Estimated dates of recent extinctions for North American and Hawaiian birds

Abstract

Series of sighting records - the years in which a species has been recorded - can be used to infer whether species have gone extinct, and when extinctions occurred. We compiled sighting records for 52 rare bird species, subspecies, and distinct island populations from North America and Hawaii, 38 of which proved adequate for such analyses. Using a data set that combines non-controversial sight records with those for which physical evidence exists, no populations were judged likely to be extant, including those that have not been declared extinct. The 'alalawas the only species with a 95% confidence interval around the extinc- tion date that extended beyond 2009, suggesting that this population is the least unlikely to be extinct. Although all are probably extinct, populations were ranked according to their likelihood of persistence, so that any future searches can be prioritized to minimize the risk that resources are spent on extinct spe- cies. Estimated extinction dates spanned the period from the 1840s-2000s, with evidence for a peak in the early 1900s. On average, only about 4 years passed between a species' last sighting and its estimated extinc- tion date, and the 95% confidence intervals around extinction dates extended 9-26 years after the last sight- ing. Long gaps between sightings were very rare. Mean and median gap sizes between consecutive sightings within sighting records were 2.5 and 0 years, respectively. Gaps between the last and penultimate sightings were smaller than average gap sizes earlier in sighting records. Finally, a non-parametric method that can be calculated with more limited data proved a weak substitute for using more complete sighting records.