I assume your question refers to the foreshadowing that exists in this excellent short story that indicates the end of the tale. Foreshadowing can be defined as the way in which the author plants or places careful clues or hints about what is going to happen later on in the tale and by so doing increases the suspense. If we examine the beginning of the tale there are plenty of indications about what is going to happen to Doodle and his fate. Note the way that Doodle's father had a coffin built for him and also the comment that the narrator makes about the naming of Doodle:
They named him William Armstrong, which was like tying a big tail on a small kite. Such a name sounds good only on a tombstone.
Both of these examples of foreshadowing thus in a sense point towards the early death of Doodle at the end of the novel, and this sense is strengthened by the appearance of the scarlet ibis, that Doodle feels a strange kinship with, and that the narrator uses to compare his brother with. Both Doodle and the scarlet ibis are rare and exotic creatures who clearly don't belong where they are.