(AP) — Hundreds of national wildlife refuges that provide critical habitat for migratory birds and other species are crippled by a staffing shortage that has curtailed educational programs, hampered the fight against invasive species and weakened security at facilities that attract nearly 50 million visitors annually, a group of public employees and law enforcement said Wednesday. The refuges, as well as 178 other federally protected areas dedicated to waterfowl habitat and wetland preservation, attract 47.5 million visitors a year for bird-watching, hunting, fishing and educational activities, but their primary mission is the preservation of critical habitat for fragile species. Many, but not all, are in remote areas. Because they are focused on wildlife preservation, refuges are less well known by the public than their flashier, selfie-friendly cousins at the National Park Service, yet they have expanded rapidly in recent years as funding has shrunk. Since 2010, the overall refuge budget dropped by $17 million to $486 million while the system added more than 700 million acres, said Houghton.