What is the irony in "The Scarlet Ibis"?

There are several key examples of irony in James Hurst's "The Scarlet Ibis." Doodle's real name, William Armstrong, is a glaring one: A long name that suggests physical strength, it does not fit the weak and sickly younger brother. The weary scarlet ibis that tumbles from the bleeding tree and dies in the yard is another. Doodle, who had recently shocked his parents by standing up and walking across the room without assistance, quickly identifies with the colorful creature that now lies before him. A lone bird, it was out of place in this world, and he buries the beautiful, red, dead creature. Doodle's triumphs of the previous months seemed unimportant to him now. Just hours later, he, too, would die alone, limp and blood stained. It was now the older brother's turn to shelter his fallen scarlet ibis.