When dates disagree: radiocarbon and sighting-based models reveal range-wide variability in great auk (Pinguinus impennis) extinction estimates

Methods for inferring extinction are well established for events that either occurred on millennial time scales (e.g. the late Quaternary) or are unfolding in the present. However, these methods employ distinct data types inherent to palaeontological or neontological settings, yielding a potentially disjointed view of the extinction process. We leveraged the historical extinction of the great auk (Pinguinus impennis)-a large, flightless seabird native to the Atlantic-as a test case to assess the effects of using varied data types (286 quality-scored occurrences) and models (Gaussian-resampled inverse-weighted McInerny, Solow and Beet) in inferring extinction across centennial time scales. While the last confirmed great auk was killed in 1844 CE in Iceland, the dynamics of species-wide range collapse in response to differing harvest practices have not been explored. Our sighting-based estimates suggest the species may have persisted a decade longer (1860 CE) in the Northwest Atlantic, highlighting the need for future research on this understudied portion of their range. Radiocarbon-based models estimate extinction later (post-2000 CE) across the species' range, suggesting that inherent uncertainties in radiocarbon dates and their calibration-particularly for marine samples-may constrain their applicability for detailing extinction processes on conservation-relevant time scales.