What is a double elephant?

"It is now a month since my work was begun by Mr. Lizars; the paper is of unusual size, called 'double elephant', and the plates are to be finished in such superb style as to eclipse all of the same kind in existence." - J.J. Audubon, December 10, 1826

And 'eclipse all' he did! No other ornithology prints could measure up to Audubon's - literally!  As indicated above, the term 'double elephant' refers to the unusual (double) size of the paper used by Audubon and his engravers (Havell followed Lizars) for the original "Birds of America." The untrimmed paper measured a gargantuan 29 1/2 x 39 1/2 inches! Officially, the proper English measurement for double elephant paper is 40 x 27 inches - untrimmed. Elephant paper is a bit smaller, measuring 28 x 23 inches untrimmed. 

Why such a large (double) size? Audubon insisted that each bird be depicted life-size. When you consider the immense proportions of subjects such as the Brown Pelican or of the White Pelican or the American Flamingo, the necessity of choosing 'double elephant' paper becomes obvious.

But to this, Audubon himself adds ...

"Merely to say, that each of my illustrations is of the size of nature, were too vague ... Not only is every object, as a whole, of the natural size, but also every portion of each object. The compass aided me in its delineation, regulated and corrected each part, ... The bill, the feet, the legs, the claws, the very feathers as they project one beyond another, have been accurately measured." John James Audubon. Ornithological Biography, Volume 1