Distribution and abundance of forest birds in low-altitude habitat on Hawai'i Island: evidence for range expansion of native species

Abstract

The Hawaiian honeycreepers are thought to be limited primarily to middle- and high-altitude wet forests due to anthropogenic factors at lower altitudes, especially introduced mosquitotransmitted avian malaria. However, recent research has demonstrated that at least one native species, the Hawai'i 'Amakihi ( Hemignathus virens virens ), is common in areas of active malaria transmission. We examined the current distribution and abundance of native and exotic forest birds within approximately 640 km 2 of low-altitude (0–326 m) habitat on south-eastern Hawai'i Island, using roadside variable circular plot (VCP) at 174 stations along eight survey transects. We also re-surveyed 90 stations near sea level that were last surveyed in 1994–1995. Overall, introduced species were more abundant than natives; 11 exotic species made up 87% of the total individuals detected. The most common exotic passerines were Japanese White-eye ( Zosterops japonicus ), House Finch ( Carpodacus mexicanus ) and Northern Cardinal ( Cardinalis cardinalis ). Two native species, Hawai'i 'Amakihi and 'Apapane ( Himatione sanguina ), comprised 13% of the bird community at low altitudes. Hawai'i 'Amakihi were the most common and widespread native species, being found at 47% of stations at a density of 4.98 birds/ha (95% CI 3.52–7.03). 'Amakihi were significantly associated with 'ohi'a ( Metrosideros polymorpha )-dominated forest. 'Apapane were more locally distributed, being found at only 10% of stations. Re-surveys of 1994–1995 transects demonstrated a significant increase in 'Amakihi abundance over the past decade. This work demonstrates a widespread recovery of Hawai'i 'Amakihi at low altitude in southeastern Hawai'i. The changing composition of the forest bird community at low-altitudes in Hawai'i has important implications for the dynamics of avian malaria in low-altitude Hawai'i, and for conservation of Hawai'i's lowland forests.