Movement Patterns of a Native and Non‐native Frugivore in Hawaii and Implications for Seed Dispersal

Avian frugivores historically played important roles as seed dispersers across the Hawaiian Islands, but presently, the ‘Ōma‘o ( Myadestes obscurus ) is the only extant native frugivore in the wild on the Island of Hawaii. During recent decades, the introduced generalist Japanese White‐eye ( Zosterops japonicus ) has become the most common bird in Hawaii. The movements of avian frugivores largely dictate how far seeds get dispersed and into what kinds of microhabitats. This study compares the movement patterns and diet of the ‘Ōma‘o to the Japanese White‐eye to understand how a native differs from a non‐native frugivore in the type and distances of seeds dispersed. Radiotelemetry was conducted on nine ‘Ōma‘o and nine Japanese White‐eyes in a system of natural forest fragments ( kīpuka ) created by lava flows. Japanese White‐eyes disperse seeds approximately twice as far as ‘Ōma‘o; during the time of gut passage, ‘Ōma‘o move a mean distance of 98.1 m, and Japanese White‐eyes move 170.1–194.8 m. However, the ‘Ōma‘o disperses the seeds of at least seven different native fruit species compared with two dispersed by Japanese White‐eyes. Japanese White‐eyes were found to disperse seeds smaller than 1.5 mm, whereas the ‘Ōma‘o dispersed seeds up to 6 mm in diameter. Despite their ecological differences, both birds distribute certain seeds within and among kīpuka and likely facilitate primary succession of fruiting plants in the young lava matrix. However, this study suggests that if the ‘Ōma‘o were extirpated, a smaller‐bodied generalist cannot entirely substitute for the ecological role played by the native frugivore.