In a global change scenario, emerging infectious diseases are becoming more frequent and harder to prevent or control. In birds, malaria parasites are responsible for wildlife population declines of many species worldwide. Despite being exposed to the same risk, there is a clear inter-individual variation in the susceptibility to malaria. As hormone-mediated maternal effects may act as mechanisms of phenotypic plasticity facilitating the offspring's adaptation to new environments, here, we explored the dose-dependent response to maternal yolk hormones by experimentally injecting two different testosterone (T) doses into the egg yolks of wild great tits. High prenatal T levels could carry short-term benefits (i.e. accelerated metabolism and growth) but carry long-term costs including accelerated telomere shortening (i.e. a hallmark of ageing) and depressed immunity that could both increase susceptibility to malaria. Our preliminary results show no effects of T-treatment on body size or condition of nestlings, but chicks treated with the higher T-dose had higher breathing rates. Nestling survival to fledging was positively influenced by prenatal T (higher T-dose > control and lower T-dose), while we found no evidence of an effect on hatching success or post-fledging survival. The medium to long-term costs of prenatal T are currently investigated through post-natal telomere dynamics and malaria susceptibility measurements at the post-fledging stage, with the prediction that the short-term benefit of prenatal T should lead to shorter telomeres and accentuated malaria susceptibility. Future studies should carefully consider a range of concentrations, as the balance of costs and benefits of prenatal hormones may be dose-dependent.