Snail consumption and breeding performance of pied flycatchers (Ficedula hypoleuca) along a pollution gradient in the Middle Urals, Russia.

During the years 1989-91, 1997-2003, and 2005-07, we studied how emissions from the Middle Urals copper smelter affect snail availability and reproduction of free-living pied flycatchers (Ficedula hypoleuca). We counted snail shells dropped in nests and analysed food samples of nestlings. Pied flycatchers brought to nestlings fewer shells in heavily polluted sites compared to background sites, resulting in reduced Ca intake. Species diversity of snails collected by birds decreased with decreasing distance from the pollution source. The pattern was the same both in deciduous and coniferous forests. In sites closest to the smelter, 20-50% of breeding females suffered from Ca deficiency, which resulted in an increased proportion of deserted clutches and clutches with defective eggshells. Number of fledglings per nest decreased in heavily polluted sites, especially in broods with decreased snail supply. This study demonstrated that pollution can cause both direct effect of toxicants to birds and indirect effects via reduced Ca availability.