The sites, in 10 states, have been closed since Oct. 1 because of the partial government shutdown.
The agency said Friday that despite limited staffing, allowing public access to Waterfowl Production Areas on wildlife refuges will not cost any money or jeopardize public safety.
North Dakota Gov. Jack Dalrymple had threatened to sue unless lands in his state were opened.
Dalrymple says pheasant hunting should begin as scheduled this month. He says a government shutdown is not legal justification to close unstaffed, public lands.
The decision opens hunting areas in 10 states: North and South Dakota, Montana, Minnesota, Iowa, Wisconsin, Michigan, Nebraska, Idaho and Maine.