A good place to find out about existing and developing birding trails is via the American Birding Association. See this link: http://www.americanbirding.org/resources/birdingtrails.html
National Audubon Society supports birding trails and its many chapters often play large roles in birding trail success. See this link: http://www.audubon.org/bird_trails/index.html
Montana Birding and Nature Viewing
Montana Audubon Birding Hotline and State Bird List http://mtaudubon.org/html/birdwatching_state_bird_list_hotline.htm
Birding hotline phone number (weekly updates): 406-721-9799
Montana Bird Distribution houses information on where birds are found in Montana.
Montana Dept. of Fish, Wildlife & Parks Animal Field Guide
Montana Wildlife Viewing Guide: The binocular signs on Montana highways and the state map are linked to wildlife viewing sites listed in this guidebook.
University of Montana Avian Science Center (see birdwatching)
Audubon's Important Bird Areas (IBA's)
Important Bird Areas, or IBAs, are sites that provide essential habitat for one or more species of bird. IBAs include sites for breeding, wintering, and/or migrating birds. IBAs may be a few acres or thousands of acres, but usually they are discrete sites that stand out from the surrounding landscape. IBAs may include public or private lands, or both, and they may be protected or unprotected.
IBA's on the Bitterroot Birding and Nature Trail
Bitterroot River http://iba.audubon.org/iba/viewSiteProfile.do?siteId=2821&navSite=state
Blodgett Fire http://iba.audubon.org/iba/viewSiteProfile.do?siteId=2928&navSite=state
IBA's on the Missoula Birding and Nature Trail
View the list of all Montana IBA's