Date of Award:
Doctor of Philosophy (PhD)
Frederick D. Provenza
Frederick D. Provenza
Johan du Toit
Social organization varies widely among herbivores, and the level of social organization in bison is widely debated. I hypothesized that when mother-daughter relationships are allowed to develop, bison form long-term associations. In my study, 25 treatment mothers were selected from a free-ranging herd and kept together with their calves, while 25 control females had their calves forcefully removed. Treatment mothers and offspring had by far the greatest number of associations with a greater percentage of individuals with a half weight index (HWI) > 0.50. The strongest associations (HWI > 0.31) were among treatment mothers and their offspring. Moreover, these associations persisted over multiple generations. Group coordination requires group decisions and these can vary between extremes. I hypothesized bison utilized both democratic and despotic decisions. I examined movement initiation and direction decisions following rest periods. For direction decisions older cows repeatedly made decisions despotically for the group; in 93% of the choices, group directions were within 95% confidence intervals. For movement initiation, bison used a more democratic decision-making process; group movements did not begin until an average of 47% of adult cows exited the group. Interestingly, the oldest females led this final post-rest movement behavior in 81% of the decisions. Presumably, living in properly functioning social groups has many benefits, including reduced stress. I hypothesized levels of stress was related to animal density. Consequently, yearling bison males were weaned and placed in either 1) tight confinement (TC), 2) loose (LC) confinement, or 3) free-ranging (FR, returned to herd). I measured fecal cortisol metabolites (FCM) as an index of stress. Fecal samples were collected in each group every 2 weeks from January to April 2009. Fecal cortisol levels were lowest for FR (23 ng/g DM), intermediate for LC (39 ng/g DM), and highest for TC (63 ng/g DM; P
Shaw, Ryan A., "Social Organization and Decision Making In North American Bison: Implications For Management" (2012). All Graduate Theses and Dissertations. 1204.
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