I killed a pheasant with my face once, riding my Triumph Bonneville through cornfields here in PA with an open face helmet (back in the days when there were still lots of wild ones around). The blood, guts and eggs came out its ass and went all over my beard and chest, and it almost knocked me out. I got just a scratch on the face, broken glasses, and one 2" piece of the birds intestines got stuck on the rear chrome fender, and sat there a week unnoticed, and the chrome was forever stained with the worm-like impression it made.
I just hit a stocked pheasant and a turkey this year, but both with the same work vehicle. The turkey did quite a bit of damage. Turkey are really plentiful here now, and are a daytime threat.
I also had a close encounter this year riding a fast corner and flying into 5 turkey vultures spread out accross the road around a deer carcass. They took off in that slow motion flight they have, covering the entire two lanes with their bodies just off the ground, and luckily I made it between two of them and the deer. I don't think a buzzard would attack anything, but could maybe make a mistake in flight. They are at the mercy of upward warm-air drafts to keep them aloft. Birds have light, hollow bones, and a collision with anything is usually very costly to them.