[It's not easy to photograph small insects in flight--even harder than photographing bats.]
LAWRENCE, Kan. — Pinching a bright orange butterfly in one hand and an adhesive tag the size of a baby’s thumbnail in the other, the entomologist bent down so his audience could watch the big moment.
“You want to lay it right on this cell here, the one shaped like a mitten,” the scientist, Orley R. Taylor, told the group, a dozen small-game hunters, average age about 7 and each armed with a net. “If you pinch it for about three seconds, the tag will stay on for the life of the butterfly, which could be as long as nine months.”
Dr. Taylor, who runs the Monarch Watch project at the University of Kansas, is using the tags to follow one of the great wonders of the natural world: the annual migration of monarch butterflies between Mexico and the United States and Canada.
The northward migration this spring was the biggest in many years, raising hopes of butterfly enthusiasts throughout North America. But a drought in the Dakotas and Minnesota meant that not nearly as many butterflies started the return trip. And without the late-summer hurricanes that normally soak the Texas prairies and sprout the nectar-heavy wildflowers where the monarchs refuel, many are presumably finding that leg of the journey a death march. Dr. Taylor has already halved his prediction for the size of the winter roosts in central Mexico, to 14 acres from 30.
Nevertheless, the 4,000-mile round trip made by millions of monarchs holds a central mystery that Dr. Taylor and a network of entomologists are trying to solve.
The butterfly that goes from Canada to Mexico and partway back lives six to nine months, but when it mates and lays eggs, it may have gotten only as far as Texas, and breeding butterflies live only about six weeks. So a daughter born on a Texas prairie goes on to lay an egg on a South Dakota highway divider that becomes a granddaughter. That leads to a great-granddaughter born in a Winnipeg backyard. Come autumn, how does she find her way back to the same grove in Mexico that sheltered her great-grandmother?
Wildebeest, in their famous migration across the Serengeti, learn by following their mothers — or aunts, if crocodiles get Mom. But the golden horde moving south through North America each fall is a throng of leaderless orphans.
Birds orient themselves by stars, landmarks or the earth’s magnetism, and they, at least, have bird brains. What butterflies accomplish with the rudimentary ganglia filling their noggins is staggering.
They are one of the few creatures on earth that can orient themselves both in latitude and longitude — a feat that, Dr. Taylor notes, seafaring humans did not manage until the 1700’s, when the clock set to Greenwich time was added to the sextant and compass.
All monarchs start migrating when the sun at their latitude drops to about 57 degrees above the southern horizon.
But those lifting off anywhere from Montana to Maine must aim themselves carefully to avoid drowning in the Gulf of Mexico or hitting a dead end in Florida. The majority manage to thread a geographical needle, hitting a 50-mile-wide gap of cool river valleys between Eagle Pass and Del Rio, Tex.
To test their ability to reorient themselves, Dr. Taylor has moved butterflies from Kansas to Washington, D.C. If he releases them right away, he said, they take off due south, as they would have where they were. But if he keeps them for a few days in mesh cages so they can see the sun rise and set, “they reset their compass heading,” he said. “The question is: How?”
The skill is crucial because of storms. For example, 1999 was a banner year for monarchs on the East Coast; they were blown there by Hurricane Floyd.
Dr. Barrie Frost, a professor of neuroscience at Queens University of Canada, is fairly certain that they don’t use the earth’s magnetic field or the sky’s polarized light. He builds butterfly flight simulators, big barrels open to filtered sunlight with an airflow that a butterfly must navigate with a tiny wire glued to it. Computers sort out the random flitting to say which direction they were aiming for. Repolarizing the light or flipping the magnetic field with a coil does not redirect them, he said.
Dr. Frost believes that sun reckoning launches the monarchs generally only to the south, while mountain chains and the Gulf of Mexico funnel them toward southern Texas.
But once in Mexico’s mountains, they gain elevation and make several sharp turns. Dr. Frost suspects that they are guided by the smell of the previous year’s corpses.
Dr. Taylor disagrees. Butterflies don’t have the odiferous fatty acids that would survive for a year, he said. Disputing the “funneling” theory, he points out that the butterfly biologist William H. Calvert has shown that most monarchs cross central Texas, and his own work has shown that a monarch tagged near the Atlantic or the gulf is only one-tenth as likely to reach Mexico as one tagged in the Great Plains.
“If you end up along the coast, you’re toast,” Dr. Taylor said.
The bad news about this year’s migration may be temporary, but butterflies also face longer-term threats.
Jeffrey Glassberg, president of the North American Butterfly Association, remembers much bigger flocks as recently as the 1980’s. “The whole coast of Staten Island turned orange with butterflies,” he said.
Global warming is shifting the seasons for the wildflowers. New herbicide-resistant strains of corn and soybeans are letting farmers kill off more milkweed patches. Monarch caterpillars eat only milkweed, which contains a poison that makes birds retch. Just like the bright colors of poison frogs, the monarch’s glowing orange markings warn predators that they will regret their dinner.
To get more milkweed sprouting and to support his research (“it’s terrific data, but it’s bankrupting me, and we’re not in a part of the country where philanthropy is easy to come by”), Dr. Taylor sells packets of seed for what he calls monarch way stations. He has recruited people to create nearly 1,000 way stations since April, in private gardens, golf courses, schoolyards and city parks.
The tagging event for families here was part of a much larger effort. Dr. Taylor gives out more than 150,000 numbered tags each year to butterfly enthusiasts from the Rockies to the Atlantic (West Coast monarchs have separate migratory routes). In winter, he goes to the Transvolcanic Mountains in Mexico and spreads the word that he will pay $5 for each one found. That amount, about half a day’s pay for a laborer, is enough to make families spend hours sifting piles of dead butterflies beneath the fir trees where the monarchs roost, semidormant in the chilly fogs at 10,000 feet.
The biggest threat to the migration, said Lincoln P. Brower, a biologist at Sweet Briar College and one of the world’s foremost monarch experts, is the steady attrition of forests because of illegal logging.
Although the Mexican government turned 366,000 acres into a butterfly sanctuary, it has failed to protect them. Convoys of trucks laden with old firs worth $300 each are a common sight on the roads; nearly half the preserve has been logged since 1984.
“It’s unconscionable,” Dr. Brower said. “It’s like mining the Old Faithful geyser for its gypsum. If it isn’t stopped, I’m afraid the whole migration will unravel.”