It's on the whole a factual poem about the way things look and behave in the world of trees and fields.

Crow's Nests

That lofty stand of trees beyond the field,
Which in the storms of summer stood revealed
As a great fleet of galleons bound our way
Across a moiled expanse of tossing hay,
Full-rigged and swift, and to the topmost sail
Taking their fill and pleasure of the gale,
Now, in this leafless time, are ships no more,
Though it would not be hard to take them for
A roadstead full of naked mast and spar
In which we see now where the crow's nests are.

Now that's just a simple fact. That's where crow's nests are, in the tops of trees, though not everybody knows it.

[Q] But you have to know about crow's nests, then.

Yes.

[Q] On ships.

On ships as well.