Monarch butterflies gather on Long Island as part of epic migration

With a deft move of his net, 12-year-old Bear Graf, of Middle Island, captured an energetic male monarch butterfly, distinguishable by the two dark marks on his hind wings. He delivered him to the staff at the Jones Beach Energy & Nature Center to be tagged with a tiny numbered sticker delicately placed on his wing.

Graf was one of about two dozen children and adults stalking butterflies on Tuesday among the purple asters, spotted knapweed, and seaside goldenrod that grow in profusion in the sandy beachside soil, as part of an international monarch monitoring project.

Monarch butterflies gather in early fall by the dozens or hundreds along the South Shore, searching for late-blooming wildflowers in the daytime, roosting together at night, waiting for a breeze that will help carry them southwest. Each congregation will join millions of others that departed from elsewhere in the United States and Canada east of the Rockies, navigating distances of up to 3,000 miles to their winter sanctuaries in the cloud forests of central Mexico.

Monarchs are the only butterfly species in the world that makes such an epic migration.

After a journey of several weeks, they arrive in the mountainous states of Michoacán and Mexico, where they pack together so densely that the branches where they roost droop under their combined weight.

These overwintering colonies have been in decline in the past 20 years and scientists fear monarchs and their extraordinary migration are in danger. Experts have identified a number of reasons that fewer butterflies are reaching Mexico, any one of which is harmful but together could be catastrophic.

But experts and advocacy groups said there are also things people along the route, including those on Long Island, can do to help.

Brief lifespans, then a long, mysterious journey

A refresher from your grade school days: Monarchs begin their life cycle as tiny eggs laid on a milkweed plant. The larvae eat that host plant, and nothing else, shedding their skin several times as they grow into chubby caterpillars. They split one last time to form a chrysalis — jade green and flecked with gold — and emerge a week or two later as an orange and black butterfly, perhaps the most recognized member of the lepidoptera order of insects.

The adults feed on flower nectar, but survive just a few weeks, at least for the first three or four generations. They emerge, reproduce and die over the summer, but the butterflies that unfurl in late summer enter a different phase, called diapause. Their reproductive cycle is halted and they live up to nine months, long enough to travel south in fall.

Indigenous people of Michoacán celebrate the annual return of the monarchs in late October, which coincides with the Dia de Muertos festival, welcoming them as symbols of the visiting spirits of their relatives.

In the spring, the overwintering colonies begin the return trip, laying eggs along the way. The third and fourth generations finally complete the journey, some stopping in the Midwest or along the Eastern Seaboard, others continuing as far north as southern Canada, from Saskatchewan to Nova Scotia.

The research group Monarch Watch tries to keep track of their travels with its tagging program: If someone spots a butterfly with a sticker — usually when it is found dead — they can report the find, adding to the group's data on migration routes, timing and mortality.

Exactly how these insects, which weigh about half a gram, manage to navigate to the same spot in Mexico every year — a place they have never seen — is still not fully understood. But researchers have discovered that they possess a neural compass that sets their direction according to the position of the sun. They also can sense the Earth’s magnetic field — a backup technology for very cloudy days — and when they get closer to their destination, some scientists believe they may steer toward the scent of the fir trees.

Millions of monarchs spend the winter in these fir forests, but there are fewer now than there were decades ago, according to annual surveys that measure the number of hectares the monarchs occupy there. (Counting hectares is easier than counting individual butterflies across their whole geographical range.)

Through the 1990s, monarch populations varied each year, increasing and decreasing, depending mainly on the season’s weather conditions. But beginning in the early 2000s, monarch numbers began an unmistakable downward trend, and scholars have identified a number of reasons for the decline.

Storms, cars, pesticides among causes of decline

An increasingly volatile and warming climate is one cause of the decline, according to one recent study. Their winter habitats have shrunk as parts of the oyamel fir forest have been felled in illegal and legal logging operations.

Monarchs infected with the parasite Ophryocystis elektroscirrha, which has been spreading in recent years, often emerge deformed from the chrysalis; or else they are too weak to complete a migration, the University of Georgia's Project Monarch Health reports.

Some evidence, including the data collected by Monarch Watch, shows that the populations in the northern breeding range haven’t declined as much as those in Mexico, which suggests that they may be dying during the migration. Andy Davis, a research biologist at the University of Georgia, believes the largest cause of mortality is car collisions: He estimated that 25 million monarchs are hit or run over every year during the fall migration.

Monarchs’ dependence on one plant also makes them vulnerable. Milkweed was once ubiquitous in American prairies and woodland edges, and was still fairly common as those prairies were plowed under for farm fields, persisting alongside the rows of corn and soybeans.

But that changed with the widespread adoption of genetically modified crops, engineered to withstand heavy spraying with herbicides, Karen Oberhauser, a conservation biologist at the University of Wisconsin, explained in an interview. The wild milkweed that grew in the field margins and hedgerows had no such defense, and as the milkweed withered, monarchs lost tens of thousands of acres where caterpillars once hatched and grew fat.

"All of that habitat was gone," Oberhauser said. Now there are still good years and bad years, "with weather-driven changes, but much lower than they were two decades ago."

The annual winter surveys by Mexican and U.S. conservation groups suggest "the eastern migratory population of the monarch butterfly ... declined by approximately 80% since the mid-1990s," Steve Papa, a wildlife biologist at the U.S. Fish and Wildlife Service, told Newsday.

There's no hard data on numbers on Long Island, according to John Turner, conservation policy advocate at Seatuck. An accurate count would be especially tricky since there are resident monarchs who lay eggs here, and others that pass through during the spring and fall, using it as a "migratory motel," he wrote in an email to Newsday.

But "from a long-term historical perspective, the resident population of the species has undoubtedly declined significantly," he added, "given the huge loss of habitat" where milkweed once thrived, including Hempstead Plains, the Shinnecock Hills grasslands and Montauk Moorlands.

Kevin Munroe, director of Long Island preserves at The Nature Conservancy, told Newsday: "In the six years that I've been on Long Island, I have observed a reduction in the amount of monarchs that I see migrating through here."

"Some years are better than others," he added, "but in general, there's a decline."

Efforts to save monarchs

Still, monarchs are benefiting from an international effort to prevent further losses.

The monarch reserve in Michoacán was named a UNESCO World Heritage Site and protects 70% of the overwintering population.

Last year, the U.S. Fish and Wildlife Service, after years of study, proposed to list the monarch as threatened under the Endangered Species Act, which would require preservation of monarch habitat. The agency gathered public comments but has not yet finalized the listing.

In an effort to safeguard local populations, the New York State Legislature last spring passed a bill that would help fund habitat restoration for monarchs and other pollinators on public and private lands. Gordon Tepper, Gov. Kathy Hochul’s Long Island press secretary, said in an email she "will review the legislation."

At the Jones Beach nature center, curious children and adults gathered to watch the staff carefully pull five captured insects from the nets and place stickers on their wings. One by one, the tagged butterflies were transferred to the hand of a child, where they paused briefly before leaping into the air. By the end of the month, a few may even find their way to the mountains of Mexico.