Birding in the United States: A Demographic and Economic Analysis
http://library.fws.gov/Pubs/birding_natsurvey06.pdf
Identifies who birders are, where they live, how avid they are, and what kinds of birds they watch. Also provides an economic measure of birding, including how much birders spend and the economic impact of these expenditures. From the U.S. Fish and Wildlife Service.
