CAPE MAY POINT, N.J. — Gently clasping the wings, Betty Ross delicately touched the butterfly’s abdomen and instantly recognized the evidence for what it was: Clearly, it had just indulged in a banquet of nectar.

Not that gluttony would be an issue: The butterfly would tip the scales at under 0.02 ounces.

And it would need all the nectar it could drink. This was among the countless millions of monarch butterflies that would attempt to fly as far as 2,500 miles — with the Jersey Cape as a popular stopover site for some migrators — to join their peers in central Mexico to spend the winter in cool, but not frigid, mountains.

“It’s one of the most unique biological phenomenons on the planet,” said Orley R. “Chip” Taylor, who founded the National Monarch Watch program at the University of Kansas.

Despite advances in recent decades in understanding their pathways and inner compasses, so much about the peregrinations of these colorful, fascinating creatures, a rare migrating insect, remains shrouded in mystery.

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Why those particular locations in the Sierra Madres? Why does it take only one generation to get there, and multiple to make it back? And how does something 10 times lighter than a paper airplane somehow survive cold fronts, nor’easters, tropical storms, and nasty headwinds on a diet of plant nectar and without so much as a weather app?

“Certainly a lot will fail in the attempt,” said Mark Garland, director of the Monarch Monitoring Project at the New Jersey Audubon Cape May Bird Observatory, part of the Monarch Watch program, in which hundreds of thousands of butterflies have been “tagged” in an effort to track their itineraries.

But amazing numbers of them do make it. “It’s indeed remarkable,” said Garland.

And they’re likely “all traveling as individuals, but they’re often taking cues from the environment that bring them to the same places,” said Garland. He likened it to cars on the Schuylkill Expressway.

“They’re not all traveling as a convoy,” he said, “but they’re all there because it’s when they need to be traveling, and how they need to go to get where they’re going.”

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Monarchs do have one thing in common with expressway motorists: Sometimes they go nowhere. With headwinds from the south on Saturday, followed by crosswinds from the northwest on Sunday and Monday, weather-savvy butterflies were passing the time “nectaring,” he said.

About monarchs

This so-called super generation of butterflies that makes it to Mexico won’t return. After the warming sun tells them it’s time to head north in the spring, they will fly an indeterminate distance, mate, and lay eggs.

Caterpillars, or more properly larvae, will emerge, and suffice to say they don’t spend much time with the Inquirer Dining Guide.

For roughly two weeks they consume nothing but milkweed — an endangered lifeline for the species — before entering the chrysalis phase and magically emerging as mature butterflies, ready to resume an astonishing relay journey.

They will live only a few weeks, but before they die they will travel farther north and repeat the reproductive process.

It will take four generations for the butterflies to return to their summer habitats across North America, most at latitudes between Philly and northern New England. They will give birth to a super generation of monarchs that live eight to nine months and undertake those marathon migrations.

Why Cape May

The majority of migrating monarchs follow paths through the heartland, but Cape May is an important stopover site for monarchs that summer in the East. Having somehow survived the wind regimes of the Northeast, said Taylor, they constitute a hardy and elite group.

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On the very fingernail of the Jersey Cape, the observatory is an ideal launching pad for the journey. And with all its nectar-bearing flowers, as a rest stop it is considerably more appealing than, say, the Molly Pitcher Service Plaza on the New Jersey Turnpike.

They have come from as far as southeastern Canada, said Garland, but until 1998, no one was certain where they were headed.

Tag teams

Betty Ross affixes a small, numbered sticker atop a gingerly scraped circle on a butterfly’s wing. Ross, who lives in Ohio, migrates here in spring and fall to help with the tagging operation.

Since 1992, more than 100,000 have been tagged at Cape May, Garland said.

Overall, maybe 1% of all tagged butterflies will be recovered, said Taylor. But those are sufficient to at least roughly map out their routes.

The monarchs appear to head toward Florida. However, said Taylor, they need to jog inland before they reach the Florida peninsula if they want to have a chance of making it to Mexico.

Some of the Cape May visitors will have ended up traveling 80 days, Taylor said.

Flying high, and low

When the winds are strong, as they were for the last three days, the butterflies stay low to the ground and prefer sheltered areas to await better flying conditions.

Like hawks, they exploit warm, rising air and once airborne, they might be visible to the naked eye, or out of binocular range. At least one glider pilot reported seeing monarchs at 11,000 feet.

See them while they last?

While a true census of monarchs would be impossible, said Garland, samplings have shown that the Cape May population has held fairly steady.

But based on surveys in Mexico, the numbers are declining alarmingly — 90% since the 1990s, according to the National Wildlife Federation. That may be related to climate change, which would affect both the timing of migrations and the weather the butterflies encounter.

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But a major factor is the loss of grasslands to agriculture and development that has depleted milkweed crops. Since milkweed is the only thing caterpillars eat, “if there’s no milkweed, there are no monarchs,” says the U.S. Fish and Wildlife Service.

The migration cycles are timed for the availability of milkweed, which also infuses monarchs with a substance that is toxic to predators.

The loss of monarchs would be immeasurable, says Garland. “It’s a wonderful creature to teach about nature,” he said.

And he added that if an insect could be said to have charisma, it would be the monarch: “I’ve yet to run into anyone who doesn’t like monarch butterflies.”