Eighteen species of Amazonian birds have been considered river-island obligates in northeastern Peru, but some of these species have been detected recently at mainland sites along the Amazon River. We document the presence of supposed river-island obligate birds at riparian sites on the mainland and characterize these birds' habitat use on the islands and the mainland on the basis of point counts at five island sites, five riparian mainland sites, and five upland mainland sites. We regularly encountered seven species of supposed river-island obligates on the islands and four of them, including the Ash-breasted Antbird (Myrmoborus lugubris), Black-and-white Antbird (Myrmochanes hemileucus), Castelnau's Antshrike (Thamnophilus cryptoleucus), and Fuscous Flycatcher (Cnemotriccus fuscatus), also occurred regularly at the riparian mainland sites, but none occurred at the upland mainland sites. These four species are primarily birds of early-successional scrub or forest, but they also used agricultural habitats on both the islands and the mainland. The presence of these species on the mainland may have been overlooked by previous researchers, who may neglect human-dominated habitats during avifaunal surveys, or these species may have only recently colonized the mainland in response to an increase in the amount of small-scale agricultural plots in the region. Supposed river-island obligate birds are, in fact, habitat specialists, and can occur on the mainland if appropriate natural or anthropogenic habitat exists there. Human-dominated tropical landscapes may provide habitat suitable for disturbance-adapted bird species and should not be overlooked during avifaunal surveys.