It’s only been spotted once before in the U.S. Now birders are flocking to Maine to spot a rare hawk.

It’s a sight that experts say has only been witnessed one other time in the United States, but now some lucky birders are heading to Maine to see a rare raptor that’s turned up in Vacationland: the great black hawk.

Doug Hitchcox, a staff naturalist for Maine Audubon, posted a “rare bird alert” on Wednesday, announcing that the great black hawk had been photographed in Biddeford two days before.

He said the news “shocked the bird world.”

“Don’t bother grabbing your Sibley guide, as this bird isn’t in there,” he wrote. “It really wasn’t on anyone’s radar as a possibility in Maine (let alone the U.S.).”

Perseverance pays off: pic.twitter.com/dAmXaTDJTx

— Doug Hitchcox (@dhitchcox) August 9, 2018

The hawk, which is native to Central and South America, was spotted for the first time in the U.S. this spring on South Padre Island, Texas, according to Hitchcox.

The naturalist said it took a few days for news of the Maine sighting to get out, but by Wednesday morning, about a dozen birders descended on the area where the hawk was seen: in a pine on the west side of a pond north of Lily Pond Road.

Hitchcox said he didn’t see it that morning, but when he returned after work, he spotted it.

“As luck would have it, after an hour of looking, I managed to track down the bird! The word was spread — and fortunately a group of birders were able to see the bird before it went to roost around 7:45 p.m.,” he wrote.

Birders have traveled from as far away from Arizona to try and catch a glimpse, The Portland Press Herald reports.

Tom Graham, of Seabrook, New Hampshire, arrived Thursday. He told the newspaper more people are likely on their way.

“By this Saturday there will be hundreds,”  he said. “They’ll be driving or flying here. This place will be packed. You could make $1 million if you had a bus to bus them all in.”

Seth Davis is in the running for “Dad of the Year” after ticking Great Black Hawk without even needing to put his baby down. pic.twitter.com/pTb6aHnxpO

— Doug Hitchcox (@dhitchcox) August 9, 2018

The naturalist told the Press Herald that it remains a mystery how the hawk ended up in Maine, so far from its territory. Each year, he said, birders usually spot three or four birds that haven’t previously been seen in the state.

“We get rare birds, but not on this scale,” Hitchcox said. “I think this is one for the record books.”