My heart, I cannot still it, Nest that had song-birds in it; And when the last shall go, The dreary days to fill it, Instead of lark or linnet, Shall whirl dead leaves and snow.

The speaker compares his heart to a nest that once held songbirds. When the last bird leaves, the nest will be filled with “dead leaves and snow,” suggesting emptiness and sadness after love departs. The image emphasizes that his love has left, rather than describing a literal physical feeling or his favorite birds.

AI-written and checked against the verified answer.