An avifaunal survey was carried out at Bukit Balingkadus Forest Reserve in Ranau, Sabah, Malaysia. The MacKinnon List method was used to assess species diversity. The four-day survey recorded a total of 16 MacKinnon lists with 388 individuals detected. A total of 86 species from 37 families were recorded, with H=3.89 and EH=0.65. True species richness was estimated (using SuperDuplicates® online calculator) to be approximately 114 species, with approximately 28 species not detected. There were 13 species of Bornean endemics, two of which were listed as Vulnerable in the IUCN Red List of Threatened Species. Pycnonotidae was the most speciose family with 10 species. Cuculidae and Megalaimidae were ranked second with 6 species each. Zosteropidae had the highest number of individuals at 47. The top ten most detected species made up 49.5 % of all species detected. The most detected species was the Chestnut-crested Yuhina (Zosteropidae). The majority of the species detected (81) were forest-dependent, of which 60 were strictly forest birds. Insectivores made up the most dominant dietary guild, i.e., a total of 41 species (from 22 families). Frugivores ranked second with 29 species from 10 families.