They also feed occasionally on grain, seeds, freshwater invertebrates, snails and worms. Winter is a sociable time for trumpeter swans, but in late winter the swan families drift apart. The subadult birds form loose flocks, the migrant birds leave for their summer nesting grounds in Canada, and other pairs return to their nearby nesting territories. After spring mating, the pair builds a nest. They may select a new site or refurbish their old one.
Favorite sites are on muskrat houses or in broad beds of marsh plants.
The swans uproot plants in a large ring and build in the center, leaving plenty of open water all around for good visibility. Pairs lay their first eggs when they are 4-6 years of age. Considerable trumpeting and display by both parents usually accompanies the laying of eggs. The pen incubates them for approximately 5 weeks. She covers the eggs with grasses when leaving the nest for several short periods of foraging each day.