Aggression by dominant male bison (Bison bison) toward chemically immobilized conspecifics: a cautionary note

Abstract

The public is occasionally concerned about the detrimental impact of wildlife research activities, particularly capture procedures such as the use of chemical immobilization. One of the risks inherent with chemical immobilization is aggression (or predation) to immobilized animals by conspecifics; yet, data on such occurrences are rarely reported in the literature. We chemically immobilized 25 dominant age-class, large-bodied adult male bison (Bison bison). We observed seven instances (28%) of dominant adult male bison attacking a conspecific that was lying down shortly after being chemically immobilized. Incidences of attacks by aggressive males were more frequent during ground-based versus helicopter-based captures, but this difference was not statistically significant. Contrary to our prediction, we found no difference in the frequency of attacks during mid-summer or late-winter. Our observations highlight the aggressive nature of dominant male bison toward conspecifics and serve as a cautionary note to others chemically immobilizing them. With a marked interest in restoring bison to, and better understanding their ecological role in, their native landscapes, it is anticipated that capturing bison for research and conservation purposes will become more common. We provide suggested best practices so that protocols may be implemented to reduce potential injuries to immobilized bison from conspecifics, and these may also apply to other large, aggressive ungulates.