Behaviour is often both repeatable among individuals (i.e. personality) and plastically adjusted within individuals according to environmental conditions or age. Yet, little is known about the repeatability and age-related plasticity in behavioural traits across the lifetime of free-living animals, which is, however, crucial for understanding the development and evolutionary consequences of personality in the wild. Here, we explored long-term (co)variation and age-dependent expression of two female behaviours, female–female aggression and hissing behaviour, using longitudinal data of free-living great tits, Parus major. Both behaviours were repeatable across years but did not covary among females into a behavioural syndrome. In contrast to hissing behaviour, female aggression declined with age on the population level, which was due to within-individual plasticity in aggression and not selective disappearance. Moreover, individual females differed in their level of plasticity, with more aggressive females showing a steeper decline in aggression than less aggressive females, resulting in a pattern where females became more similar in aggression with age. At the same time, the repeatability of aggression increased with age, mostly driven by a decrease in within-individual variance across age. Large between- and within-individual differences in same-sex aggression in early life and a higher repeatability in later life may be functionally linked to age-dependent requirements and constraints. Overall, our findings suggest that how female aggression will respond to selection might depend on when during the life cycle selection is operating, which has important consequences for the understanding of the evolutionary dynamics of animal personality in the wild.

行为通常在个人（即人格）之间是可重复的，也可以根据环境条件或年龄在个人内进行可塑性调整。然而，关于自由生活动物一生中行为特征的可重复性和与年龄相关的可塑性知之甚少，然而，这对于理解野外人格的发展和进化后果至关重要。在这里，我们使用大山雀（Parus major）的自由活动大山雀的纵向数据，探索了两种女性行为（女性对女性的攻击和嘶嘶行为）的长期（共）变异和年龄依赖性表达。两种行为在数年内都是可重复的，但并未在女性之间转变为行为综合症。与嘶嘶行为相反，女性的侵略性随着人口年龄的增长而下降，这是由于侵略性在个体内部可塑性而非选择性失踪所致。此外，个体雌性的可塑性水平也不同，攻击性强的雌性比攻击性弱的雌性显示出更陡峭的下降，导致女性的攻击性随着年龄的增长而更加相似。同时，侵略性的可重复性随着年龄的增长而增加，这主要是由于年龄范围内个体内部差异的减少所致。早期同性攻击的个体之间和个体内部差异较大，而后辈的重复性较高，这在功能上可能与年龄相关的要求和约束联系在一起。总体而言，我们的研究结果表明，女性攻击对选择的反应方式可能取决于生命周期中选择的时间，这对于了解野生动物个性的进化动力学具有重要意义。