How do you train an eagle to fly?

With strong arms, patience and lot of leather clothing.

“They really don’t appreciate what we do for them,” said Janice Constable, a volunteer for the University of Minnesota’s Raptor Center, cradling a young eagle like a baby as it jabbed angrily at her gloved hands. “Really they don’t.”

This year the center’s volunteers have had their work cut out for them. The number of sick and injured eagles brought in for care totaled 153 birds as of November, far more than average.

“And it’s not even our busy eagle season,” said Julia Ponder, the center’s veterinarian.

The busy period comes now, during deer hunting season, because the birds are frequently poisoned by lead shot they eat while scavenging deer entrails and carcasses left behind by hunters. The season produces about one-third of the center’s eagle patient population each year.

It’s not clear yet what’s driving this year’s higher numbers — everyone at the center has been too busy taking care of birds to sit down and analyze the data. Ponder did say it’s not just a reflection of what could be Minnesota’s growing population of eagles. The increase in patients, up from an average of 114 or 117 birds per year, is much too high for that, she said.

About half the eagles arriving at the center die within a day or so because their injuries are so traumatic. That’s typical for most wild bird species, said Lori Arent, the center’s clinical director. Of the eagles that survive, 80 to 90 percent are eventually released back into the wild, she said.

And for young birds in their care, that will be soon. They need to be ready when the state’s wild eagles start to gather around open stretches of the Mississippi River in early-to-mid December as they do every year.

That’s when the orphans can learn, from their own kind, the finer arts of fishing and scavenging.

“We can’t teach them how to hunt here,” said Arent.

But Arent and the volunteers can teach them how to fly. Though really, the sessions at Como Park in St. Paul are more a strength-training regimen for birds that have been weakened by illness or injury and are living in a cage.

Last week, Constable and two other volunteers were working with a golden eagle, a rarity for the center, which had arrived from the Mankato area more than a year ago with a badly broken wing and broken leg. The leg healed pretty easily, but the wing needed three surgeries, including the use of a bone-bonding agent that is experimental in animals.

It’s been a long road for the male bird. At first, Constable said, it would just sit on the ground. Then it started taking a few hops and stretching its massive brown wings. Then it flew a few feet, anchored to a human by a long line tied to its feet.

As of last week, the eagle was swooping across the grass Como Park all the way to the end of its 300-foot tether.

“Wow, that was a great flight,” said Steve Masten, another volunteer, as the bird landed underneath a tree on the far side of the ball field.

But Constable noticed that the bird was still veering slightly to its right as it flew, a sign that it was not ready to be released.

“They have to be in top shape to survive in the wild,” she said.

Lactic acid

After years of research and experimentation with the birds, the Raptor Center wildlife experts have training down to a science. From blood tests that measure lactic acid, they’ve learned that an eagle’s muscle strengthening peaks after eight flights in one session. After that, the birds tire out. So now there is a routine. Three mornings a week volunteers drive from the center on the St. Paul campus holding the birds on their laps — with a firm grip on the taloned feet — and not quite sure what they would say if stopped by the police.

Once at the park, volunteers take turns tossing an eagle into the air, so each bird gets a rest while the other flies.

The volunteers get some exercise too, as they walk the length the line to where the bird sits in the grass. They gently hang the bird upside down with the line while they gather its feet and scoop it back into their arms. They are exceedingly careful to protect their feathers and to keep their powerful curved beaks at arm’s length.

“They’ll go right for your face,” said Arent.

Arent said volunteers will continue to train a bird as long as it makes progress. The golden eagle, for example, continues to get stronger. But if it’s not ready after two years, it will probably never be ready for the wild, she said.

Those with damaged feet or wings, heart disease caused by lead poisoning or other permanent disabilities are sent to wildlife centers around the country as education birds, she said.

But for trainers, the joy comes at the moment of final release.

“The one I released, you could tell, ” said volunteer Larry McMains. “He’s flying away, he stops to glide for a while, and he realizes that nothing’s going to happen. Then he just flew like crazy.”