Variability of body condition of the pied flycatcher Ficedula hypoleuca breeding in the vicinity of the Middle Ural copper smelter

The variability of the body condition of pied flycatchers breeding near the Middle Ural copper smelter (MUCS) and in the background area in 1996–2023, a period of significant reduction in industrial emissions, was analyzed. The body condition index (BCI) of females was not related to the level of environmental pollution. The lower BCI of males near the MUCS compared to the background area was apparently due to the displacement of the low-quality individuals into transformed habitats. The BCI of yearlings was less than that of older birds, especially in females incubating early and late clutches. The BCI of incubating females increased with increasing clutch size and breeding density. The BCI of birds decreased with increasing date of breeding (females only), air temperature at the nestling stage and brood size.