Goslings, but not adults, show physiological alterations associated with mercury contamination in wild Arctic barnacle geese (Branta leucopsis).

The Arctic is increasingly exposed to anthropogenic contaminants, yet their physiological effects on wildlife remain poorly understood. Mercury (Hg) is of particular concern because it accumulates in polar ecosystems and biomagnifies along food webs. We investigated associations between blood Hg concentrations and multiple physiological markers in wild barnacle geese (Branta leucopsis) breeding in Svalbard. Using blood samples from both adults and their goslings, we quantified Hg concentrations, oxidative damage (lipid peroxidation measured as 4-hydroxynonenal, 4-HNE), metabolomic profiles, and telomere length. Hg concentrations were higher in adults than in goslings. In goslings, but not adults, higher Hg levels were associated with lower 4-HNE, reduced concentrations of several metabolites, and a positive tendency in telomere length, suggesting age-specific physiological responses. These patterns in young may reflect compensatory antioxidant responses at low exposure levels, a coordinated metabolic constraint during rapid growth, and a possible growth-related processes influencing telomere dynamics. These findings suggest that even low Hg environmental exposure may be associated with alterations in physiological pathways during early life stages of wild birds.