Apparent genetic monogamy in the Bewick's wren (Thryomanes bewickii)

Mixed reproductive strategies are common for many socially monogamous bird species. The levels of extra-pair paternity among passerine species are highly variable. Extra-pair paternity (EPP) has been documented for many socially monogamous birds including some members of the wren family (Troglodytidae), however, it has not been documented for the Bewick’s wren (Thryomanes bewickii) although extra-pair reproductive behaviors have been suggested. I collected genotype data from 71 nestlings and 20 putative parents making up 13 broods. The rate of EPP was assessed with the use of 6 cross-species microsatellite loci. Of 13 broods, 12 (92.31%) contained no extra-pair offspring. Of 71 nestlings, 66 (92.96%) were sired by their putative fathers and 5 (7.04%) were assigned to candidate fathers not likely to be the true father. Bewick’s wrens may follow a mixed reproductive strategy but remain mostly genetically monogamous, however, the result of EPP in 1 brood may be erroneous.