Long-Term Population Trajectories and Recent Change of East Maui Landbird Communities

Judge, Seth; Warren, Christopher; Bak, Trevor; Camp, Richard; Vallocchia, Sonia; Mounce, Hanna

doi:10.36967/2320164

The distribution, abundance, and population trends of landbirds on East Maui were assessed from the point-transect distance-sampling surveys conducted in 2022 across four regions: Haleakalā National Park (HALE), Kula, Leeward, and Windward. Surveys were designed to evaluate short-term population change (2017–2022) for all species and long-term trajectories (1980–2022) for Maui island endemic forest birds. A total of 30 landbird taxa were detected, including 9 native and 21 non-native species. Native forest birds were most widespread and abundant in the predominantly native forests of the HALE and Windward regions, whereas non-native species richness, occurrence, and detection rates were highest in the mixed native and non-native forests and grasslands of the Kula and Leeward regions. ʻApapane (Himatione sanguinea) and Hawaiʻi ʻAmakihi (Chlorodrepanis virens wilsoni) were the most frequently detected native species, occurring at 88% and 90% of stations with detection rates of 6.64 and 2.74 birds per count, respectively. Maui ʻAlauahio (Paroreomyza montana) were detected at 33% of stations, with the highest occurrence in the HALE Region (69%; 1.25 birds per count). ʻĀkohekohe (Palmeria dolei) occurred at 9% of stations overall, with detections concentrated in high-elevation (>1,500 m) mesic and montane ʻōhiʻa lehua (Metrosideros polymorpha) forest. There were only six detections of the critically endangered Kiwikiu (Pseudonestor xanthophrys). Three non-native species—Warbling White-eye (Zosterops japonicus), Japanese Bush Warbler (Horornis diphone), and Red-billed Leiothrix (Leiothrix lutea)—were widely distributed across all regions and co-occurred with native forest birds. Sufficient detections were obtained to estimate densities for ten species (six native and four non-native). Short-term population change was evaluated by comparing 2017 and 2022 density estimates using two-sample z-tests within an equivalency-testing framework. ʻApapane and Hawaiʻi ʻAmakihi densities increased significantly in the HALE and Windward regions but declined significantly in the Leeward and Kula regions. Maui ʻAlauahio densities increased significantly in HALE, while changes elsewhere were negative but the difference was inconclusive. No significant short-term change in Kiwikiu density was detected. In contrast, ʻĀkohekohe densities increased significantly in HALE, contributing to a range-wide increase. Long-term trajectories indicate that all three Maui island endemic species increased through the 1990s before undergoing sustained declines. Kiwikiu, previously estimated at more than 400 individuals through 2012, was estimated at fewer than 170 individuals in 2022 (upper 95% CI). ʻĀkohekohe declined 72% from nearly 12,000 birds in 2000 to fewer than 3,400 individuals, while Maui ʻAlauahio declined 73% from a late-1990s peak of approximately 214,500 birds to about 57,100 birds. These declines coincided with the upward expansion of avian malaria (Plasmodium relictum) and its mosquito vector (Culex quinquefasciatus) under warming temperatures. The 2022 survey provides a critical baseline for evaluating the effectiveness of recently implemented landscape-scale mosquito control and future population responses of Maui’s remaining native forest birds.

Long-Term Population Trajectories and Recent Change of East Maui Landbird Communities

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