After the sale, Tollemache described the early 19th century four-volume, double elephant folio work, which was estimated at £4m-6m, as "priceless" .
The final sum exceeded the record for a printed book, the premium-inclusive $8,802,500 (£5,565,110) paid by Sheikh Saud al-Thani of Qatar in March 2000 for a different copy of Birds of America, sold at Christie's New York.
The Audubon was part of the sale of Magnificent Books, Manuscripts and Drawings from the collection of Frederick, 2nd Lord Hesketh, which in total realised £15m including premium.
Audubon's quest to record all of America's birds in their natural habitats started in the 1820s, but it took him over a decade to find them, and the birds were often shot in order for him to paint them.
After Audubon sank $115,000 into the project, the book was eventually published in Britain in 1838.
Measuring 3ft 2in x 2ft 2in (97 x 65cm), the illustrated volumes contained 435 hand-coloured plates, each a skilled depiction of a different bird - some life-size - and cost subscribers $1000.
It is not an especially rare book, as of the under 200 copies thought to have been produced, 119 are known to survive today. However, only a handful remain in private ownership.
Sotheby's buyer's premium is 25/20/12%
By Anna Brady