Corticosterone mediates telomere length in raptor chicks exposed to chemical mixture.

•Lead and mercury concentrations in Red kite were below the toxicity thresholds for wildlife.•Corticosterone increased with Hg and Pb in interaction showing an effect on this hormone.•Telomere length (TL) was not linked to metal while it was related negatively to corticosterone.•Results support that TL could be an indirect consequence of metal mediated by corticosterone.