Fri August 30, 2013
Wise Old Whooping Cranes Keep Captive-Bred Fledglings On Track
Originally published on Fri August 30, 2013 11:40 am
Being a wildlife biologist in the 21st century increasingly means rescuing rare animals from extinction. Among the success stories is the whooping crane. Seventy years ago there were only about 16 birds left on the planet. Now there are about 600.
But breeding more birds isn't enough. Scientists want to restore the crane's way of life, too. And a team of ecologists at the University of Maryland have discovered something that suggests they are succeeding: Captive-bred whoopers are picking up tips from older birds about how to skillfully navigate south for the winter.
It's a sign that those whooping cranes are passing knowledge from one generation to the next and, in a sense, rebuilding their culture, scientists said Thursday in the journal Science.
How birds navigate over vast distances during migration has long been something of a mystery. Scientists aren't sure how much is innate and how much is learned, or how much is based on landmarks, stars or even the Earth's magnetic field.
But the country's small population of whooping cranes has provided a clue.
Many of the whoopers in the world were born in a wooded wilderness 20 miles from the U.S. Capitol, at the Patuxent Wildlife Research Center in Maryland. Patuxent is a hidden gem, a pocket of wilderness surrounded by highways, suburbs and government compounds.
As I approached one adult whooper in a fenced enclosure on a recent visit, the bird let loose with a raucous, prehistoric screech — a call that's both distinctive of its species and a bit spine-tingling.
"This is the closest I've ever been to a whooping crane," says Greg Smith, who runs Patuxent. The birds are usually a little more skittish, he says.
The big whooper stands 4 feet tall, has snow-white feathers and seems a bit ungainly — yet elegant in its long-legged, mincing walk. A couple of brown-feathered 1-year-old birds peer up from the adjacent pen and peep at us.
Smith is with the U.S. Geological Survey, which runs Patuxent. He says the research center is sort of the Noah's Ark for endangered animals. The whoopers we see are full-time residents at Patuxent, so we're allowed to approach them.
But nearby, through the woods, is a labyrinth of fenced enclosures holding scores of young whoopers that will be released to the wild. Fabric screens secured to the fence keep them from seeing us. That's so the birds won't become accustomed to us, Smith says. "The more fear they have of humans, the better off we think their survival chances are," he says.
But the cranes can sense us. Had there been a roof over their enclosure, they would have raised it with their calls.
Whooper eggs from around the country are brought here so biologists can hatch the eggs and raise the birds. People who work with new birds wear white coveralls and hoods to look less human-like and more whooper-like. They even use whooper puppets to mimic adult birds. "They show the young birds how to peck at food," Smith says.
But here's the weirdest part: Workers drive around the enclosures in an ultralight, one-person aircraft ... that moves along the ground. It's the first step in teaching these birds to identify an ultralight aircraft as a mature whooper. Then when the birds are yearlings and it's migration time, they're shipped up north, to Wisconsin.
"The ultralight in Wisconsin not only circles on the ground and teaches them to follow," Smith says, "but it also ultimately lifts up into the air" and accompanies the whooping cranes on their great migration, which lasts between 50 and 100 days.
Every year a batch of youngsters follows an ultralight aircraft, flown by a group called Operation Migration, down to Florida. After that first migration, the birds are able to find their way south each year without following a plane. One trip is enough to learn the way — sort of.
Scientists have been watching cranes migrate on their own for a dozen years. Eventually, they noticed something peculiar. Some groups of whoopers flew along a nice, tight route. But others tended to drift off the ideal migration route, sometimes 40 or 50 miles away.
That's not good. The birds use more energy when they stray from their route, and they don't end up in the safest places for roosting and finding food.
When scientists compared the straight-arrow cranes to the wanderers, it appeared there was only one difference between them: an experienced bird.
"If there was one older bird in the group, they would fly more accurately," says ecologist Thomas Mueller at the University of Maryland.
He and his colleague William Fagan came to that conclusion after ruling out other hypotheses. For example, they knew the pedigree of each bird, so they could check whether more closely related groups did better. That would suggest some genetic, instinctual ability was at work. But being related didn't matter. And larger groups didn't do better than smaller groups.
The only thing that seemed to improve performance, Fagan says, was having at least one experienced bird along. And the older the bird got, the better the group flew.
"It's amazing," Fagan says, "in the sense that it's a concrete demonstration of an animal's ability to learn and how that learning can be refined over time."
Now, of course you can teach many animals — your dog, your horse — all sorts of things. Even a mouse can learn to run a maze in a lab. Adult birds teach their young to fly. Chimps teach their offspring how to dig for termites.
But in the whooping crane's case, younger birds learned first from humans, then from older birds. And the birds got better at it every year. "There is cultural learning that is an improvement in a very large scale process ... migration in over 1,000 kilometers distance," Fagan adds.
Exactly what the cranes are learning isn't clear. Patuxent ecologist Sarah Converse suspects they're spotting landmarks along the migration. But what's most important, she says, is that the whooping cranes are learning anything at all from their elders.
We're talking about a species that's now totally bred and raised by humans, she says. These fledglings don't know squat about whooping crane life in the wild. "We're actually trying to restore not just a biological population but a culture," she says. "So there's a knowledge that whooping crane populations have that they pass on amongst individuals — not just genetically, but [through social] learning."
If the whooping cranes are learning a complex skill from each other, Converse says, maybe they can learn to reproduce better in the wild — something the birds are pretty terrible at right now. But they need to figure this out if they're going to make a true comeback.
LINDA WERTHEIMER, HOST:
Being a wildlife biologist in the 21st century means, increasingly, rescuing rare animals from extinction. Among the success stories is the whooping crane. Seventy years ago, there were only 16 of these birds left on the planet. Their habitat had disappeared, and they were hunted for their feathers. Now there are about 600.
But breeding more birds is not enough. Scientists want to restore the crane's way of life, its culture. NPR's Christopher Joyce reports on a discovery that suggests the cranes are learning to do that themselves.
CHRISTOPHER JOYCE, BYLINE: Many of the whooping cranes in the world were born in a wooded wilderness 20 miles from the U.S. Capitol.
GREG SMITH: This is the closest I've ever been to a whooping crane.
JOYCE: They seem sort of curious.
SMITH: They are.
(SOUNDBITE OF WHOOPER CALLING)
JOYCE: An adult whooper lets loose, as Greg Smith and I stand just outside its chain-linked enclosure. Nearby, brown-feathered one-year-olds peep. The adult is four feet tall, snow white and elegantly long-legged. Smith's a biologist and heads the Patuxent Wildlife Research Center in Maryland. A short walk through the woods leads to a labyrinth of fenced enclosures holding scores of whoopers.
Fabric screens on the fencing keep them from seeing us. That's so they won't become accustomed to humans.
SMITH: The more fear they have of humans, the better off we think their survival chances are.
JOYCE: Whooper eggs from around the country come here. Biologists hatch and raise the birds. Workers wear white coveralls and hoods and use whooper puppets to mimic adult birds. Then, the weirdest part is someone drives around the enclosures in an ultralight, one-person aircraft on the ground. The birds think it's an adult crane.
Then they ship the yearling birds to Wisconsin, where another ultralight plane awaits.
SMITH: The ultralight in Wisconsin not only circles on the ground and teaches them to follow, but also ultimately lifts up into the air and makes this great migration of between 50 to over 100 days to Florida.
JOYCE: This yearly migration was created by a group called Operation Migration. After the first time, the birds migrate all on their own. But after a dozen years of this, scientists noticed something unusual. Some groups flew a nice, tight route. But others drifted 40 or 50 miles off the ideal migration route, and it appeared there was only one difference between the straight-ahead flyers and the crooked ones: an older bird.
THOMAS MUELLER: If there was one older bird in the group, they would fly more accurately.
JOYCE: Thomas Mueller is an ecologist at the University of Maryland. He and ecologist William Fagan found that migrating groups with lots of genetically related birds didn't do any better than unrelated birds. So, apparently, it wasn't some innate genetic skill at work, here. Fagan adds that as the birds got older, their flying group got better.
WILLIAM FAGAN: It's amazing in the sense of it's a concrete demonstration of the animal's ability to learn, and how that learning can be refined over time.
JOYCE: Now, of course, adult animals do teach their young chicks to fly, chimps to dig for termites, all sorts of life skills. But Fagan says this is more unusual: younger birds learning a very complex skill, first from humans, then from unrelated older birds. And that skill improves.
FAGAN: Here is cultural learning that is an improvement in a very large-scale process, that is migration in over 1,000 kilometers distance.
JOYCE: The researchers published their findings in the journal Science. They suspect there is some innate ability involved in crane migration, too, but clearly, doing it well is learnable. Exactly what they're learning, well, they don't know for sure. Patuxent ecologist Sarah Converse suspects it's landmarks along the way. But Converse says the really important thing here isn't just navigating better. It's that birds bred and raised by humans are learning from each other how to be, well, real whooping cranes.
SARAH CONVERSE: We're actually trying to restore not just a biological population, but actually a culture. So there's a knowledge that whooping crane populations have that they pass on amongst individuals - not just genetically, but learning.
JOYCE: Converse says if the birds can refine migration skills, maybe they can learn something else they've forgotten: How to reproduce better in the wild. They're pretty terrible at that right now. They'll need to be better if they're going to make a true comeback. Christopher Joyce, NPR News. Transcript provided by NPR, Copyright NPR.