1. Identifying which factors influence age and size at maturity is crucial for a better understanding of the evolution of life-history strategies. In particular, populations intensively harvested, hunted or fished by humans often respond by displaying earlier age and decreased size at first reproduction.
2. Among ungulates wild boar (Sus scrofa scrofa L.) exhibit uncommon life-history traits, such as high fertility and early reproduction, which might increase the demographic impact of varying age at first reproduction. We analysed variation in female reproductive output from a 22-year long study of an intensively hunted population. We assessed how the breeding probability and the onset of oestrus responded to changes of female body mass at different ages under varying conditions of climate and food availability.
3. Wild boar females had to reach a threshold body mass (27–33 kg) before breeding for the first time. This threshold mass was relatively low (33–41% of adult body mass) compared to that reported in most other ungulates (about 80%).
4. Proportions of females breeding peaked when rainfall and temperature were low in spring and high in summer. Climatic conditions might act through the nutritional condition of females. The onset of oestrus varied a lot in relation to resources available at both current and previous years. Between none and up to 90% of females were in oestrus in November depending on the year.
5. Past and current resources accounted for equivalent amount of observed variations in proportions of females breeding. Thus, wild boar rank at an intermediate position along the capital–income continuum rather than close to the capital end where similar-sized ungulates rank.
6. Juvenile females made a major contribution to the yearly reproductive output. Comparisons among wild boar populations facing contrasted hunting pressures indicate that a high demographic contribution of juveniles is a likely consequence of a high hunting pressure rather than a species-specific life-history pattern characterizing wild boar.