In “The Scarlet Ibis,” Doodle is best symbolized by the bird, the scarlet ibis, because

both are rare and unusual creatures who are tragically separated from their families.
both are fragile creatures who struggle in their environments before dying tragic deaths.
Doodle loved rare and unusual birds that he felt were similar to him in a variety of ways.
Doodle saved the fragile bird, much as his brother attempted to save him when he was young.