Some birds, such as warblers and birds of prey, migrate alone, but birds such as starlings, pigeons and godwits move in vast flocks.
(Some birds, such as warblers and birds of prey; migrate alone; ) (birds such as starlings, pigeons and godwits; move; in vast flocks)
Some birds, such as warblers and birds of prey birds such as starlings, pigeons and godwits
migrate alone move
in vast flocks