Urban metal pollution explains variation in reproductive outputs in great tits and blue tits

It is regularly reported that avian reproductive outputs are reduced in urban areas, yet the underlying reasons for discrepancies between and natural habitats to date poorly explained. To address this knowledge gap, we tested whether of wild great tit (Parus major) blue (Cyanistes caeruleus) populations Warsaw (Poland) correlated with concentrations six main metallic/metalloid trace elements (MTEs; copper, zinc, lead, cadmium, arsenic mercury) three types biological material pertaining reproduction: nestling feathers, nest droppings. For first time, our study highlights consistent negative effects copper feathers on fledging success mass both tits tits. Fledging was also negatively cadmium lead Importantly, while relative proportions each MTE were equivalent materials, better than two other materials; result suggests absorption would explain part variation individual fitness emphasises relevance using investigating exposure nestlings hole-nesting birds. Altogether, results suggest pollution likely contributes differences observed living more environments.