in February and ringing up at $956 billion, incentivizes the planting of corn and soybeans, as does the Environmental Protection Agency’s Ethanol mandate, according to High Country News.

These policies lead to sod busting, or plowing up grasslands, a practice that actually releases climate-changing carbon into the atmosphere. It’s happening at a rate comparable to rainforest destruction. It also, you guessed it, decimates the local milkweed populations.

Dr. Chip Taylor, a professor at the University of Kansas and the director of Monarch Watch, ays habitat loss is the gravest threat the butterflies face, and calls for restoration of up to 1.5 million acres of milkweed habitat.

Marvelous Monsanto: Kills Bugs Dead
But milkweed doesn’t just grow in untouched grasslands. It’s a weed. It can grow in and around fields and along disturbed soils, like roadways.

Enter Monsanto with its Roundup Ready System. Monsanto genetically engineered corn and soybean to tolerate elevated levels of herbicide, specifically its own Roundup weedkiller. Slate reports that as of 2013 83% of corn and 93% of soybeans in the U.S. were herbicide-tolerant. Then Monsanto sold everybody a bunch of Roundup.

Between the subsidies and the herbicides, milkweed declined 58% in the Midwest between 1999 and 2010. During that time monarch numbers dropped by the same figure: 58%.

Predators and Backhoes
Just in case global warming and milkweed lose don’t take the monarchs down, Santa Cruz Steller’s jays and habitat loss are waiting in the wings.

It seems Santa Cruz’s Steller’s jays are a bit smarter than most. According to Nitzberg, the notoriously clever corvids developed a taste for the toxic monarch last winter. Possibly taking a cue from the monarch-munching chickadee, the birds learned that while the body and wings of a monarch are made out of bitter milkweed (i.e., the same cardiac glycoside toxins that the caterpillar ate before metamorphosing), its fat stores, made up of the pollen eaten by the adult butterfly, are not. The jays now jump on a branch to shake loose a cloud of monarchs, snatch one by a wing and—avoiding all but the fatty stores—feast.

Loss of critical winter habitat in Mexico and unprotected California lands is also a long-term concern.

“This whole thing in the Midwest is really scary,” sums up Nitzberg. But the trend looks familiar. “In the ‘90s what’s happening in the Midwest happened to us,” she says. That is, numbers started plummeting. She’s fielding a lot of questions lately from folks in the Midwest and East. What should they do?

Find places to plant milkweed, is the short answer. Recently a campaign to plant milkweed between grape arbors in the Central Valley went really well. Nitzberg credits that campaign with upping monarch numbers by 7,000 last year. And while we won’t get this year’s official California count till after the overwintering “peak,” sometime just before Thanksgiving, she’s optimistic.

Chip Taylor is also predicting an improvement in the population hanging out in Mexico for the winter based on mid-season monitoring and good weather. Numbers could increase by 2 to 4 percent. As he told NPR, that’s a good indication that these tough little lovelies are capable of making a comeback.

So go plant some butterfly-friendly plants! Not milkweed, though—it does not naturally occur along the coast—Nitzberg and some folks in the scientific community worry that catching a whiff of the plant may stir up mating hormones too early in the season. Maybe leave the milkweed to the folks in the Central Valley.

“I think that monarchs are the advocates for all the butterflies,” muses Nitzberg. “They are the biggest and the brightest.” If we can’t keep this native plant pollinator around, which one will be next?