Do pipits use experimentally supplemented rich sources of calcium more often in an acidified area?

How birds respond to the recent phenomenon of calcium deficiency in acidified areas is still poorly known. This study, carried out in the Jeseniky Mountains (heavily polluted, acidified area in the Czech Republic), in alpine ecosystems of central Norway, and in the limestone part of the Mala Fatra Mountains (Slovak Republic), provides the first experimental evidence that birds select and bring supplemented calcium-rich items to their nestlings more often in an acidified area, Meadow Pipits Anthus pratensis and Water Pipits A. spinoletta selected calcium-rich items (mainly snail shells) from various materials placed near their nests and this selectivity did not differ between areas or species. Thinning of egg shells (8% at blunt pole, 5% at egg side) suggests that Meadow Pipits in the Jeseniky, Mountains were negatively influenced by the low calcium availability in spite of their ability to adjust foraging behaviour.