Pacific Island landbird monitoring report, Hawaiʻi Volcanoes National Park, 2015-2016: Tract groups 1 and 2

Hawaiʻi Volcanoes National Park (HAVO) was surveyed for landbirds and landbird habitat from February through April 2015 and February through April 2016. This information provides the second datum in the time-series of Pacific Island Network (PACN) monitoring for long-term trends in landbird distribution, density, and abundance. Initial PACN surveys were conducted in 2010 and are repeated every five years. 

The entire survey area was comprised of eight tracts in forest, woodland, and shrub habitat, totaling 26,364 ha. Each tract was surveyed using point-transect distance sampling to calculate estimates of bird abundance and density. In addition to the permanent PACN survey transects, randomly generated point-transects were also surveyed, allowing for a split panel sampling design. 

A total of 14,061 bird detections of twenty-eight species were recorded during point counts; 8 species were native to Hawaiʻi and 20 species were non-native. ʻApapane (Himatione sanguinea) and Hawaiʻi ‘Amakihi (Chlorodrepanis virens virens) were the most abundant and widely distributed native species detected. ‘Ōma’o (Myadestes obscurus), ‘I‘iwi (Drepanis coccinea), and Hawaiʻi Elepaio (Chasiempis sandwichensis) occurred at fewer than 30% of the 757 stations surveyed, and were absent from some tracts. Three species of native birds detected during surveys were endangered—ʻIo (Buteo solitarius), Hawaiʻi Creeper (Loxops mana), and Hawaiʻi ʻAkepa (Loxops coccineus). Two additional endangered species were detected incidentally on transects—Nēnē (Branta sandwicensis) and ʻAkiapolaʻau (Hemignathus wilsoni). Non-native Japanese White-eye (Zosterops japonicus), Northern Cardinal (Cardinalis cardinalis), Japanese Bush Warbler (Horomis diphone), and Yellow-fronted Canary (Crithagra mozambica) were detected throughout most tracts and had the highest relative abundances among non-natives. The remaining species detected occurred at less than 10% of stations surveyed. 

Sufficient detections to allow density estimation were made for 11 species (5 native and 6 non-native). Changes in species-specific densities by tract were assessed between the initial and current surveys using two-sample z-tests in an equivalence testing framework to determine long-term trends. Differences between densities were highly variable for native species; including increasing, decreasing and stable trends. There were notable increases of ‘I‘iwi and ‘Ōma’o densities in some tracts. However there were also declines of ‘Ōma’o in three tracts, including leeward Northwest Kahuku where birds were detected in 2010 for the first time in over 30 years, but not during this recent survey. ‘I‘iwi densities increased in the high elevation Pāpā tract; however, they declined in the Mauna Loa Strip tract where the species may be vulnerable to avian malaria. 

Trend results for Hawaiʻi ʻAkepa were inconclusive, but the species occurred at more survey stations than in 2010, and we estimate a density of 0.31 ±0.34 birds/ha in the 10,989 ha Kahuku tract. Hawaiʻi Creeper had in an increasing trend in the Kahuku tract with a density of 0.16 ± 0.07 birds/ha and an inconclusive trend in Honomalino, where there was only one detection in 2016. There was a large expansion in the distribution and abundance of the non-native Yellow-fronted Canary and Japanese Bush Warbler. The Lavender Waxbill (Estrilda caerulescens) was detected in HAVO for the first time. Trend results were variable for other non-native species, but generally maintained stable densities when compared to previous landbird surveys. Several habitat variables were sampled at monitoring stations in each tract. Canopy and understory species were predominantly native, especially in tracts where ungulates have been excluded.