The tone the author used is sad and sorrowful. Doodle's father had a coffin built for him. Also, the brother was sad and disappointed that he might have a brother that was not "all there".
Style
Graveyard flowers, going to die, and the last paragraph using "I began to weep" and "tear-blurred" to demonstrate sorrow.
Theme
"It was in the clove of seasons, summer was dead ..." and "summer had long since fled..."
The author uses a descriptive style in describing the oriole nest as rocking like an empty cradle and describing the ibis as a broken vase of red flowers.
The older brother tells the story in the past tense of the sadness of losing his little brother at a young age. He compares his little brother to the lost and dying scarlet ibis.