It may be that Gastornis was an ambush hunter , or used pack hunting techniques to pursue or ambush prey . If Gastornis was a predator , it would have needed some means of hunting prey through the dense forest . Consequently , it has been suspected that Gastornis was an ambush hunter and\/or used pack hunting techniques to pursue or ambush prey ; if Gastornis was a predator , it would have certainly needed some other means of hunting prey through the dense forest .