• behavioural syndromes;
  • coping style;
  • lifetime reproductive success;
  • pace of life;
  • state-dependency


  1. Understanding the causes of animal personality (i.e. consistent behavioural differences) is a major aim of evolutionary studies.
  2. Recent theoretical work suggests that major personality traits may contribute to evolutionary trade-offs. However, such associations have only been investigated in a few study systems, and even less so in free ranging animal populations.
  3. Eastern chipmunks exhibit consistent individual differences in exploration, ranging from slow to fast. Birth cohorts also experience dramatic differences in age at first breeding opportunity due to annual differences in beech mast. Individuals may breed for the first time at 24, 33 or 50% of their average life span, depending on year of birth. Here, we used data from a long-term survey on a wild population to investigate the relationship between reproductive life history and consistent individual differences in exploration. We determined whether predictable differences in age at first breeding opportunity among birth cohorts were associated with exploration differences and favoured individuals with different exploration.
  4. Birth cohorts with a predictably earlier age at first breeding opportunity were faster explorers on average. Slower explorers displayed their highest fecundity (females) or highest fertilization success (males) later in their life compared with faster explorers. Overall, slow explorers attained a higher lifetime reproductive success than fast explorers when given an opportunity to reproduce later in their life.
  5. Our results suggest that the timing of mating seasons, associated with fluctuating food abundance, may favour individual variation in exploration and maintain population variation through its effects on reproductive life history. Together, our result shed light on how fluctuation in ecological conditions may maintain personality differences and on the nature of the relationships between animal personality and life history.