This small green passerine, introduced from Japan to the Hawaiian Islands in 1929, spread quickly to all the main islands and successfully invaded forests from sea level to the highest reaches of the mountains, rapidly becoming the most abundant and widespread passerine in the archipelago. White-eyes are commonly observed throughout the islands in both urban and pristine native habitats, in small flocks gleaning insects or gathering fruit and nectar from shrubs and understory subcanopy vegetation. Large flocks form during the nonbreeding period from late summer to January or February. Pairs breed from at least January to August, with the first eggs in February.
Controversy surrounds the Japanese White-eye because it has spread and increased while many native Hawaiian birds have declined; some see cause and effect here, but convincing data are lacking. Since Berger ( Berger 1981 ) summarized our knowledge of this species, there have been few comprehensive studies of the Japanese White-eye in the Hawaiian Islands, although several projects have examined specific aspects of its biology: possible competition with native birds, food preferences and seed dispersal, distribution, and disease. More in-depth studies will be necessary before we completely understand the comprehensive dynamics and integration of white-eyes into Hawaiian ecosystems.