The level of extra-pair paternity (EPP) is extremely variable among avian species. Although a powerful interspecific database has been provided, further extra-pair paternity investigations on different species and populations in different environments are needed to advance our understanding of avian mating systems. Two passerine species living in same desert environment, the Isabelline Shrike (Lanius isabellinus) and Saxaul Sparrow (Passer ammodendri), are socially monogamous, but exhibit differences in many traits. We identified 6 polymorphic microsatellite loci for the Isabelline Shrike and 10 loci for the Saxaul Sparrow to estimate the rate of EPP. The results indicated that 4.92% of Isabelline Shrike broods (3/61) contained extra-pair offspring, with 1.46% of nestlings (3/ 206) being sired by extra-pair mates. Of the Saxaul Sparrow, 38.82% of broods (33/85) had at least one extra-pair offspring; the percentage of extra-pair offspring was 11.22% (44/392). In conclusion, these 2 passerines have different levels of EPP; however, these levels are comparable to those found in congeneric species.

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