In "Caged Bird," what does the line "and his shadow shouts on a nightmare scream" mean?

The
"caged bird" of Angelou's poem is contrasted throughout with its opposite, the
"free bird," who "names the sky his own." The structure of the poem forces
the reader to continually view the differences between the two. Notably, the caged bird never
stops singing, despite its entrapment. He continues to "open his throat to sing" of
something "unknown, but longed-for still"that is, freedom.

In the
fifth stanza, the caged bird "stands on the grave of dreams." This suggests that his
dreams have, for the most part, been buried. But the following line"his shadow shouts on a
nightmare scream"makes us aware that the bird has not actually given up on all his dreams.
The shadow of the bird that once was hopeful is screaming, as if in a "nightmare," at
the thought of losing his dreams and aspirations. It is exactly because "his wings are
clipped and his feet are tied" that the bird is moved to sing, knowing that this is the
only thing he is still empowered to do. The "shadow" of the bird is the part of him
that refuses to concede defeat and sit silent in the cage. Instead, he recalls what he has
"longed for" and sings in support of freedom.