Oxidative stress is the imbalance between the antioxidant capacity of an organism and the production of free radicals that can damage important biomolecules (lipids, proteins or DNA), affecting cellular senescence. Environmental conditions experienced by organisms can exert a strong influence on the development and expression of their phenotype, especially during early development and reproduction, which may determine access to territories, fecundity and survival. On the other hand, understanding the relationship between oxidative status and telomere dynamics -regions of non-coding DNA whose function is to stabilize the structure of chromosomes and with a fundamental role in ageing- is essential to fully appraise the mechanisms underlying the life-histories determined by the existing trade-offs between reproduction, maintenance and growth. Thus, the main objective of this thesis is to determine, from an ecological-evolutionary point of view, the role of oxidative stress in relation to the different life-histories developed by the birds, analyzing the influence of the nesting environment and the intrinsic and external factors affecting individuals during early development and reproduction. We have studied the physiological adaptations, in relation to oxidative stress, to the different trade-offs that birds face during their life cycle. The Pied Flycatcher (Ficedula hypoleuca) has been used as the study model. The study areas are located in the Sierra de Guadarrama, one in Montes de Valsaín (Segovia), where there are 570 nest boxes, and another one in Lozoya (Madrid), with 100 nest boxes. Both experimental and observational studies have been carried out to analyze the influence of nesting environment and nest-dwelling ectoparasites on nestlings and parental individuals, the costs derived from the reproductive investment and the maintenance of sexual ornaments, the factors affecting the redox status in the early life and the relationships between reproduction, oxidative stress and ageing. Films of nests have been made to analyze parental care and, in all cases, blood samples have been taken from all individuals (adults and nestlings), for analysis of oxidative and biochemical parameters (oxidative damage, antioxidants, triglycerides, uric acid), sex (only in nestlings) and measures of telomeres (adults). In addition, photographs of adult plumage ornaments have been taken to analyze them as a sign of individual quality. This thesis contributes to verify the strong implication of the oxidative state in the trade-offs that sustain life-histories of birds. On the one hand, this thesis shows that the presence of old material in the nest does not affect all populations of ectoparasites equally, questioning the general idea that nest reuse is linked to higher infestations, with consequences on reproductive success and nestling growth. In addition, it is shown how the method to reduce ectoparasite loads of the nest can have uncontrolled effects on birds, which may lead to underestimation of the potential consequences of the presence of such ectoparasites on their avian hosts. We found experimental evidences of negative effects of ectoparasite loads on the oxidative status of adult females and developing chicks, which could have consequences on future survival and reproduction. This study also shows the associations between different components of the oxidative status of developing chicks and various environmental and intrinsic factors, which is essential to understand the importance of oxidative stress in the formation of the phenotype. On the other hand, it is suggested that different achromatic features of plumage can signal the individual capacity to cope with oxidative stress and the importance of the different phases of the reproductive cycle is emphasized to understand the role of oxidative stress as cost and constraint in reproduction. Finally, it is evidenced how the oxidative status is related