What are the symbolic connections between the ibis and Doodle?

In "The Scarlet Ibis," there are a number of symbolic connections between the ibis and Doodle. Firstly, in the opening lines of the story, Brother remembers seeing an ibis come to a tree, and it is that memory which triggers the memory of Doodle. For Brother, the arrival of this bird is linked to the arrival of his little brother.
Secondly, the ibis is an unusual, tropical bird which stands out from others, and Doodle has a similar quality. His physical weakness and fragility, for example, make him different from other boys. Note, at the end of the story, how Brother refers to Doodle as my "fallen scarlet ibis." Through this phrase, Brother is alluding to this unique quality about his brother and his strong desire to protect him, just as you would protect a special, endangered bird.
Finally, toward the end of the story, the scarlet ibis dies and Brother insists on burying the bird. The death of the ibis not only foreshadows Doodle's death, it makes an important point about beauty. Namely, we cannot always protect the beautiful and the fragile. This idea applies directly to Doodle; Brother, no matter how hard he tries, cannot save him from death.