American artist and naturalist John James Audubon published The Birds of America in the first half of the 19th century, and his massive “double-elephant” folio of life-size bird illustrations remains one of the most ambitious nature books ever produced. On June 14, a rare edition of the four-book set is hitting the auction block, and it's expected to fetch up to $12 million—more than any Audubon book ever sold.

This edition of The Birds of America was owned by the dukes of Portland from around 1839 to 2012. Because it was stored on the shelves of the family's Nottinghamshire, England estate for nearly a century, the set's prints of watercolor drawings have remained remarkably well-preserved.

In 2012, the copy was auctioned off to philanthropist and businessman Carl W. Knobloch, Jr. for nearly $8 million. Knobloch donated the books to the Knobloch Family Foundation (KFF) before his death in 2016. Now, the KFF is sending the books to auction once again. This time, all proceeds of the sale will go to nature conservation.

New York City auction house Christie's describes the set in a listing as "among the finest copies in private hands of this icon of American art, and the finest color-plate book ever produced." Each of the 435 double-elephant folio pages measures 39.5 inches by 26.5 inches, the largest sheets Audubon could get his hands on at the time, and they feature 1037 birds from 500 species. The books are bound in red Moroccan leather with gold detailing on the borders and spines. The four-volume set also comes with the Ornithological Biography, a collection of five books describing the specimens in The Birds of America and their habits.

Christie's estimates the set will sell for $8 million to $12 million when the final bid is placed later this month. To date, the most expensive copy of The Birds of America was a first edition acquired from Sotheby's in London for $11.5 million. That sale also broke the record for the most expensive printed book ever sold at auction, a record held until 2013.

All images courtesy of Christie's