Is the personality of Tree Sparrows (Passer montanus) in heavy metal-polluted environments undergoing silent change?

Environmental heavy metal pollution is a major survival pressure for wild birds, often causing behavioral changes. However, the mechanisms shaping avian personality traits in heavy metal-polluted environments remain unclear. This study focused on the tree sparrow ( Passer montanus ), selecting Mantoushan Village in Jiaozuo City as the polluted site and Geliaofan Village, 17 km away, as the control site. Combining field sampling with laboratory analysis, this study measured the accumulation of heavy metals (Zn, Cr, Cu, Cd, and Pb) and Ca in tree sparrow tissues, evaluated morphological developmental instability [fluctuating asymmetry (FA)], and quantified four sparrow personality traits: exploration, boldness, activity, and sociability. Results showed that concentrations of Cu, Pb, Cd, and Cr in multiple tissues, as well as FA levels, were significantly higher in sparrows from the polluted site than the unpolluted site. Additionally, adults and juvenile males from the polluted site exhibited significantly higher activity and sociability scores, whereas sparrows from the unpolluted site had higher heart rates and longer maximum stationary times. Furthermore, Cr, Cd, and Pb exerted significant negative effects on sparrow FA levels. Correlation analysis revealed that Cu, Pb, Cd, and Cr accumulation, as well as FA levels, was associated with boldness, activity, and exploration scores in sparrows, indicating that heavy metals may be key factors inhibiting behavioral performance. These findings provide evidence for understanding the personality traits and individual state responses of wild birds under heavy metal pollution. • Cu, Pb, Cd, and Cr levels were significantly higher in sparrows from a polluted site. • FA levels were higher in polluted-site sparrows, especially juveniles. • Sparrows from the polluted site showed greater activity and sociability. • Metal concentrations were significantly negatively correlated with personality levels.