Variation in the Body Condition of Pied Flycatchers Ficedula hypoleuca breeding in Vicinities of the Middle Ural Copper Smelter

The body condition of pied flycatchers breeding near the Middle Ural copper smelter (MUCS) and in the background area was analyzed in 1996–2023, a period of significant reduction in industrial emissions. 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 probably due to the forcing 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 decreased with increasing date of breeding (females only), air temperature at the chick feeding stage, and brood size (both females and males).