The poet uses the metaphor of an old eagle to describe the sunset in the poem "An Indian Summer Day on the Prairie".
Step-by-step explanation:
The poet considers the setting of the sun to signify the end of the day. As the poet describes in the poem "The sun is an eagle old; Atop of the spirit-cliffs", the sun is compared to an old eagle on top of a cliff, which is preparing for its death. The last line of the poem "He builds himself a crimson nest" is used to signify the color of the sun and the sky as the sun sets.