The sliver of humid tropical and montane forest on the east slope of the Andes in Ayacucho Department ranks among the least surveyed sectors of the Peruvian Andes. This mountainous region, along with adjacent Apurímac Department and western Cuzco Department, comprise the Apurímac River Valley, a putative biogeographic barrier. Hence, understanding avian distributions in the vicinity of the Apurímac River Valley is fundamental to understanding faunal turnover across it. Here, we report results of recent avifaunal surveys (2008–2012) from five sites in the Apurímac Valley region. We report 35 bird species previously undocumented in Ayacucho, six of which represent range extensions, including records of the endemic Black-spectacled Brush-Finch (Atlapetes melanopsis), Marcapata Spinetail (Cranioleuca marcapatae), and Chestnut-breasted Mountain-Finch (Poospiza caesar); the remaining records filled perceived range gaps. Specimen evidence suggests little phenotypic introgression between differentiated forms across the region, except for apparent introgression zones in Superciliaried Hemispingus (Hemispingus superciliaris) and Mountain Cacique (Cacicus chrysonotus); these observations uphold the idea that the Apurímac River Valley functions to isolate bird populations. Specimens of two Grallaria sp. and one Scytalopus sp. may represent new taxa, two of which appear to be endemic to Ayacucho (the third extends into adjacent Junín Department). More generally, montane forest bird species richness and avian endemism in eastern Ayacucho are similar to those of Cuzco and Pasco departments; previous assessments that considered Ayacucho as an area of reduced diversity were misled by sparse sampling effort.