Diet composition as a cause of different contaminant exposure in two sympatric passerines in the Middle Urals, Russia

•We examined the diet composition and metal concentrations in preys of two passerines.•The proportion of caterpillars and spiders increased in bird diets in the polluted area.•Spiders and molluscs showed highest metal concentrations, and caterpillars the lowest.•The proportion of metals provided to birds by spiders exceeded their dietary fraction.•An increased dietary proportion of caterpillars reduces contaminant exposure.

Contaminant exposure can vary between species but primary causes of it are often unclear. In order to estimate heavy metal intake of two sympatric passerines – Ficedula hypoleuca Pall. and Parus ater L. – we studied nestling diet and metal concentrations in prey invertebrates, near the Middle Ural copper smelter and in an unpolluted area. Diet of P. ater contained more Cu, Cd and Zn compared to F. hypoleuca and the same amount of Pb. Contribution of different prey taxa to bird metal intake was not equal to their dietary proportion. Proportion of Cu, Zn, Pb and Cd provided to birds by spiders and molluscs, as well as Cd and Pb provided by ants and imagoes Diptera, exceeded their dietary fraction by several times. In contrast, the contribution of Lepidoptera and sawfly larvae to bird metal intake was less than their dietary proportion. Pollution-related changes in the diet modified bird contaminant exposure along with pollutant concentrations in preys.