Male and female Trumpeter Swans give the characteristic deep, trumpeting “oh-OH” call, with the second syllable emphasized. The call is softer and more nasal-sounding when made with the mouth closed. Trumpeter Swans call to keep the pair or family together, to defend territories, or to sound an alarm. Both sexes also use a flat-toned, single-syllable “hoo” call to locate each other. Younger swans make a higher-pitched call, and develop their adult tone by the time they’re 6–8 months old..
Trumpeter Swans slap the water aggressively with their large webbed feet when approaching an intruder. Their wings and feet also slap the water’s surface during takeoff.