Some useful publications on wildlife viewing trends:

Birding in the United States: A Demographic and Economic Analysis, USFWS

2001 National and State Econmic Impacts of Wildlife Watching, USFWS

National Survey on Recreation and the Environment 2001: Current Patterns in Marine Recreation

1999 California Heritage Tourism Report

Sierra Nevada Heritage Tourist Resource List

Wildlife Viewers in the Western States PowerPoint ( 3.5 MB file)