Ducks are neither mammals nor amphibians. They are birds. Ducks belong to the class Aves, which includes all birds. Birds are characterized by feathers, the ability to lay hard-shelled eggs, and the presence of a beak with no teeth.
Mammals, on the other hand, are animals that have hair or fur and produce milk to feed their young. Amphibians are a class of animals that live both in water and on land, and they typically have moist skin and lay eggs in water.
Ducks have feathers, lay eggs, and have beaks, which are all characteristics of birds. They do not have the traits that define mammals or amphibians. Therefore, ducks are classified as birds, not mammals or amphibians.