Within each bonus mission are four challenges (except the Hoole bonus mission - no bombing challenge). You must complete all the challenges in each bonus mission, to unlock this achievement. I recommend using the Barn Owl or the Spotted Owl. The challenges are:
Bombing
- Destroy all the turrents, and ignore all enemies except for countering. Best Battleset: Diamond Dash
Owlet Rescue
- Similar to the "Thieves in the Night" story mission, you must rescue owlets and return them within a certain amount of time. Best Battleset: Diamond Dash
Survival
- You must fight off five (5) waves of enemies in a certain amount of time. The game does make it a bit easy, by stopping the timer inbetween waves. Since this is a fight challenge, use your combos. Best Battleset: Burning Spirit/Iron Fortitude
Speed Flying
- Similar to the "Race to the Retreat" story mission, you must fly a course through rings in a certain amount of time. This one can be annoying, and the Tyto one is the hardest I found. If you miss three rings you will be starting over, except for the Beaks challenge where you get fives rings to miss. Best Battleset: Diamond Dash
Btw.... If you leave negative feedback, please explain why so I can adjust. Thanks.