Mute Swans aren’t mute, but their hoarse, muffled trumpet or bugle call given during territorial defense doesn’t carry like the calls of other swan species. Mute Swans also make an explosive snorting or hissing when threatened or disturbed. Mates greet each other with a short, snoring sound, and females solicit their mates with a slow glock, glock call. Female swans call to their broods with a sound like a yapping puppy. When in a group Mute Swans growl, whistle, and snort at each other. Cygnets whistle a soft, low-volume contact call when preening or feeding with adults, and peep noisily at a high pitch when distressed or lost.
As they land Mute Swans slap the water with their feet, either pattering alternately or striking simultaneously, to alert possible intruders. In flight the swan’s wings make a rhythmic humming or whistling sound that carries more than a mile and may help the birds communicate with each other.