Telomeres are parts at the end of the chromosomes that protect them from incomplete replication. Telomeres shorten at each cell-division (due to the end-replication problem), and when telomeres become too short, a cell may go into senescence, and is more susceptible to mutations and genetic diseases. Oxidative stress may also result in telomere shortening, resulting in artificial ageing of the cells (and individual), and according to different studies, there is an increase in oxidative stress in wild animal living in urban context, due to chemical pollution, artificial light, and noise, and in fact, animals in urban context, have shorten telomere compare the same in more healthy areas. But although the effects of acute exposure are well documented, the effects of chronic exposure on animal life remain to be explored, and above all, what are the repercussions on the individual of a premature loss of telomere length are still unclear. In fact, telomere length is considered an important biomarker of whole-organism health and aging, because across vertebrates, short telomeres are associated with increased subsequent mortality risk, however still now the processes responsible for this remain unknown. A possible mechanism lies in the fact that telomeres could also be involved in the regulation of gene expression, acting with an epigenetic clock that regulates senescence through a mechanism called Telomere Position Effect (TPE), which can cause different expression in gene at the end of the chromosome by diffusion of heterochromatin. Some genes involved in behaviour could be affected by this phenomenon, validate the selective adoption hypothesis, whereby individuals with shorter telomeres are more likely to adopt specific behaviour patterns, as supported by several observations and the fact that most of the variation in telomere length occurs very early in life, providing little opportunity for adult behaviour to substantially impact telomere length. So, this project has the aim to clarify the possible epigenetic mechanism of gene regulation by telomere length and elucidate the overall effect on fitness and behaviour in wildlife birds.