Possible Clues:

• Nestling they assume is hiding -
• Bird, I agree, will return at start of spring
• Young hawk in European state making a comeback
• Observed in spinney - a sprightly young hawk
• Hawk always returns South
• Nestling bird in spinney, a sparrowhawk
• Young bird of prey ascending
• The old get around like a young hawk
• Young falcon
• Trained in falconry? That's a yes!