grebe
A swan is an aquatic bird starting with S and having 4 letters.
puffin, or just a bird is a parrot.
A six letter word for a bird of prey starting with the letter R is "raptor."
Goose
crane
Gull.
grebe
loon
It could be a Plover.
Teal
Ibis?
A possible word is pelican, a large aquatic bird.