Extra-pair paternity in Wood Warblers: preliminary findings from the Pskov Region, Northwest Russia

BACKGROUND: Extra-pair paternity (EPP), where offspring are fathered by males outside of a primary pair bond, is common among avian species and challenges the idea of strict monogamy. It provides insights into sexual selection and reproductive strategies. While EPP is frequently documented in species such as the Willow Warbler, its occurrence and population variability in the closely related Wood Warbler remains poorly studied.

AIM: This study investigated the presence of EPP in a Wood Warbler population in the Pskov Region, Northwest Russia.

MATERIAL AND METHODS: During fieldwork, we collected 124 DNA samples from 27 adult males, 14 adult females, and 83 chicks from 14 families. To analyze EPP, we used three microsatellite loci (Ase5, Ase18, Ase27) suitable for this population.

RESULTS: Of the 14 socially monogamous families examined, EPP was found in one brood, where two of five chicks (40%) were sired by a male outside the social pair bond. The overall EPP rate was 2.5%, and 7.1% of nests contained extra-pair young. These rates are markedly lower compared to Central Russia, where EPP in Wood Warblers has been documented at 25%, with 41% of nests containing extra-pair offspring. However, due to the small number of markers used, our estimates may be conservative. These results are therefore preliminary and require further investigation.

CONCLUSIONS: The reduced incidence of EPP in the Pskov Region may be linked to lower breeding densities and fewer unmated males. It cannot be also ruled out that the EPO estimate is underestimated due to the use of an insufficient number of markers. Further studies are essential to assess EPP in various regions and to understand the ecological and behavioral factors that influence its prevalence.