In seasonal environments populations of short lived animals can experience a reproductive season with multivoltine reproduction and a non-reproductive season. This pattern produces a bimodal distribution of distinct individual life histories (short-lived summer and long-lived winter animals) within genetic lineages. We hypothesize, that for distinct life history patterns also different behavioural syndromes are fitness increasing: summer animals should be bold, competitive, and aggressive to overcome competition with conspecifics, while winter animals should be shy, social and careful to save energy and avoid predation. Here we investigate, whether different behavioural syndromes are selected during summer and winter, or, alternatively, behavioural symptoms plasic, and is photoperiod triggering the fitness-enhancing behavioural syndromes in small mammals? We will investigate these questions on different ecological scales. In wild populations we will monitor the frequency of bold and shy animals along cohorts to detect potential selection on behavioural syndromes. In large outdoor enclosures we follow the fitness of bold and shy animals over different seasons. In the laboratory we will try to trigger behavioural syndromes by manipulating the change in day lenght during ontogeny. With this comprehensive approach it may be possible to understand the maintenance of variability in behavioural symptoms in nature.