The way an organism spreads its reproduction over time is defined as a life-history trait,and selection is expected to favour life-history traits associated with the highest fitnessreturn. We use a long-term dataset of 277 life histories to investigate the shape andstrength of selection acting on the age at first reproduction and at last reproduction inthe long-lived Alpine Swift. Both traits were under strong directional selection, but inopposite directions, with selection favouring birds starting their reproductive career earlyand being able to reproduce for longer. There was also evidence for stabilising selectionacting on both traits, suggesting that individuals should nonetheless refrain from repro-ducing in their first 2 years of life (i.e. when inexperienced), and that reproducing after7 years of age had little effect on lifetime fitness, probably due to senescence.Keywords: Apus melba, directional selection, life-history theory, lifetime reproductive success,stabilising selection.How an individual maximises the number of genecopies transmitted to the next generation, namelyits fitness, is key to ecology and evolutionary biol-ogy. The way an organism spreads its reproductionover time is defined as a life-history trait, andselection is expected to favour life-historytraits associated with the highest fitness return(Brommer 2000). In iteroparous species, whichdivide their reproductive investments over severalreproductive attempts, as is the rule in birds, fit-ness generally increases with reproductive lifespan(Clutton-Brock 1988, Newton 1989, Charmantieret al. 2006). Reproductive lifespan is delimited bythe age at first reproduction (AFR) and age at lastreproduction (ALR). Therefore the study of thedegree of direct, indirect and correlational selec-tion acting on AFR and ALR should provideinsight into what life-history trait combinationsmaximise fitness (Lande & Arnold 1983).Despiteitsfundamentalimportance,fitnessisdif-ficulttoestimateinthewild,andinturnselectiononlife histories remains under-investigated (Clutton-BrockS P. Bizeunpubl.data).METHODSData were collected from Alpine Swift populationsin three Swiss cites: Baden, Bienne and Solothurn.The three cities were situated between 21 and85 kilometres apart. In Switzerland, most of the