The Audubon Society's tribute to John James Audubon's Birds of America (originally published between 1827 and 1838) features all 435 of Audubon's vibrant, beautiful portraits of the birds he studied, along with his notes on their behaviors and other characteristics (the site also includes audio samples of each bird's call).
The collection can be sliced in many ways: chronological, alphabetical or by state.
The illustrations are gorgeous, and the hi-rez scans are enormous — 11,000+ pixels wide!
John J. Audubon’s Birds of America [Audubon Society]
(via Open Culture)