The ibis symbolizes Doodle, and he recognizes this connection when the bird falls out of the tree. Doodle's parents want him to leave the bird alone, but Doodle--seeing the similarities between the fragile bird and himself--will not let it be. He buries the bird, and the self-sacrificing act drains his strength.
Other similarities between Doodle and the bird are that they both have a scarlet exterior and seem out of place in their environments. In fact, the arrival of an ibis at the beginning of the story causes Brother to flash back to his boyhood with Doodle. Likewise, when Brother finds Doodle dead in the rain, his form reminds the narrator of the fallen scarlet ibis. Neither Doodle nor the bird is expected to survive, but both leave indelible impressions on those who come in contact with them.