Birders buy stuff. Feeders, bird seed, binoculars and other optics, bird books, magazines, outdoor clothing, etc. We travel to see birds, staying at hotels, eating in restaurants, and supporting convenience stores with bathrooms. We visit local, state and federal parks.
The US Fish and Wildlife Service issued a report on July 15, 2009, with the Press Release titled, "Birdwatchers No Featherweights in Contributions to the Economy," which documents the $36B economic impact of the birdwatching hobby in the US. In addition to the demographics on birdwatching, there is a report on other wildlife watching. Hopefully, these reports will give impetus to preserving these fascinating creatures.
What I don't get is why TX is not in one of the top 5 states for the percentage of birdwatchers when we have such a bonanza of birds here.