Extra-pair Paternity of Wood Warblers in the Pskov Region, Russia

BACKGROUND: Extra-pair paternity, 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 extra-pair paternity 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: To investigate the presence of extra-pair paternity in a Wood Warbler population in the Pskov Region, Northwest Russia. MATERIALS AND METHODS: During fieldwork, we collected 124 DNA samples from 27 adult males, 14 adult females,and 83 chicks from 14 families. To analyze extra-pair paternity, we used three microsatellite loci (Ase5, Ase18, Ase27) suitable for this population. RESULTS: Of the 14 socially monogamous families examined, extra-pair paternity was found in one brood, where two of five chicks (40%) were sired by a male outside the social pair bond. The overall extra-pair paternity rate was 2.5%, and 7.1% of nests contained extra-pair young. These rates are markedly lower compared to Central Russia, where extra-pair paternity 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 extra-pair paternity in the Pskov Region may be linked to lower breeding densities and fewer unmated males. It cannot be also ruled out that the extra-pair paternity estimate is underestimated due to the use of an insufficient number of markers. Further studies are essential to assess extra-pair paternity in various regions and to understand the ecological and behavioral factors that influence its prevalence.