This is a logic puzzle. Assume one is telling the truth. If Hawk is truthful, then Sparrow is lying (Hawk said Sparrow is lying). If Sparrow lies, then Hawk did not steal it. The Owl's statement "Hawk said the owl stole it" makes no sense with the given facts. Let's re-read. If we assume only one bird is lying. If the Hawk lies, then the Sparrow tells the truth ("Hawk did it"). This works. If the Owl lies, then the Hawk didn't say the owl did it. If the Sparrow lies, then the Hawk didn't do it. The question is ambiguous. [The source provides Eagle as the answer without explanation].