Behavioral assessment of heavy metal pollution effects on birds unveils species-specific responses to different elements

Heavy metal pollution can alter animal behaviors in ways that can significantly reduce fitness. However, the direct influence of exposure to highly polluted environments on behavioral traits has rarely been studied in the field. Here, we investigated the effects on behavior of heavy metal accumulation by analyzing four primary heavy metals—Mercury (Hg), Copper (Cu), Zinc (Zn), and Cadmium (Cd)—extracted from feathers of six passerine bird species from a heavily polluted subtropical region in southwest China. We examined the correlations between these heavy metals’ concentrations and three behavioral traits assessed during handling: breath rate, distress calls, and handling aggression. We recorded contrasting patterns across species and elements so that negative effects of heavy metals were masked to some extent by divergent tendencies across taxa. Only a marginally significant negative correlation between Cd concentration and the number of distress calls at handling (p = 0.09) was apparent overall, although this was significant in 4 of 6 species (p < 0.03). Thus, our results suggest that in heavy metal-polluted areas, exposure to potentially toxic metals such as Cd and Pb, which often co-occur and show strong correlations, could reduce the anti-predator responses of birds, indicating that the behavioral effects of heavy metals may vary depending on both species and the combined influence of different elements. As altering aggressive defensive behaviors in either direction (too much or too little) could adversely affect bird fitness, more studies are needed to understand the species-specific patterns. This study provides a foundation for future research on behavioral responses to handling obtained non-destructively to assess heavy metal contamination in polluted regions.