ИСТИНА

The ability of insectivorous birds to adjust the terms of provisioning chicks to the period of rich prey abundance is a key problem in the studies devoted to avian food ecology and impacts of global warming. In Moscow region, we studied the relation between temporal patterns of breeding pied flycatchers and caterpillar abundance in birch crowns. Caterpillars and other arthropods inhabiting birch crowns exhibit important food recourse for this migratory hole-nesting species in the study area. We estimated biomass of prey during 14 seasons by Tinbergen & Dietz (1994) method. For each season, the phase of high prey abundance included peak (P2) and interval between two half-peaks (P1-P3) calculated on the base of long-term peak median value. We described breeding temporal curves of pied flycatcher in quartiles. Spring temperatures influenced on start of mass flycatcher breeding, start of the phase of prey abundance (P1) and date of prey peak (P2), which led to correlation between these terms. There was no relation between the dates of completion of mass flycatchers’ breeding and finishing the phase of prey abundance. On average, mass hatching date of chicks occurred later than the date of prey peak, and the main fledging period covered the phase of decline of prey abundance (P2-P3). Even late mass portion of broods managed to leave their nests just before the completion of favorable provisioning period (P3). However, the equilibrium appears to be unsteady, and early termination of prey abundant phase resulted in low reproductive success of pied flycatcher population.