In the novel of Being Henry David by Cal Armistead, what is the significance of the black bird? A figure of black bird comes up in chapter 4, and it is also the name of the song that Hank remembers from the Beetles. Are there any correlations between the two? What's the significance of it? Is this an example of a symbol? In a bigger picture, does this represent an element of American Romanticism/Gothics/Transcendentalism? How?

In the YA novel Being Henry David, a teen wakes up in New York City’s Penn Station without any clue of who he is and how he got there. Since all he has is a copy of Thoreau’s Walden, he calls himself “Hank.” And he uses some select inspiration from Henry David Thoreau to find his answers.
I am fortunate enough to have social media connections to author Cal Armistead, so I posed your query directly to her. She was surprised and honored to be asked such intricate questions about her book, which was published in 2013. She quickly replied, “The blackbird in Hank’s dream is a symbol of Magpie, the bad guy in NYC.”
It took her a bit longer to think about a connection between the appearance of the dream bird and the lyrics to the Beatles’ song “Blackbird.” After all, Ms. Armistead wrote this manuscript more than five years ago. As a writer myself, I can attest to the fact that some symbols and connections can be deliberately included by the author, and others can just materialize on the page as if by magic. We readers don’t know which is which. It’s possible she didn’t even formally consider the relationship at the time of the writing. After some thought, however, she said: “The blackbird is Hank's unconscious and the memories that are shrouded by amnesia. This knowledge can harm him, but it will also set him free. (As in “Blackbird, fly . . .”).”
If you listen to the song (through the link below), you may come to better understanding of the connection. You could see Hank in the blackbird. He could certainly be said to have “broken wings” and “sunken eyes” at the beginning of the story, and he needs to learn to fly and to see again. He’s reached a point in his life where he is “only waiting for this moment to be free.” Does he find this freedom? How?
It’s up to us to further compare this relationship to the characteristics of the literary movements you suggest. For example: Using natural elements to explain social behavior. Valuing individual freedom. Valuing intuition and imagination over reason and reality. Finding God in nature. The author may not have intentionally set out to make this book an example of American romanticism, but by using Thoreau as a centerpiece and by focusing on a main character in need, she certainly leads us to think in this direction.