Don't Predators hunt Aliens for trophies?  In the 2nd Predator movie, there
was an Alien skull in the Predator's trophy display. 

Yes, predator's hunt Aliens. 
Predator's PUT the xenomorphs on worlds, just to have a new place to 
"hunt." Seen the predator v. aliens arcade game? The game is a direct 
result of the hunters putting their prey on earth.

	Thomas Hamill