Status of Forest Birds in Hawaiʻi Volcanoes National Park: Mixed Results for Native and Non-Native Species

Judge, Seth; Paxton, Kristina; Beck, Angela; Camp, Richard

doi:10.36967/2318341

Hawaiʻi Volcanoes National Park (HAVO) was surveyed for landbirds and landbird habitat in 2020 and 2021 as part of a long-term monitoring program. These surveys represent the third data point in a time series assessing landbird distribution, density, and abundance. Surveys were conducted across seven tracts totaling 15,375 ha using point-transect distance sampling to estimate population density and abundance. A total of 29 species were detected, including eight native and 21 non-native species. Changes in species-specific densities by tract were evaluated using two-sample z-tests within an equivalence testing framework to assess population change relative to surveys conducted in 2010. Results were mixed across tracts for most native species. ʻApapane (Himatione sanguinea) densities increased significantly in four tracts but decreased in the remaining three. Hawaiʻi ʻAmakihi (Chlorodrepanis v. virens) densities increased in the two largest tracts—Mauna Loa South Flank and Mauna Loa Strip—but decreased in the East Rift Zone and ʻŌlaʻa tracts, where the species has remained at low densities (<0.30 birds/ha) since 2010. Hawaiʻi ʻElepaio (Chasiempis sandwichensis) showed increases in the Honomalino, ʻŌlaʻa, and Pāpā tracts, but decreased by more than 60% in the Mauna Loa Strip and was absent from the Mauna Loa South Flank. The federally threatened ʻIʻiwi (Drepanis coccinea) was absent from the Mauna Loa Strip, where an estimated 2,417 ± 32 (SE) individuals were present in 2010, and was also undetected in three additional tracts where it had previously occurred. In contrast, ʻIʻiwi density increased significantly in the Honomalino tract, with an estimated 2021 abundance of 1,366 ± 26 birds. Differences of ’Ōma’o (Myadestes obscurus) were also mixed, with a notable increase in the Mauna Loa South Flank tract where we estimated an abundance of 3,035 ± 23 birds. Patterns also varied among non-native species. The Warbling White-eye (Zosterops japonicus) was the most abundant and broadly distributed non-native species, though densities declined significantly in five tracts. After being undetected in 2010, densities of the Japanese Bush Warbler (Horornis diphone) increased significantly in most tracts. The Northern Cardinal (Cardinalis cardinalis) and Red-billed Leiothrix (Leiothrix lutea) also increased across most surveyed areas. These findings highlight the continued vulnerability of native landbirds in HAVO to habitat degradation, invasive species, non-native predators, avian disease, and wildfire.

Status of Forest Birds in Hawaiʻi Volcanoes National Park: Mixed Results for Native and Non-Native Species

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