Veteran Spanish actor Simón Andreu is credited with the role of "Barman" in the cast listing during the credits of all three of the English-language versions, but his performance not actually present in any of those prints in the versions which have turned up on home video.
The interior scenes inside of the hunting lodge were all filmed on a soundstage at Pinewood Studios in England on a life-sized set. The opening scenes at Kenny's house and the exterior scenes on the island were all filmed on location in Spain. Additional "highway" scenes were probably filmed in Northern Michigan by a 2nd unit crew.
The screenplay was adapted by author David D. Osborn from his own novel of the same name. The movie credits refer to a work called "The All-Americans" but in actuality the book was simply called "Open Season" (Dial Press, New York, 1974).
When Ken and Artie climb the bluff, Ken is carrying a bolt action rifle. But after they split up and Ken returns to the lodge, he enters the cabin carrying a pump action shotgun. The rifle is never seen again.