Hunting is available at more than 400 units of the National Wildlife Refuge System (national wildlife refuges and wetland management districts) and almost 20 national fish hatcheries. Hunting can be a habitat management tool to keep wildlife populations in check. Hunters' purchase of Duck Stamps helps buy conservation lands and is one of several ways hunters support conservation. All hunters must possess valid state hunting licenses. Be sure to also check regulations for each state and FWS location when planning your hunt.