Dissecting common buzzard lifespan and lifetime reproductive success: the relative importance of food, competition, weather, habitat and individual attributes.

The relative importance of factors such as food, competition, weather, habitat and individual attributes as determinants of fitness in natural populations is difficult to assess. While each component alone can be experimentally manipulated to study its influence on fitness, the relative importance of different factors is very hard to establish experimentally. Here, I describe an attempt to include most major factors simultaneously in an analysis of common buzzard (Buteo buteo) lifespan and lifetime reproductive success (LRS), as two important components of fitness. For both sexes, the most important factor complex determining lifespan and LRS was weather, with high rainfall and cold temperatures reducing fitness. There was no evidence for density-dependent factors influencing buzzard fitness. Habitat variables related to human disturbance were important predictor variables for the dark and light morph but not to the same extend for the intermediate morph. Thus selection pressures resulting from different factors did not vary much between sexes but varied between the three phenotypes in the population.