I think that the poem sheds much light on various human traits. One such trait is the need for control and power. The frog represents this trait with his manner and demeanor towards the nightingale. The frog recognizes that his status in the bog is scrutinized with the song of the nightingale. He cannot compete with her talent, and yet does not want to relinquish his role as the chief vocalist of the bog. His plan to ensure that her voice is trashed through his "rigor" is reflective of the human trait of control. The ending of the poem in which the nightingale has been eliminated and he remains in control is reflective of a sadly human trait to want to appropriate the world in accordance to our own subjectivity.
For the nightingale, the human trait of naivete is evident. The nightingale is naive. She possesses talent and has a gift of song. The other animals love her singing and she sincerely believes that the frog can be a mentor for her. While the frog might reflect the human desire to control, it becomes easy for him to accomplish this end with the nightingale being such a willing subject. She never engages in reflection or scrutiny as to the frog's motives. Her human trait of being naive is reflective in how easily she succumbs to what he asks of her. She gives her all, sadly and with blind faith, until she literally has nothing left to give. It is here in which she embodies the human trait of being naive.