The caged bird has no freedom. His feet are tied and wings are clipped. He stalks down the narrow cage and can seldom see through the bars of the cage. In this condition, all his dreams seem to be unachievable in his life. He has probably given up on his dreams of liberty and flying freely in the sky. His dreams are now ‘dead’. That is why the poet says that the bird ‘stands on the grave of dreams / his shadow shouts on a nightmare scream‘.
The bird’s movements have been restricted. It can seldom see through the bars of its cage. Its legs are tied and wings are clipped. Singing is the only movement it can do. It doesn’t know what else to do. Its dreams of being free and flying in the sky have been given up by it. This means its dreams are dead and the cage is the grave of its dreams.