The poem imagines a changing of the guard in the sky: the hummingbird of day gives way to a hummingbird of night. The night bird is described in glittering, mineral terms, with wings of mica and eyes of yellow quartz. Unlike his daytime cousin, he doesn't fight. Flowers open just for him, and the short summer nights seem to leave no time for battle.
Then the tone turns strange. If you cut him open to find a heart to eat for courage, you'd find nothing beating, only dry husks and moonlight. His powdered wings, the speaker says, are a recipe for madness. The night bird is beautiful, but he is hollow and a little dangerous.
In the final stanza the speaker speaks to "my comrades," as if rallying a group. The call is to give up the daylight world and "feed on dreams." The mood is hushed and dreamy, with a quiet note of defiance. Judging by the title and the imagery, the speaker seems to see night as a place of imagination and a different kind of strength.