Those were just the studies I could find offhand of monogamous species with no EPCs. If you include EPCs, about 90% of birds are socially monogamous[1]. According to [2] ~25% of those species are genetically monogamous (i.e. no EPCs). Though I should mention that genetic monogamy is a pretty high bar, which humans do not pass by a long shot. Is this sufficient evidence for you?<p>[1]Lack, D. 1968. Ecological Adaptations for Breeding in Birds. Methuen and Company, London.<p>[2]Griffith, S. C. , I. P F. Owens , and K. A. Thuman . 2002. Extra-pair paternity in birds: A review of interspecific variation and adaptive function. Molecular Ecology 11:2195–2212.