Bird as bard
Could birds in English literature be a reference to poets and playwrights?
More ancient languages would suggest a different but not opposite meaning.
Birds are often symbolic of the female psyche, and the virtual function of females in the storyworld as potential powerful diplomats. Birds can carry and deliver informed messages (sometimes literally on paper) without causing a direct threat. (Hitchcock's The Birds being one exception) or angelic spy -- a neither necessarily friendly nor necessarily hostile - creature with mobility, a knowledge of other places and times, and the power to interfere in the stories they are spying on. This sounds like a reference to an engaged and imaginative author interacting with his created world. But with the bird metaphor it suggests that the world of the story exists with or without the bird's observation.
Birds interfere in human relationships, intentionally or not, but they do not fully control humans. The mere presence of a bird can be enough to give away, for example, someone's location, or dead bodies, and birds frequently interrupt silence.
Finally, consider that birds are capable of spreading memes with their voices - and they can be trained to behave in a functionally useful way for human ends of gaining knowledge and therefore power.