Determining whether species have gone extinct requires considering the timing and reliability of records, the timing and adequacy of surveys, and the timing, extent and intensity of threats. However, previous assessments have either applied qualitative approaches or considered only the first of these factors. We applied quantitative methods encompassing all three factors to a suite of 61 potentially or confirmed extinct species of birds. We tested six different methods, each with a range of thresholds, for assigning species to IUCN Red List Categories, and compared the results with species' current categories.