Ecology and Breeding Biology of the Hawaii Elepaio (Chasiempis sandwichensis bryani)

Abstract

Elepaio (Chasiempis sandwichensis bryani) were studied on the island of Hawaii from 1970 through 198 1. The species had a protracted breeding season from February through August, with most intensive breeding from April to June. Annual breeding season length varied among years (range 3-7 months). Elepaio retained mates for more than one season and remained in their territory throughout the year. An Elepaio territory encompassed the nest site, all food resources, and had similar boundaries in succeeding years. Nests were statant, open-cupped, with mamane (Sophora chrysophylla) trees the preferred nesting sub- strate. Clutch size of 23 nests was two eggs and did not vary among years. Both parents incubated, brooded, and fed the young. Incubation periods averaged 18 (range 17-l 9) days; hatching success of eggs incubated to term in 22 nests was 75%. Nestling periods averaged 15.6 days; fledging success was 89.3% and young fledged synchronously. Total reproductive success, based on 19 nests with complete records, was 65.8%. The most important factor that influenced annual Elepaio productivity on Mauna Kea was length of the breeding season, followed by the number of nesting birds and eggs laid that failed to hatch (25%). Inter-island subspecies comparisons revealed many similar behaviors (e.g., courtship chasing, territory type, clutch and egg sizes, nest placement, adult roles in nest building, incubation, brooding and feeding). Differences among subspecies appeared to revolve mainly around the influences of forest-type in which birds bred. In mesic habitats on Oahu and Hawaii, predation of eggs and young by introduced mammals played a major role in decreasing annual productivity, whereas in the dry forest of Mauna Kea predation on C. s. bryani nests was much lower.