Spatial Distribution of Bird Species on the East Flank of Mauna Loa

Abstract

Eleven transects in ten different types of plant communities found along an altitudinal gradient on the east flank of Mauna Loa were sampled monthly using the "count x detectability" method of censusing birds. Eight of these sites were on the Mauna Loa Transect, which has been intensively sampled by IBP participants in the Island Ecosystems IRP. Frequency, density and distribution of the 29 bird species encountered are discussed. Data on species presence and density at each site were used to construct community (sampling site) ordinations based on similarity indices and species ordinations based on two-way tables. The results of these analyses provided the basis for the objective definition of transect zones for those sites located on the Mauna Loa Transect. The transect zones objectively defined by avian community analyses were almost identical to those based on analyses of plant communities on Mauna Loa. The habitats selected by each bird species are discussed. Optimum habitats as a reflection of maximum density are described for each species. At least two types of environmental factors associated with the altitudinal gradient appear to be important influences on patterns of avian spatial distribution: 1) continuously varying environmental factors (e.g., rainfall, temperature, gradual transitions from one plant community to another); 2) habitat discontinuities (narrow ecotones, abrupt changes in vegetation structure). Competition is briefly discussed as a factor that may affect density and distribution of some bird species. In some cases (e. g., 'Apapane, 'I’iwi) it is apparent that very specific factors (e.g., blooming time and amount in certain important food plants such as Metrosideros and Sophora) strongly influence the distribution and local abundance of a few bird species. However, vegetation structure appeared to be the single most important influence on population density and patterns of spatial distribution of the bird species studied.