Technically you can although in the uk swans are protected by the crown, in the us there is no such law more likely then not you will never come across a person who has eaten or much less killed a swan
Swans feed almost entirely on underwater vegetation. However, in winter they sometimes also eat grass or grains.
Whooper swans eat people small baby cows snakes and butterfly
No, swans and ducks are both plant eaters.
No.
Loons (US), or Divers (UK) eat mainly fish, with amphibians, crustaceans, and aquatic insects supplementing their diet.
yes
Yes
yes
No
Insects
yes
it eats small insects