I was flying the Inspire 1 and it was about 200 ft high in sight if I was watching it instead of my display. While watching my display it suddenly started spinning and fell to the ground. By the time I got to it to recover it some people already was bringing it back to me, They said it was far away but it looked like it ran into a bird. I did not see any birds around it on my screen and one propeller was completely missing. Not broken off but like it came unscrewed. I have crashed drones in the past and broke propellers but never had the propeller hub come completely off the motor screw actually when the propellers hit something they tighten up on the screw and are hard to remove. The thing is I am afraid to fly them if birds are knocking them out of the air or is it more likely that the propeller came off because of my negligence and they just though it looked like it hit a bird. We do have large buzzard in the area but the only bird I seen that wanted to bother with it was small wrens which I wouldn't think could take it down. Edit: From the screen it just looked like it started spinning and I believe something came on the screen about motor speed I never seen before but don't know if it was while it was falling or after it hit the ground.