ИСТИНА

The Pied Flycatcher breeding population was monitored in the Moscow region during 23 years (1988-2010). The abundance of caterpillars, an important food resource of this insectivorous species, was surveyed in canopies of birch trees from 2002-2010. Long term changes in spring weather conditions, the dynamics of Pied Flycatcher breeding numbers and factors influencing both characteristics of the population and individual breeding success were studied. In contrast to western European study areas, the Moscow region was not characterized by warming springs during the last two decades. Warming in the second half of April (the time of arrival of the first portion of flycatchers) was often combined with a fall in temperature in mid May (the time when first eggs were laid in first nests). A combination of weather conditions in the end of April and in May shaped the population curves of breeding dates. These curves changed from year to year but did not perform any stable trend. The start of mass breeding (when first eggs were laid by the first quarter of breeders) was affected both by temperatures in the first half of May and the value of maximal abundance (peak) of caterpillars, the latter index not being directly related to spring weather conditions. Breeding seasons were longer in the years with delayed peaks of caterpillars. In the models where environmental factors (weather and food conditions) and individual quality of breeders (breeding experience) were included as independent variables, breeding success was mainly affected by environmental conditions.