Nest usurpation is a behavior where one individual takes over the active nest of another individual of the same or a different species. The Grayish Baywing (Agelaioides badius) has been reported as an occasional inter-specific nest usurper. In previous studies, researchers have reported usurpation of nests of House Wrens (Troglodytes aedon) by Grayish Baywings. In this paper, we report that nest usurpation by Grayish Baywings is the second cause of breeding failure in a population of House Wrens in the Central Andes.