Why does the poet use such poetically uncommon bird and tree? What does it reflect?

Why does the poet use such poetically uncommon bird and tree? What does it reflect?

Ans. The poet seems to be in a depressive and sorrowful mood. In such a mood, one cannot think of a sweet and beautiful side of nature. The harsh, bitter and poisonous images come to his mind. That is why he uses an uncommon, harsh, ugly crow and poisonous tree like hemlock.