In recent years ecological research has focused on the relevance of antioxidants and oxidative stress in the evolution of life-history strategies and physiological trade-off in birds. Some studies sought to evaluate whether a consequence of immune response is oxidative stress. In a meta-analysis of 16 studies of ten species of birds including 49 estimates of effect size from experimental studies, we show that induction of an immune response in a diverse group of bird species may determine oxidative stress (variance explained: 4.1%), but, most notably, may determine changes in oxidative stress markers (variance explained: 15.0%). These conclusions were robust to control for sampling effort and publication bias. Finally, this finding suggests that (1) oxidative stress may be a physiological cost associated with the immune response and (2) an important role of antioxidants in birds is to control the potentially negative effects of such oxidative stress to prevent immuno-pathological damage to host tissues.