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
· Vulture · Vanga · Vireo
American Bittern
It could be the Gallinule.
oriole
stork
Ibis?