GoKawiilStudy: birds wait median 36 years after last sighting before being declared extinct
An analysis of 13 bird species and subspecies with documented last-sighting and extinction-declaration dates finds a median gap of 36 years, and a mean of 47.5 years, between the two. The shortest gap was three years, for the dusky seaside sparrow; the longest was 124 years, for the Kauaʻi nukupuʻu, not delisted by the US government until October 2023. Four additional birds with last records between 1935 and 1963 have never been formally declared extinct.