Montane riparian areas across the Sky Island region of the southwestern United States and northwestern Mexico contribute disproportionally to biodiversity at local and regional scales. We explored how composition and structure of vegetation influenced species richness and community composition of songbirds breeding in riparian areas of southern Arizona. We surveyed birds and vegetation during two breeding seasons at 45 stations established across three riparian canyons in two mountain ranges. Species richness of songbirds increased as volume of understory vegetation, density of Arizona sycamore (Platanus wrightii), and density of alligator juniper (Juniperus deppeana) increased; species richness decreased as density of Acacia and Mimosa species increased and oak (Quercus) trees increased. Composition of breeding bird communities was structured along an elevation and vegetation gradient, from open-canopy desert scrub to closed-canopy oak woodlands. Richness and composition of breeding bird communities in these biologically diverse montane riparian canyons were governed by both floristic composition and physical structure of dominant riparian vegetation.