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In the United States, each state has primary responsibility and authority over the hunting of wildlife that resides within state boundaries. State wildlife agencies that sell hunting licenses are the best source of information regarding hunting seasons, areas open/closed to hunting, etc. Hunting of migratory birds such as ducks and geese is managed cooperatively by state fish and wildlife agencies and the U.S. Fish and Wildlife Service. Migratory waterfowl hunters must possess both a state hunting license and a Federal Migratory Bird Hunting and Conservation Stamp (Duck Stamp), and each hunter needs a Harvest Information Program (HIP) number for each state in which they hunt migratory birds.
Open season is the time of the year when a particular wildlife species is allowed to be hunted as per local wildlife conservation law. Each state creates laws and codes governing the season dates and species, based on a complex process including citizen input, a state fish and game agency or department, and often an independent game council. This process updates a game code for each state which outlines all rules and regulations including hunting seasons. In each of the 50 states, abstracts of the larger game code are then presented in the official state hunting regulations for that given year. Season dates are often timed to occur when the population is at its maximum. It avoids the peak breeding period when members of a species are particularly vulnerable, and avoids any disruption to mating, which may affect productivity.
Closed season is the time of the year during which hunting an animal of a given species is contrary to law.  Typically, closed seasons are designed to protect a species when it is most vulnerable or, sometimes, to protect animals during their breeding season.
The closed season is timed to prevent hunting during times of peak reproductive activity, impaired flying ability during moulting (of game birds such as waterfowl), and temperature extremes, low population levels and food shortage.
A closed season is enforced by local conservation law for the conservation of the species and wildlife management; any hunting during closed season is punishable by law and termed as illegal hunting or poaching.