LONDON - It's quite a nest egg. John James Audubon's "Birds of America," a rare blend of art, natural history and craftsmanship, fetched more than $10 million at auction on Tuesday, making it the world's most expensive published book.

With its 435 hand-colored illustrations of birds drawn to size, the volume is one of the best preserved editions of Audubon's 19th-century masterpiece. The sale at Sotheby's auction house had been anticipated for months by wealthy collectors.

The book sold for $10,270,000 (6.5 million pounds) to an anonymous collector bidding by telephone, the auction house said.

Because each picture is so valuable, there have been fears the volume will be broken up and sold as separate works of art. However, experts believe that's unlikely. The tome is probably more valuable intact. And collectors hold Audubon in such reverence that the notion of ripping apart a perfect copy would be akin to sacrilege.

"Audubon's 'Birds' holds a special place in the rarebook market," said Heather O'Donnell, a specialist with Bauman RareBooks in New York. "The book is a major original contribution to the study of natural history in the New World."

"It's also one of the most visually stunning books in the history of print: The scale of the images, the originality of each composition, the brilliance of the hand coloring."

Then there's the wow factor.

"No one can rival John James Audubon for frontier glamour," O'Donnell said. "The story of his lonely journey through the American wilderness and his struggle to record what he saw there gives the 'Birds' a resonance that no other book can match."

Part naturalist and part artist, Audubon possessed an unequaled ability to observe, catalog and paint the birds he observed in the wild. Experts say his book, originally published in 1827, is unmatched in its beauty and is also of considerable scientific value, justifying its stratospheric price tag.

Pom Harrington, owner of the Peter Harrington rarebook firm in London, said it has been 10 years since the last complete edition of "Birds of America" was auctioned, going for a then-record $8.8 million.

He said it is unusual to find a copy not in a museum or academic institution.

"If you want to buy an example of a rare work of art, this is one of the best," he said. "It is valuable in its artistic nature because it is so well drawn."

He said other historic books - such as an excellent example of a Gutenberg Bible - would likely be valued even higher if they came up for sale.

Harrington estimated that a complete Gutenberg Bible in good condition would probably sell for between $30 million and $50 million, but none has been sold in more than 30 years.

In recent years, he said, a complete First Folio of Shakespeare's works sold at auction for about $5.6 million while a Chaucer collection sold for more than $4 million.

"That's getting close to Audubon," he said.

While the Audubon volume holds the record for a published book, a 72-page notebook of Leonardo da Vinci's handwritten notes and illustrations went for even more. Known as the Leicester Codex, the collection was bought by Bill Gates in 1994 for $31 million.

Also on the block Tuesday was a Shakespeare First Folio from 1623 that fetched $2.05 million (1.3 million pounds).

Sotheby's books expert David Goldthorpe said the Audubon and Shakespeare volumes represent "the twin peaks of book collecting." Both came from the estate of the 2nd Baron Hesketh, a collector who died in 1955.

The "Birds of America" plates were printed in black and white and then hand-colored by "the best artists of the time," Harrington said. The collection, made from engravings of Audubon's watercolors, measures more than 3 feet by 2 feet (90 centimeters by 60 centimeters) because Audubon wanted to paint the birds life size.

The size of the illustrations makes them extremely valuable as stand-alone pieces of art, leaving the complete edition vulnerable to being broken up so the prints can be sold one by one. Harrington said the wild turkey depicted in the first big plate of the book can be sold for $200,000.

But Mark Ghahramani, a rarebook specialist at Classic Bindings in London, said it is unlikely this "Birds of America" will be divided up.

"There are very few copies left of the entire book, so I would think that whoever bought it at the auction would be quite interested in keeping it whole," he said. "Anything to do with American natural history is quite valuable."

Audubon, who died in 1851, represents a unique figure in American history - a Renaissance man with shades of Huckleberry Finn. Like Mark Twain's fictional character, Audubon made an epic voyage down the mighty Mississippi - but with a scientist's inquisitive nature.

Taking along only a rifle, an assistant and a drawing pad, he made illustrations of as many birds as he could find.

He did not find a printer in the United States willing to take on the book with its oversize illustrations, so he sailed to Britain, eventually finding printers in London and in Edinburgh, Scotland.

The volume is seen as a vital piece of American history, Harrington said.

"It is the most important natural history book for America," he said. "That is the main point. It screams Americana. For an American patriot, it is the greatest book on American heritage. There is no competition."