On the Issue of the Primary Sex Ratio in the Pied Flycatcher (Ficedula hypoleuca)

Abstract

An assessment of the primary sex ratio in the local pied flycatcher population in South Karelia (Russia) is given, and its variations in broods depending on breeding characteristics and characteristics of the parents are analyzed. The proportion of males in 30 clutches examined in 2012 did not differ from the proportion of females and amounted to 50.8% of the total number of eggs laid (n = 199), although it varied from 14.3% to 85.7% in individual nests. A weak positive correlation between the proportion of males in the brood and the timing of breeding and the ornamentation of the feathers that form the white spot on the male’s wing (the first tertiary and the 5–6th upper greater coverts of the secondary feathers), and a negative correlation with the length of the wing and the third primary feather of the female were shown. Analysis using generalized linear models showed a significant relationship of the primary sex ratio in the brood only with the length of the female’s third primary feather. Possible mechanisms of changes in the sex ratio in broods are discussed.