Scales of Habitat Selection by Foraging 'Elepaio in Undisturbed and Human-Altered Forests in Hawaii

Abstract

I examined habitat selection by foraging 'Elepaio (Chasiempis sandwichensis) in relatively undisturbed and human-altered forests in Hawaii at three hierarchically-nested scales by comparing birds with random sites. The fine scale was based on a sphere with a radius of 0.75 m, the intermediate scale used a cylinder from ground to canopy with a radius of 1.5 m, and the broad scale was based on the point-quarter method. At a fine scale, 'Elepaio in both forests selected foraging sites with high foliage density, large bark surface area, and many twigs and branches. 'Elepaio in disturbed areas compensated for lower available foliage density by being "hyperselective" toward high density sites. At an intermediate scale, 'Elepaio in both forests favored sites with above average foliage density at all heights. Birds in undisturbed habitat preferred sites with native ground cover and used sites with feral pig damage or exotic grasses less than expected, while birds in disturbed forest did not favor any ground cover type. At a broad scale, tree and shrub densities were much lower in disturbed areas, but 'Elepaio did not select sites with high tree or shrub density in either forest. 'Elepaio in both forests preferred 'Ohia, and used Koa less than expected. Disturbed areas may be lower quality foraging habitat because less space consists of sites with preferred high fine-scale foliage density. The broad scale is commonly used to measure habitat around nest sites and song perches, but it did not detect patterns of foraging site selection and may be too coarse for measuring foraging habitat of forest birds.