It's never arisen in my limited powered flying career to date, but many years ago I used to glide off Sutton Bank (a prominent ridge soaring site in the UK) and we often shared the airspace with birds. I have read reports of gliders being assaulted, but they've always seemed to be happy to share the space when I've been around. Perhaps there, soaring in a relatively narrow bad of lift at a popular gliding side of several decades' standing has acclimatised the local fauna. I also used to fly radio controlled model gliders at various slope sites, often with hawks in the same block, and one or two people had models attacked (but only if they made moves that the bird might reasonably have considered aggressive).