Short, sweet, and timely, with a target audience just prior or during the initial developmental need for the moral of the story. This is a book about dreams failing regardless of hard work, and not just carrying on but finding value in something else entirely. This involves acceptance that you're not good at everything, and how pursuing what you're good at can be more useful than perseverance on something you're not. Children inevitably discover how their skills and abilities stack up against other children during school, and this lesson is very important, if secondary to perseverance itself. The bird's specialization takes him far beyond the bird community, where it would be less useful. His skills and where they're socially valued imply a more global sort of "economy," with more specialization in individual roles and reliance on others for other aspects of life, like flying. A lesson needed more in modern life than at other times, historically. I'd say grades P-2 makes sense, though the story covering the lesson might get too simple for kids K-2.