qnli question: What does land has Federal Duck Stamp money helped purchase? sentence: Since 1934, the sale of Federal Duck Stamps, a required purchase for migratory waterfowl hunters over sixteen years old, has raised over $700 million to help purchase more than 5,200,000 acres (8,100 sq mi; 21,000 km2) of habitat for the National Wildlife Refuge System lands that support waterfowl and many other wildlife species and are often open to hunting.