Visitors to federal wildlife refuges generate more than $2 billion a year in economic activity in the United States, helping to employ more than 35,000 people and produce about $343 million in local, state, and federal taxes, according to a new report being released Tuesday. The report by the Fish and Wildlife Service said recreational activities such as birding, hiking, and picnicking account for nearly 75 percent of total expenditures at wildlife refuges across the United States, while fishing and hunting account for about 28 percent of expenditures. According to the report, wildlife refuges drew 46.5 million visits in 2011, with three of every four visitors coming from outside the local area. Visitors generated $2.4 billion of economic activity, making refuges a major contributor to ecotourism. The report said refuge visitors pay for recreation through entrance fees, lodging nearby, and purchases from local businesses.