Researchers at RMIT University in Melbourne, Australia have made a groundbreaking discovery about how kestrels stay perfectly still while hovering. By training two nankeen kestrels to fly inside a wind tunnel and filming their movements with 52 reflective markers, scientists were able to create 3D models and study the birds' behavior in detail. The findings show that kestrels achieve stillness by deftly moving their wrists and subtly extending and retracting their elbows, while also using their tails for extra stability.

Source: https://www.newscientist.com/article/2443209-we-now-know-how-kestrels-stay-perfectly-still-while-hovering/