We present a preliminary list of the avifauna found at the Estação Ecológica do Cuniã (ESEC Cuniã) in Porto Velho, northern Rondônia, Brazil. This inventory is based on systematic records obtained by mist-netting and camera trapping and non-systematic visual and audio records collected within the study area in 2017 and 2019. The combined dataset includes 135 bird species representing 37 families. Among these species are endemic birds and migratory birds. Four of the species are described in the last decade, and the records represent expansions of these species’ known ranges to the state of Rondônia. Overall, the data show that the ESEC Cuniã has a considerable diversity of bird species and is important for the conservation of the fauna of the floodplains of the Amazon basin.