Trumpeter swans are the largest birds native to North America. The non-native mute swan is nearly as large, but has a distinctive orange knob on the top of the bill which makes identification easy. Trumpeter swans have a large, stout, black bill. Large male trumpeters can have a wingspan of nearly ten feet. Trumpeters feed mostly on aquatic plants, although in winter they may forage on waste grain and grasses in farm fields.