Really this entire concept is stupid. Not only are higher-end quadcopters unimaginably acrobatic, to the point where a skilled pilot could easily outfly a bird, but these things are literally flying lawnmowers. Go on /r/Multicopter or any other multirotor forum, there are loads of people that have been sliced all over their arms, and if you dig further, cuts down to the bone in some cases. Given the brittle, hollow nature of bird bones, well. (maybe eagle/falcon legs are different tho?) Seriously, if I was a falconer I would never consent to this. As for people suggesting they use cords or something to tangle the props up, that's really not an impossible problem either, people have been putting mesh cages over their props to fly them safely indoors for some time now, plus if you only stop one prop the quad becomes extremely violent in it's movements, pitching and rolling all over the damn place, which again, will probably at the very least hurt the bird quite a lot. Plus, if you were using quads for nefarious purposes, if that bird catches your quad you're not gonna give up and call it a day, more likely you'll push the throttle to max, which again, will cause that bird quite a lot of harm. If I were the aforementioned falconer, I would make sure the pilot cut the motors immediately before the eagle caught it, as that's the only way this would ever be safe for anyone involved.