Most people, when picturing swans, think of the orange-billed ones: Mute Swans, which are an invasive species. 

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.
 
Get a romantic swan greeting card here! They're 5-1/2" square on premium 16-pt cardstock.