Bighorn, Ovis canadensis, males forage together during the non-mating season. As in many other ungulates, vigilance is shared when paired animals face opposite directions. This provides visual coverage over the entire 360 degree circle around the animals.

Even though both animals are feeding, each is able to see animals approaching from their front or side.

Sharing, in this fashion, could be an example of recriprocal altruism, although males may forage with brothers, which would suggest a kin-selection explanation. In either case the cost of sharing vigilance is low and the potential benefits are high.