Sparring, relative antler size, and assessment in male caribou

Summary

There are two kinds of antler combats in male deer. Fighting is rare, violent, occurs between matched males, and can cause injury and death. Sparring is common, usually gentle, often occurs between unmatched males, and involves no risk of injury. We recorded 1308 sparring matches and only 6 fights between wild male woodland caribou (Rangifer tarandus caribou) in 2 years of study. In the 713 sparring matches between males with unequal antlers, the animal with smaller antlers initiated close to half of the encounters, but terminated nearly 90% of them. That was true whether a sparring match involved two adults, two yearlings, or an adult against a yearling. We argue that the best interpretation of that shift in the decisions of the smaller-antlered male is that sparring serves to assess a partner's weight and strength relative to one's own. Thus, through sparring, antlers could be used to allow a form of tactile (proprioceptive) assessment of fighting ability, which could be the basis for subsequent visual assessment at a distance.