The Big Duck is a ferrocement building in the shape of a duck located in Flanders, New York, on Long Island. It was originally built in 1931 by duck farmer Martin Maurer in nearby Riverhead, and used as a shop to sell ducks and duck eggs. It was added to the National Register of Historic Places in 1997. It is a principal building on the Big Duck Ranch, listed on the National Register of Historic Places in 2008.