On 16 March 1934, President Franklin D. Roosevelt signed the Migratory Bird Hunting Stamp Act, which requires an annual stamp purchase by all hunters over the age of sixteen. The stamps are created on behalf of the program by the US Postal Service and depict wildlife artwork chosen through an annual contest. They play an important role in habitat conservation because ninety-eight percent of all funds generated by their sale go directly toward the purchase or lease of wetland habitat for protection in the National Wildlife Refuge System.[citation needed] In addition to waterfowl, it is estimated that one third of the nation's endangered species seek food and shelter in areas protected using Duck Stamp funds.[citation needed]

Answer this question, if possible (if impossible, reply "unanswerable"): What does the Act require all hunters over the age of sixteen to do?
an annual stamp purchase