Pale-headed Brush-finch Atlapetes pallidiceps is on the verge of extinction, with fewer than 100 individuals surviving in an area of less than 4 km2 in the Yunguilla valley in the province of Azuay, southern Ecuador. A reserve created for the protection of the species held 10 or 12 pairs in 1999, 14 in 2000, 16 in 2001 and 17 in 2002. Nearly all males had distinctive songs, showing little or no change from one year to the next. The yearly turnover of singing males was 40% in both 2000 and 2001 (4/10), and 29% in 2002 (4/14). Altitudinal range of A. pallidiceps was 1,650–1,950 m. Habitat was typical of regenerating landslides and fallow fields, composed of early succession growth in the ecotone between dry, thorny valley-bottom and humid forest remnants on the upper slopes. Territory size averaged 1.0 ha (range 0.7–1.4 ha, n = 37), and nearly all territories were within 100 m of a stream or an irrigation channel. Most were on steep slopes with Chusquea bamboo, and deciduous bushy cover with few or no spines, typically including the composite Steiractinia sodiroi, and with some open areas. Although habitat improved considerably between 1999 and 2002, some territories were vacant some years. Shiny Cowbird Molothrus bonariensis parasitism was noted, and could be even more important than habitat as a limiting factor of the population size. The song of A. pallidiceps was found to be similar to songs of several other Atlapetes spp. in general pattern. Diet was composed of arthropods, fruit and a few seeds. Arthropods were almost invariably picked from the bark on upper- and under-surfaces of twigs and small branches. Seeds were taken from the ground. Young (cowbirds) were apparently only fed insects. Between 1,800 and 1,950 m A. pallidiceps occurred with Rufous-naped Brush-finch A. latinuchus, which replaces it at higher elevations. Territories did not overlap, and where they met, A. latinuchus was confined to slightly taller and more humid vegetation, or to forest. In interspecific encounters A. pallidiceps was subordinate to Stripe-headed Brush-finch Buarremon torquatus, with which it coexisted in all its territories. Habitat management began in 2002, and limited cowbird control is planned to begin in 2003.