A major goal in ecology and evolutionary biology is to understand how environmental change generates a rapid phenotypic response through evolutionary and ecological processes. A particular and currently important form of environmental change is the ongoing global change in climate. There is increasing evidence of micro-evolutionary changes associated with climate and other on selection driven by variation in climate. However, little is known how these are linked and what the underlying physiological adaptations are. A classical way of investigating such adaptation to different environments is the study of genetic colour polymorphism in natural opulations. This is because theory predicts that colour morphs are adaptations to different environments. In this talk I will present long-term data on tawny owl colour polymorphism. I will first show how climate change drives natural selection on colouration and how this translates into micro-evolutionary change. Second, I will present our studies showing the putative mechanisms of this climate-driven selection dealing with plumage insulation, parasite defence and telomere dynamics. Lastly I will present some future prospects of the project.