Dominance hierarchies confer benefits to group members by decreasing the incidences of physical conflict, but may result in certain lower ranked individuals consistently missing out on access to resources. Here, we report a linear dominance hierarchy remaining stable over time in a closed population of birds. We show that this stability can be disrupted, however, by the artificial mass loading of birds that typically comprise the bottom 50% of the hierarchy. Mass loading causes these low-ranked birds to immediately become more aggressive and rise-up the dominance hierarchy; however, this effect was only evident in males and was absent in females. Removal of the artificial mass causes the hierarchy to return to its previous structure. This interruption of a stable hierarchy implies a strong direct link between body mass and social behaviour and suggests that an individual's personality can be altered by the artificial manipulation of body mass.

支配等级通过减少身体冲突的发生率来为团体成员带来好处，但可能导致某些排名较低的个人始终错失获得资源的机会。在这里，我们报告了在封闭的鸟类种群中随时间保持稳定的线性优势等级。然而，我们表明这种稳定性可能会被鸟类的人工质量负载破坏，这些鸟类通常构成层次结构的底部 50%。大量加载会导致这些低等级的鸟类立即变得更具攻击性并提升优势等级；然而，这种效果只在男性中明显，而在女性中不存在。去除人工质量会导致层次结构返回到其先前的结构。