Cross-decades stability of an avian hybrid zone

It was postulated that hybrid zone between Townsend's Warblers (Setophaga townsendi) and Hermit Warblers (S. occidentalis) in the Washington Cascades has been moving from northern S. townsendi southwards towards S. occidentalis. However, no genomic test has been made on this hypothesis. We tested whether hybrid zone position moved over 2–3 decades by tracking nuclear genomic variation across the hybrid zone over two sampling periods (1987–94 and 2015–16).