• breeding life span
• color polymorphism.
• life history traits
• life reproductive success

Global climate warming is altering the environment of most organisms, leading to changes in selective pressures and animals will need to adapt to these new environmental conditions to persist. Animal with genetically based color polymorphism are ideal study systems in terms of microevolutionary responses to environmental change. In tawny owls, Strix aluco, two melanin-based color morphs exist, brown and grey morphs, associated to different fitness, physiological and behavioral traits. Here we tested if the winter climate before first breeding affected life history components, and if they differ between morphs in six European countries across a latitudinal gradient. Morphs frequency varied greatly across Europe. Brown morph across Europe tend to have a shorter BLS than grey, regardless of temperature before first breeding. LRS differed between morphs in the different populations, with brown individuals having higher LRS in the last 10 years in some countries. Brown individuals breeding after cold winters tended to have lower LRS than grey individuals, whereas after warmer winters they tended to have higher LRS than grey ones. These results suggest that there are differences in fitness between morphs in different populations and that, in tawny owl, harsh climate in early life has differential effects on fitness of the morphs. Thus, at large geographical scale different phenotypes (i.e., color morphs) show different life history strategies according to climate.