Here is a compilation of some of the research materials that we have found very useful.

Useful Books:
Beginner’s Guide To Bats By: Kim Williams, Rob Mies, Donald & Lillian Stokes
Birds of Michigan Field Guide by Stan Tekiela – This is a very cool pocket sized book focused on only Michigan. I LOVE this book!
Stokes Nature Guides A Guide to
Bird Behavior Volumes I, II & III by Donald Stokes — These books are different from your average bird books. They actually cover a reduced number of species in very great detail as to the behaviors, patterns, calls, displays and habitat.  Very interesting, but not for the field
Peterson Field Guides Eastern Birds by Roger Tory Peterson — This is my standard go to book.
Peterson Field Guide To Animal Tracks by Olaus J. Murie
National Audubon Society Field Guide to Insects and Spiders Very interesting guide. You cannot always identify the species, but usually at least the family of insects.
Peterson Field Guides Trees and Shrubs by George A. Petrides
Peterson Field Guids Wildflowers: Northeastern/North-Central North America by Roger Tory Peterson & Margaret McKenny

Useful Websites:

Toadily Toads Everything about the care of toads!
Lady Bird Johnson Wildflower Center
A great site with tons of pictures of wildflowers and information on the wildflowers in your area.