9 books in series

National Audubon Society Field Guides

National Audubon Society Field Guides is a 9-book series with 9 primary works first released in 1977 with contributions by National Audubon Society, John L. Bull, John Farrand, Charles W. Chesterman, Kurt E. Lowe, Richard Spellenberg, Elbert L. Little, Lorus Johnson Milne, Margery Milne, Mark R. Chartrand, Jane Friedman, David McWilliams Ludlum, and Peter Alden.

The Audubon Society field guide to North American trees
National Audubon Society Regional Guide to New England (National Audubon Society Field Guide to New England)
The National Audubon Society field guide to North American birds.
National Audubon Society field guide to North American wildflowers : western region
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National Audubon Society Field Guide to the Southeastern States

National Audubon Society Field Guide to Rocks and Minerals: North America
National Audubon Society Field Guide to Insects and Spiders: North America
Field Guide to the Night Sky
National Audubon Society Field Guide to Weather: North America