The title, The Scarlet Ibis, is rather mysterious. It doesn't prepare us for what the story will be about. If we know that a scarlet ibis is a bird, we might have a picture of that in our heads. In any case, unless we've already heard something about the story, we enter with a sense of mystery. As we discuss in "Writing Style" the ibis "frames" the story. In addition to making up the title, it's mentioned in the first and last sentences.
In spite of this, it's obvious that "The Scarlet Ibis" is more about Brother's guilt over Doodle's death than about the ibis itself. Brother uses the death of the ibis as a way to cope with the death of his brother, to deal with the guilt he feels for causing it. So how exactly does this work? Are Doodle and the ibis actually similar? Let's investigate that question.
The scarlet ibis isn't native to North Carolina. As Daddy says after consulting the bird book, "It lives in the tropics – South America to Florida. A storm must have brought it here" (4.29). But, the fact that the ibis is away from its natural home is not what causes its death. It dies because it is injured in a storm. But, there is still a sense that the ibis doesn't belong in North Carolina, that it is different from other birds in North Carolina.
Doodle, unlike the ibis, was born in North Carolina. Unlike the ibis, Doodle would be different no matter where he was born. His physical disabilities make him different from most other kids. Part of this is because Doodle's heart condition isn't understood by the doctor or by his family. It's unlikely that it will be understood by most of the kids Doodle would have met if he'd gone to school.
Unlike the ibis, Doodle doesn't die because he's been in a storm. He overexerts himself rowing, then overexerts himself more by running, and then gets frightened when Brother abandons him in the storm. He is in a storm, but he most likely dies as a result of his heart condition.
In any case, both bird and boy are in storms that contribute to their deaths. Both boy and bird die away from their families. Ironically, the ibis dies surrounded by Doodle's family, but Doodle dies completely alone – his family is nowhere to be seen.
Brother knows the ibis dies because it was caught up in the forces of nature. It's unlikely that a person had anything to do it. Brother also knows that this is unlike what happened to Doodle. He knows that he put Doodle in the storm, pushed him beyond his endurance level, and then abandoned him. Doodle's death was preventable. That's pretty heavy stuff for a thirteen-year-old to deal with.
When brother sees that Doodle's body is limp, like the ibis's body in death, and that the blood has painted Doodle's neck red, he finds boy and bird physically similar. He says that he was protecting his "fallen scarlet ibis" (5.51). By connecting Doodle with the ibis, who "even in death" retains its "exotic beauty," Brother can at least pretend that Doodle's death is natural, unavoidable, and even beautiful (4.25). This would sound like a cop-out, but even a quick reading of the text shows that Brother blames himself a little too much for what happened. He needs something, anything, to blunt the guilt that's attacking him. The ibis is what he chooses.
Connecting Doodle with the ibis is also a way to honor Doodle's memory. Doodle is so disturbed by the death of the ibis that he loses his appetite. By burying the ibis, Doodle tries to honor its life. The ritual of burial is his demonstration of reverence for life. As you can see, the ibis isn't a mere "symbol" of Doodle. In fact, there are very few similarities between bird and boy. Rather, the ibis is a way for Brother to cope with the pain and guilt. It's also a way for him to honor Doodle by comparing him to something that Doodle honored.