Attendance at US National Parks is declining

According to a 2006 study funded by The Nature Conservancy, per capita visits to US National Parks have been declining since 1988, after 50 years of increase prior to that. The key factors accounting for most of the decline included:
Source: Pergams, O.R.W. & Zaradic, P.A. (2006). Is love of nature in the US becoming love of electronic media? 16-year downtrend in national park visits explained by watching movies, playing video games, internet use, and oil prices. Journal of Environmental Management 80: 387-393. See also http://www.nature.org/success/art18259.html