Sampling localities and geographic distribution of Z. borbonicus plumage morphs in Réunion and Mauritius, the two largest Mascarene Islands. Light, medium and dark grey layers on maps correspond to elevations 0-600 m, 600-1000 m, and 1000-3000 m, respectively. Thick lines correspond to sharp contact zones between morphs with narrow hybrid zones at rivers or lava flows. Thin black lines represent approximate boundaries between morphs away from contact zones (where considerable intergradation occurs). Dashed line indicates inferred boundary in unsurveyed area. Plumage morphs are coded as follows: A = brown, B = grey, C = grey-headed brown, D = grey-headed brown nape, E = Mauritius grey.