Extrapair copulations reduce inbreeding for female red-backed fairy-wrens, Malurus melanocephalus

► A benefit of extrapair mating in philopatric species is inbreeding avoidance. ► Red-backed fairy-wrens have significant local genetic structure. ► Female fairy-wrens cheat when they are paired to more closely related males. ► Extrapair offspring are more heterozygous than their within-pair half siblings. ► An experimental test in the field confirmed correlative results.