Whooping cranes walk to the marsh after sunrise in September. The cranes have had trouble raising chicks to the fledgling stage. Credit: Tom Lynn Photography

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Fourteen years and more than $20 million into one of the most widely recognized wildlife reintroduction efforts in the country, whooping cranes continue to suffer from low numbers and are far short of establishing a self-sustaining population.

The biggest problem, say those involved in returning them to parts of their native range in the eastern United States, has been the failure of adult birds to raise chicks that fledge.

Still, experts see some progress. The cranes are producing eggs and chicks in captivity, and an army of handlers is learning how best to release the birds to the wild. And they are also gaining a keen insight into how best to manage a species that is slow to mature and has a preference for remote locations.

Crane organizations also have fostered wide public support for the 5-foot-tall bird, in part by drawing attention to a migrating technique in which young cranes learn the route from crane-costumed pilots and their ultralight aircraft.

In the latest annual report, the Whooping Crane Eastern Partnership writes that "no crane introduction has ever been successful," and reintroduction of wildlife populations previously wiped off the landscape is "extremely complex and fraught with challenges."

Whooping cranes are the tallest bird in North America, and until their return they were last recorded in Wisconsin in 1878 — victims of overhunting and the loss of wetland habitat.

Since 2001, nearly 250 cranes have been released into the wild in Wisconsin, according to publicly available figures.

But only 95 are currently living. Also, two — possibly three — cranes born this year have been seen in and around the Necedah National Wildlife Refuge, northeast of Tomah, where the reintroduction first began.

Only six chicks have hatched in the wild and survived to fledge, according to the crane partnership. This year, 13 cranes hatched in the wild — the most ever. But at least 10 are dead and thought to have been killed by predators.

In contrast, a western flock of cranes that spends the winter on the Gulf Coast of Texas and the summer in northern Alberta has not faced the same reproduction problems. The worry for the western flock has been a protracted drought in Texas, which poses a long-term threat to the birds.

The western population stood at 304 cranes in early 2014, according to the U.S. Fish and Wildlife Service.

'Not satisfied'

The problems in Wisconsin were what prompted managers to start reintroducing nonmigrating cranes in southwestern Louisiana in 2011. Now Wisconsin and Louisiana are forced to divvy up a limited number of chicks raised in captivity until the wild population, if ever, can become self-sustaining.

"We were hoping that the birds would be a little — no, a lot — more successful at hatching and rearing chicks," said Peter Fasbender, field supervisor in the Green Bay office of the U.S. Fish and Wildlife Service.

"I'm not satisfied with the productivity that is out there."

Fasbender is co-chair of the crane partnership, a group of public agencies and private groups overseeing the reintroduction of the migratory population that lives in Wisconsin but spends the winter in Florida and other Southern states.

The group includes the Wisconsin Department of Natural Resources and the Baraboo-based International Crane Foundation, the world's leading crane conservation organization.

Representatives of those groups said last week that while no deadline has been set, there have been discussions about how long the experiment should continue. The next three to five years should give the partners time to see if new strategies designed to improve the cranes' chances pan out.

"That doesn't mean if we don't see improvement in that time period, we're shutting projects down," said Wade Harrell, who worked for the Fish and Wildlife Service and is the U.S. coordinator of a U.S.-Canada whooping crane recovery team.

"The western population has increased by about 4% a year," Harrell said. "We would like to see this in the reintroduced populations — and we have just not."

Since 2001, the eastern population has been hurt by predators, birds flying into power lines and other mishaps.

In 2007, 17 first-year cranes flew to Florida, led by ultralights operated by Operation Migration, a private group that leads young cranes on their fall migration. But they were killed by a storm that surged through the Chassahowitzka National Wildlife Refuge in Florida.

Cranes are also periodically shot.

Last week, the Fish and Wildlife Service issued a statement asking the public to help dispel the myth of "white" or "albino" sandhill cranes.

In July 2013, researchers with the International Crane Foundation found a dead radio-tagged whooping crane in a Waupaca County wheat field. The crane had been shot. Matthew Kent Larsen, 28, of New London pleaded guilty in federal court in Green Bay for violating the Migratory Bird Treaty Act by killing a protected species.

Larsen told authorities he shot the crane because he thought it was an albino sandhill. Whooping cranes are white and sandhills are gray or reddish brown. Shooting either bird is illegal.

Swarms of black flies

The Fish and Wildlife Service estimates the cost of each whooping crane at $110,000, with dollars coming from public and private sources. Fasbender said there is no central accounting because funding comes from public and private sources. He estimated the total cost of bringing back whooping cranes at more than $20 million.

To date, the most nettlesome issue has been the inability of adults to produce birds that fledge. The problem has been tied to parental inexperience and the presence of swarms of black flies at Necedah that drive cranes off their nests.

But as the crane population grows older, the black fly issue has loomed larger, according to Barry Hartup, director of the veterinary services at the Crane Foundation.

"We believe it's been an impediment to successful reproduction," Hartup said.

Scientists experimented at Necedah with spraying a naturally occurring bacterium, Bacillus thuringiensis, to kill the flies in 2011 and 2012.

Hartup said one promising experiment is removing eggs from nests, which prompts cranes to renest later and lay more eggs when the flies are gone. The eggs taken by crane managers are used for the captive rearing program.

Also, chicks have been released since 2011 farther east at Horicon National Wildlife Refuge and the White River Marsh State Wildlife Area, where black flies don't appear to be as much of a problem.

Trying different strategies

Initially, first-year cranes learned the migration by following ultralight aircraft, a costly and labor-intensive effort, which crane managers said could eventually be phased out.

In 2005, a second strategy started: Raising cranes in captivity and then releasing chicks in the company of older whooping cranes to learn the fall migration route of older birds.

In both cases, the chicks are raised by white-costumed humans, to minimize the chance that young cranes imprint on humans. There are concerns that the lack of interaction between chicks and adult cranes might be a reason for poor parenting later in their lives.

In 2013, a third strategy began: Chicks are hatched and raised by adults in captivity and then released into the wild in the vicinity of adult whooping cranes, who take over the parenting.

"We are trying to move forward a more natural release technique where chicks are not around people as much and are around real, live whooping cranes more," Harrell said.

"We want to try, hopefully, to reduce more of that captive effect."