Loyal as a robin: Low frequency of extra-pair paternity in European robin population in the primeval forest of Białowieża National Park

Abstract

Although the robin is a quite common Eurasian bird, little is known about the phenomenon of extra-pair paternity (EPP) within this species, mainly due to its extremely secretive behavior during the breeding season. This study for the first time reveals the level of EPP of the continental subspecies under the primeval forest condition. To analyze the EPP frequency, genetic methods were used (microsatellite genotyping). Three research plots (~30 ha each) were established in a lime-hornbeam and riverine forest, in Białowieża National Park (north-eastern Poland) - the most primeval, lowland forest in the entire temperate zone. The study was conducted in 2018-2019 during the robin’s breeding season (late March - late June) using a combined mapping technique. Upon locating the nests, tail feathers, which were used as a source of DNA, were collected from entire robin families, including adults captured via mist nets. In total genetic material was obtained from a total of 70 robin families. Genotypes of social parents were compared with genotypes of nestlings to assess the occurrence of EPP and identify extra-pair males. We found evidence of EPP in 5.7 % of nests. Accordingly, 5.1 % of nestlings were the offspring of extra-pair males. We accept the assumed hypothesis of the low frequency of extra-pair paternity in the European robin population under the primeval forest condition. The explanations for the low level of EPP can be found in the robins begging behaviour in the pre-breeding period and the female constraint theory.