The passage is a metaphor and foreshadowing (I don’t know if it’s technically foreshadowing if it already happened) of the Marquis’s death and the growing revolution. The “carol of the birds” represents the revolution directly. It is described as “loud and high,” because the revolution is ready to burst, so that burst is being foreshadowed. The bird on the window sill of the Marquis represents Gaspard, who has just killed the Marquis to avenge the death of his own son, and is now looking at the work he has done for the revolution. Gaspard’s “sweetest song with all [his] might” is the fact that he just killed a Noble. As readers, we do not know of any other acts similar done by other peasants, so he stands out from the other peasants in our
