**Individual variation in reproductive success of willow ptarmigan in relation to climate** Climate change induced changes in individual life histories may lead to perturbations in the population dynamics. Thus, there is a need for research to understand the ecological connections between climate, variation in life history traits and demography. Because resources acquired by individuals are limited, climate conditions migth also interfere with individual’s energy budget and influence the allocation of resources to growth, self-maintenance or reproduction. Accordingly, trade-offs between life history traits such as survival rates, reproductive rates and growth are predicted to have direct effects on population dynamics. In addition to external factors like weather conditions, trade-offs between investment to own survival and recruitment might vary between individuals depending on their age and body condition and previous trade-off decisions. Many bird species are plastic in terms of clutch sizes, which might vary in relation to the climate driven resource situation. Further, the state of individuals (e.g. age, body condition) can affect both the amount of resources available and/or allocation of resources in terms of number of offspring. In such cases, it is predicted that there is a relationship between individual state variables and litter size. However, other studies suggest that an optimal clutch size (or litter size in mammals) can be independent of individual state if environmental conditions are unpredictable. We will apply a unique 17-year historical time series of individual based life-history data on willow ptarmigan (Lagopus lagopus) to address relevant hypotheses related to the influence of climatic factors on individual variation in reproductive success. The hypotheses and analysis plans are outlined in the attached files.