Twenty-five miles south of Baltimore, in a grassy pen enclosed by two rows of fences, electrified to provide protection against raccoons and monitored by video cameras, a pair of the tallest birds in North America emerge from their hut.

Powder-white, all neck and legs, they step through the rain with care, as if in high heels.

For 15 years, staffat the Patuxent Research Refuge near Laureltookan unusual approach to raising endangered whooping cranes: They dressed in crane costumes to teach the chicks to eat like cranes and to drink like cranes. It was elaborate theater to save a species at the brink of extinction.

But something was wrong.

Once released in the wild, the stately birdsabandoned their eggs. The speckled chicks died. Researchers lost hundreds of cranes — eggs that failed to hatch, chicks thatdied — since the project began in 2001. Theytried costumes and puppets; they flew ultralight airplanes to lead the migrating cranes south.

It turned out they couldn't teach parenthood.

“We still can't do better than Mother Nature,” said Brian Clauss, the flock manager.

In January, federal wildlife officials decided to end the theater. They scrapped the ultralight-led migrations and scaled back the costumed rearing of chicks “to put emphasis on more natural methods of rearing and releasing whooping cranes,” thepublic-private Whooping Crane Eastern Partnership said.

Now spring approaches, and with it the first eggs will be laid in a popular experiment that's changed course.

The whooping crane project has been describedas a model of conservation. But after years of research comes anacknowledgment: Some of nature's complexities still lie beyond reach.

Whooper home

The Patuxent refuge — nearly 13,000 acres of marsh and woodlandsat the western edge of Anne Arundel County — was founded 1936 by President Franklin D. Roosevelt as the firstfederal reserve devoted to wildlife research.

Signs of its history linger today, such as the fenced plots where earthworms tested positive for DDT decades after the pesticide was applied. In 1969, Patuxent researchers linked DDT to the thinning of birds' egg shells, a discovery that led to the pesticide's ban to protect bird populations.

The first whooping crane, a one-winged male named Canus, arrived in 1966. When he was rescued, the U.S. Geological Survey says, he was one of only 42 whooping cranes left in the wild. Named for the cooperation between Canada and the United States to save the species, Canus went on to sire many of the whooping cranes hatched in captivity.

Breeding efforts expanded in June 2001 with the whooping crane reintroduction project.

The U.S. Fish and Wildlife Service launched the project to raise and train a new population of cranes to be released into the wild for migrationfrom Wisconsin to Florida — fertile grounds for cranes. Patuxent would raise the chicks.

Success would be a milestone in wildlife conservation: There has never been a successful crane reintroduction, said Peter Fasbender, the lead Fish and Wildlife Service biologist on the project.

Soon came documentaries, fan clubs, even “wild for whoopers” swag.

Whoopers are white with black wingtips and yellow eyes.Their wingspan can reach 71/2 feet.Standing, a grown crane canstare a researcher in the eye. They will eat mice and acorns, berries and blue crabs.

Whooping cranes mate for life. When breeding, the male climbs on the female's back and flaps for balance. So clipped wings mean birth control.

As many as 20,000 whooping cranes roamed North America before humans interfered, according to the National Wildlife Federation. Their white feathers became high fashion in women's hats. They were targeted by commercial hunters and sold for meat. Wetlands were drained. Power lines were raised. A 1941 count foundonly about 20 birds.

In February last year, the Fish and Wildlife Service counted 603 whooping cranes. But theyremain rarer than giant pandas.

At Patuxent, it worries Clauss how closely the chicks follow him. He's afraid of stepping on one.

“It's a little precarious in the beginning,” hesaid.

Whooping cranes typically lay two eggs at a time. Steal the eggs, and they lay two more. In this manner, researchers can coax six eggs from a pair.

That's too many chicks for the pair to raise. Also, siblings fight. The stronger chickkills the weaker.

So each spring at Patuxent, Clauss and several other “crane technicians” become surrogate parents to about 30 chicks. Theywear white frocks and hoods to conceal their shape, so the birds don't become dangerously comfortable among people.

“When it does see a human after it's released, it will be afraid,” Clauss said.

At hatching, the birds are 5 inches tall and gangly. Clausscarries a puppet crane head, plays recorded crane calls, and never speaks a word. He's Mom.

To teach drinking, he splashes the puppet beak in a water dish. The chick imitates.

For eating,he pokes the puppet head in pellet food. The chick tries.

He leads them on walks; they follow at his boots. He intervenes in fights and soon they outgrow their hostility.

“You're trying to shape their little minds,” he said. “It's a big responsibility.”

Next, the chicks are introduced to ultralight airplanes. Costumed pilots drive a grounded plane around a pen. A mechanized puppet head drops mealworms as the chicks follow.

Come fall, the young cranes are crated and flown to swampy Necedah National Wildlife Refuge in Wisconsin. Then they fly behind the ultralight to refuges on Florida's Gulf Coast. After one trip, they remember the route and migrate unassisted the next year. Planes lead only each new class of cranes.

The January decision changes it all.

“We're no longer going to do the ultralight release,” said Sarah Converse, a research ecologist at Patuxent. “We're also moving away, to the greatest degree possible, [from] any costume rearing.”

Problems surface when the grown chicks mate in the wild.

Some abandon their eggs. Others abandon their chicks. Alone, the offspring are eaten by crows, snakes and raccoons.

What's broken?

So the whooping crane reintroduction project presents a troubling question: What's broken in the cranes?

Swarms of black flies are driving some birds from their nests, but researchers suspect a deeper problem.

“There's something about these birds' early-learning experiences that affects their breeding,” Converse said. “For example, you're cared for by your parents and you learn something that we can't really teach because we don't know it. It would take us a long time to understand the intricacies.”

Over the years, Patuxent researchers searched and studied, but failed to pinpoint the missing lesson. Since the project began in 2001, the researchers have releasedabout 300 whooping cranes. The cranes havehatched 64 chicks in the wild. Only nine havelived to fly.

“We're meaningfully far from where we need to be,” Conversesaid. “The only problem in the whole lives of these birds is from laying eggs to fledgling chicks. If we could just fix that period, if we could just fix those couple months — April to October — we would be successful.”

Federal wildlife officials say the reproductive failure was reasonto end the old methods.

The decision was reached at a meeting in Wisconsin of the Whooping Crane Eastern Partnership, a group of federal and state agencies and nonprofits working to restore cranes.

Nearly 100 cranes migrate from Wisconsin to Florida each year, but they fail as parents. The partnership's goal is to build a self-sustaining flock.

“While survival of the birds is something we are proud of, a critical lack of reproductive success has hampered the partnership's effort to meet its goal,” the partnershipsaid.

Two other flocks exist. About 40 cranes live year-round in Louisiana. Another 300 migrate from Canada to the Gulf Coast of Texas.

Thatflock has almost two-thirds of the world's whooping cranes. The concentrated population remains vulnerable to various threats, such as an oil spill or a hurricane. One disaster could wipe out most wild whoopers.

“That's why people worked so hard to introduce another population,” Converse said.

Without airplanes, puppets or costumes, captive cranes at Patuxent will raise their own chicks until fall. Then juveniles will be shipped to Wisconsin to follow other migrating cranes.

The researchers say thenew methods will produce about 25 percent fewer chicks. At Patuxent, Converse hopes for a dozen this spring.

So researchers are betting these fewer chicks will grow to be better parents.

They say it will take five years before they know.

tprudente@baltsun.com