The Swainson's Warbler is "one of the most secretive and least observed" birds, experts said. View Full Caption Barbara Rubinstein

CENTRAL PARK — A bird that's been called one of the most secretive and least seen on the continent is wowing birders in Central Park.

The Swainson's Warbler was spotted Thursday and has drawn roaming crowds of excited bird watchers hoping to catch a rare glimpse of the migrating songbird.

Barbara Rubinstein, 69, managed to spot it Thursday.

"He sang. Every once in a while, he'd give a call, a little note. He's very plain, but subtly beautiful with a lovely call," Rubinstein said.

The warbler usually spends its summers in the southern United States and winters in the Caribbean, experts said.

Cornell University's Lab of Ornithology calls the Warbler "one of the most secretive and least observed of all North American birds."

"If it weren't for its loud, ringing song, the presence of the species in many areas would go completely undetected," according to the Lab's website.

Birders even came from upstate to see the avian rarity, like Roddy Greaves, 64, who drove more than two hours from Kingston Friday — but hadn't spotted it by midmorning.

"I've been a birder since I was 9 and have never seen one," he said.

"This is a rare bird that doesn't usually come this far north. It'd be a 'life bird' for me."