Recordings of the distinctive double-rap sound of ivory-billed woodpeckers, which scientists once believed were extinct, were posted on the Internet yesterday in a further demonstration that the scarce bird is probably alive and well in Arkansas forests.

The ivory-bill, the world's third-largest woodpecker, has a 30-inch wingspan, a jet-black body, large white wing patches and a prominent red crest. The recordings of the staccato taps and a "toot" call like a tin horn are similar to sounds made by the rare woodpecker, researchers at the Cornell Lab of Ornithology said in a statement.

Once known as the "Lord God" bird for the exclamation provoked by its dramatic appearance, the ivory-bill was believed extinct until an announcement in April that a team had documented its presence in Arkansas wildlife refuges. One hundred double-knock sounds were identified after 18,000 hours of recordings were analyzed, researchers said at a meeting of the American Ornithologists Union in Santa Barbara, Calif., yesterday.

Not all were convinced. "Extraordinary claims require extraordinary proof," Jerome Jackson, a biology professor at Florida Gulf Coast University in Fort Myers, said in an e-mailed statement from the meeting. "In my opinion we haven't seen it yet."

John Weaver Fitzpatrick, director of the Cornell Lab, said in an interview from the conference: "This bird has this mythic position in natural history in North America. The idea that we could bring it back, and bring back that forest with it, is an idea that has a lot of power with Americans -- that we haven't completely blown it."

One recording may have included "two birds, possibly responding to each other," said Scott Simon, director of the Nature Conservancy in Arkansas, in a telephone interview. The recordings can be heard at www.birds.cornell.edu.

A team will resume the search for more evidence of the rare bird on Nov. 1. It will be led by the Cornell Lab, which is part of Cornell University, and will include the Nature Conservancy, a nonprofit preservation group; the U.S. Fish and Wildlife Service; the Arkansas Game and Fish Commission; and other partners.

The Big Woods Conservation Partnership is managing the search for the rare woodpecker, while federal agencies lead the endangered species recovery team.

A stuffed male and female ivory-billed woodpecker in a Louisiana museum. They were thought to be extinct.