Seagull
Swallow
Swift
Starling
A swan is an aquatic bird starting with S and having 4 letters.
Swift
Xenops is a bird. Xantus is a hummingbird.
egret
Flamingo
snipe
American Bittern
· Vulture · Vanga · Vireo
oriole
It could be the Gallinule.
stork
Ibis?