bison bulls, dominance, age, weight, Behavioral Science & Comparative Psychology, 0608 Zoology, 0702 Animal Production, 0707 Veterinary Sciences
In the wild, male American bison (Bison bison) aggregate only during the breeding season or rut with female herds to reproduce. During the non-rut, they form bachelor groups. Very little is known about dominance structures in these bachelor herds. In this report, we evaluate social dominance in bachelor groups of bison bulls kept on a commercial bison farm in Belgium, where natural seasonal grouping dynamics are imitated. Observations were carried out during five different non-rut periods over several years. Agonistic behaviour was scored and used to determine dominance rank. The relationships between dominance and the individual factors age and weight were evaluated. We found a strong and significantly linear dominance hierarchy in the male bachelor groups. There was a reversal in rank among same-aged individuals between two subsequent study periods during one non-rut period. Dominance and age were strongly correlated in every study period, as were dominance and weight. We conclude that during non-rut bison bulls can form temporary groups with a linear dominance hierarchy in which older and heavier individuals occupy the highest social positions. © 2004 Elsevier B.V. All rights reserved.