What is the author's style in Wild Swans by Edna St. Vincent Millay?

Although "Wild Swans" is only eight lines, Millay introduces a number of literary devices to add depth to the poem. The swans are symbolic of freedom and certainty; that the speaker describes them as wild emphasizes their totally unfettered existence and their instinctual sense of purpose. Millay employs synecdoche (using a part to represent the whole) by referring to the heart.