Population trends of native and non-native forest birds on the island of Moloka‘i, Hawai‘i

Smith, Lauren; Judge, Seth; Genz, Ayesha; Berry, Lainie; Berthold, Laura; Mounce, Hanna; Camp, Richard

Hawai‘i’s avifauna has undergone profound changes over the past 1,000 years, with many endemic bird species driven to extinction and non-native introductions reshaping forest ecosystems. On the island of Moloka‘i, habitat degradation and the introduction of mosquito-borne disease, mainly avian malaria (Plasmodium relictum), have caused extinctions and severe declines in native forest bird populations. To assess these changes, point-transect distance sampling surveys were initiated in 1979 and 1980 and repeated six times, most recently in 2021, covering a 3,527 hectare area. This study analyzes species composition, population densities, abundances, and long-term trends for species with sufficient detections using log-linear regression. Since 1979–1980, a total of 17 non-native and 3 native species were detected across all six surveys. The non-native Warbling White-eye (Zosterops japonicus) had the highest density and abundance in every survey, while abundance of Red-billed Leiothrix (Leiothrix lutea) significantly trended upward. The Japanese Bush Warbler (Horornis diphone) irrupted in the survey area, increasing in abundance by more than 99% since 1979–1980. Among native species, ‘Apapane (Himatione sanguinea) populations increased by 33%, while Hawai‘i ‘Amakihi (Chlorodrepanis virens) declined by 78% from their peak in 1995. Federally threatened ‘I‘iwi (Drepanis coccinea), highly susceptible to avian malaria, have not been recorded on Moloka‘i since 2010, and the endemic Oloma‘o (Myadestes lanaiensis) has not been detected since 1980 and is possibly extinct. Our results underscore the ongoing conservation crisis for Moloka‘i’s forest birds and the continued vulnerability of native birds to disease and habitat loss.

Population trends of native and non-native forest birds on the island of Moloka‘i, Hawai‘i

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