Clinton Nienhaus and Kristina Dexter have seen tens of thousands of raptors fly over during five years on staff (Nienhaus) or as a volunteer (Dexter) at Duluth's Hawk Ridge.

But what they experienced on Sunday was something the avid birders described as a once-in-a-lifetime event, something that induced - in Dexter's words - "bird tears."

The inspiration for those tears was a red-tailed hawk, in itself one of the more common raptors to pass through Duluth on its fall migratory journey - an average of more than 6,100 are counted. But the typical red-tailed hawk is mottled brown on top, Nienhaus said.

This hawk was almost completely white.

It wasn't an albino, Nienhaus said. Albinos have no pigmentation at all, not even in their eyes or feet. This hawk was leucistic, meaning anywhere from "one white feather or one little patch of white to birds that are nearly entirely white or entirely white," he said.

Leucistic red-tails are uncommon but not rare, Nienhaus said. He sees between three and five of them in a typical migratory season. Only one of them has been close to as white as the one seen on Sunday, he said, although even that's not unheard of. In fact, there's a similarly white red-tail that hangs out every winter in the Bloomington, Minn., area.

What made this an extraordinary birding moment was the fact that Nienhaus held the bird in his hands.

Frank Nicoletti, Hawk Ridge's banding director, had captured the raptor in his net around 1 p.m. on Sunday.

Hawk Ridge uses lures in the guise of injured birds to draw raptors to one of three different nets, which are used to humanely capture the raptors. The birds then are banded, measurements are taken and recorded and then they're released, all within 20 minutes, Nienhaus said. Sometimes, they're brought out to the public viewing area, where a visitor can donate money to Hawk Ridge for the privilege of releasing the bird.

Nicoletti, who has been banding birds for 30 years, had only captured one leucistic red-tail before, and that one had only a few white feathers, Nienhaus related. (Nicoletti couldn't be reached in time to comment for this story.)

The bird was brought to the viewing area, where Nienhaus held it and briefly discussed it with between 40 and 50 onlookers. It was a larger bird, Nienhaus said, meaning it was probably a female. It was also at least 2 years old. Red-tailed hawks in the wild can live into their teens.

Nienhaus particularly noticed that all eight talons were white. "The whole bird was cool, but those feet were just so different from what you (ordinarily) see," he said.

Dexter was struck by its symmetry, she said, with two red tail feathers and one dark feather on each wing.

Then Nienhaus handed the bird to her to be released, much to Dexter's surprise.

"It was a very breathtaking bird, but it was especially breathtaking for me because I've never released a bird before," Dexter said.

Once the hawk flew, the onlookers crowded around her, hugging her, with tears on their cheeks, Dexter said.

Bird tears.

"We always joke about how there's a thing in the birding world when you're as passionate as we are, and we call it 'bird tears,' " Dexter said. "And it's a real thing that we witness when other people find birds for the first time."

Both Dexter and Nienhaus described the encounter with the leucistic red-tailed hawk as a once-in-a-lifetime experience. They talked about it late on Monday afternoon, after warming up by drinking coffee. It was Nienhaus' day off, and it was gray, chilly and rainy outside.

Naturally, they had spent the day birding.

Hawk Ridge

Although the annual Hawk Weekend Festival was in September, naturalist staff and volunteers are on site from 9 a.m. to 4 p.m. daily through Oct. 31. Hawk Ridge is located on Skyline Parkway off of Glenwood Street. Learn more at hawkridge.org.