This time it really is bye-bye Birds.

Nearly three years after ruffling some of its members' feathers with plans to sell a rare copy of John James Audubon's The Birds of America, the Providence Athenaeum is finally poised to go through with the sale. The so-called "double elephant folio" of 435 color engravings is due to be sold Thursday at Christie's auction house in New York City.

In its catalog for the sale, Christie's estimates that the Athenaeum's copy of Birds could fetch between $5 million and $7 million, although the final price could be much higher if bidding is brisk. (The current record for a comparable set of Audubon prints is $8.8 million, set in 2000.)

"Basically, we know where the low end of the market is for a full set of Audubon prints," said Frances Wahlgren, head of Christie's rare books and manuscripts department. "What we don't know, and won't know until the bidding ends on Thursday, is where the market's high end is."

Wahlgren, who will be the auctioneer at the 4 p.m. sale, said several factors make the Athenaeum's copy of Birds unique.

One is the history, or provenance, of the portfolio, which was purchased directly from Audubon himself in the mid-1830s and has been part of the library's collection ever since. Another is the fact that Audubon visited Providence in 1840 to meet with Athenaeum leaders.

"The condition of the prints is extremely good," Wahlgren said. "But the fact that the Athenaeum was one of the original subscribers to Birds of America, and that Audubon himself actually came to Providence to confer with Athenaeum members, makes it even more important."

For the Athenaeum, the looming multimillion-dollar payday represents a chance to tackle a host of problems, ranging from a shrinking endowment to long-deferred repairs to its headquarters on Benefit Street, in Providence.

"It's a chance to make a fresh start financially," said Athenaeum president Betty Rawls Lang. "While it's sad to lose such an important work, we really don't have much of a choice. The library's future is at stake."

At the same time, Lang acknowledged that the sale had already taken an emotional toll on the Athenaeum. In particular, she cited the impact of a lawsuit filed by a group of dissident members that sought to block the sale by accusing Athenaeum officials of fraud and mismanagement.

The lawsuit was eventually settled in the Athenaeum's favor (according to the judge, the dissidents "failed to offer even a scintilla of evidence" of illegality), but the constant bickering and bad publicity turned off even some Athenaeum supporters. It also led to the departure of executive director Jonathan Bengston, who left last year to take a job in Toronto.

"No question, this has been a difficult time," Lang said. "As long as there was a chance the lawsuit might be upheld, we really couldn't do much of anything. It wasn't just that we couldn't go ahead with the sale of the Audubon. We couldn't even do strategic planning for the next year."

Still, Lang insisted that the worst was over, citing, among other things, the arrival of a new executive director, Alison Maxell, in March. She also said membership was up and that she and Maxell had tried to reach out to current and former members who had opposed the Audubon sale.

"We've really tried to bring people back into the fold," Lang said.

Flighty market

A successful sale would certainly aid the healing process. But if anyone needs a reminder of how fickle the auction market can be, last week's sale of paintings from the New York Public Library provides a stark example of how even blue-chip artworks can fizzle on the auction block.

Though the sale was widely publicized -- and just as widely criticized -- some of its most important lots, including a portrait of George Washington by Gilbert Stuart and a smaller canvas by John Singleton Copley, either failed to sell or sold well below their pre-auction estimates.

In the end, the auction, held at rival Sotheby's, raised $15.6 million -- far short of the pre-auction estimate of $22 million to $31 million.

Asked about the Sotheby's sale, Wahlgren said some estimates had probably been too high. A high starting price, he said, tends to discourage the kind of bidding wars that can send prices soaring.

He also noted that Christie's had heavily promoted the Athenaeum sale, notably by producing a lavishly illustrated catalog ($30 at www.christies.com) and by holding pre-auction exhibits in California and Texas.

"We really hope that the collection stays in the public domain," Wahlgren said. "Since there aren't a lot of copies [of Birds] in public institutions out West, we thought buyers there might be interested in the sale."

A masterpiece

Ultimately, though, interest in the sale may hinge on something more basic: the sheer beauty of Audubon's masterwork.

Printed in London between 1827 and 1839, The Birds of America is a rare thing -- a great work of science that is also a great work of art. Even today, after Audubon's images have been widely reproduced in books and posters, the sight of one of the original hand-colored engravings can take your breath away.

Partly, it's the scale of the engravings, which are printed on special oversize sheets of paper that allowed Audubon to portray most of his subjects at something close to life size. (The term "double elephant" refers to these oversize sheets, which are roughly equivalent to large modern-day posters.)

But it's also the beauty of the individual sheets, each of which required the combined efforts of a team of inkers and engravers, under the supervision of Audubon and his printer, Robert Havell. As a result, each bird in the set, from the scowling Snowy Owl to the sinuous Blue Heron to the flaming American Flamingo, is a masterpiece.

Though Audubon and his heirs released several other editions of Birds, notably a smaller "royal octavo" edition in the mid-1840s, nothing approaches the scale and drama of the original double elephant folio.

"Every time we pull out one of the sheets to show people, the reaction is the same," Wahlgren said. "They're absolutely bowled over."