Migratory birds have during the last decades advanced their phenology, i.e. the timing of events such as migration and breeding, as a response to climate change. Species unable to adjust their phenology have shown declining populations. Understanding the mechanisms underlying this trend is necessary for predicting long term population dynamical consequences of climate change and taking possible conservational action. The proposed project aims at sorting out associations between phenology and changes in population size, and to bridge the gap between these two areas of research classically considered separately. Migratory birds provide an appropriate model system for this purpose due to their apparent phenological responsiveness, well known ecology and the large amounts of data available. More specifically, the aims are approached by i) developing models for quantifying phenological variation and resource mismatch, ii) linking phenology to density dependent population models, and iii) investigating properties of different scenarios by computer simulation. Standardized data from Nordic bird observatories and monitoring schemes will be used in collaboration with responsible institutions. The applicant possesses a unique combination of skills in advanced statistical modelling and natural history, including field experience from bird observatories. The work combines the applicant’s two strongest research topics: population dynamics and bird phenology. The project is carried out at the University of Oslo in an internationally acknowledged research group: Centre for Ecological and Evolutionary Synthesis (CEES), chaired by Prof. Nils Chr. Stenseth. The broad expertise of the CEES and its excellent track record ensures a stimulating environment for carrying out successful research and acquiring complementary skills necessary for career development. The project is likely to provide new insight and stronger tools for assessing climate effects in ecological dynamics.