The Japanese white-eye (Zosterops japonicus), also known as the mejiro is a small passerine bird in the white-eye family. Its native range includes much of east Asia, including Japan, Korea, China, Vietnam, Taiwan, and the Philippines. It has been intentionally introduced to other parts of the world as a pet and as pest control, with mixed results. As one of the native species of the Japanese islands, it has been depicted in Japanese art on numerous occasions, and historically was kept as a cage bird.
The Japanese white-eye is olive green on its back, from anterior to posterior, and is pale green on its underside. Its feet, legs, and bill range from black to brown. It has a green forehead and a yellow throat. The white-eye has rounded wings and a long, slender bill – both of which indicate this bird to be very acrobatic. Its wings are dark brown, but outlined in green. Like other white-eyes, this species exhibits the distinctive white eyering that gives it its name (mejiro also meaning "white eye" in Japanese). Adults range from 4 to 4.5 inches in length, and weigh between 9.75 and 12.75 grams.
This bird species is rarely found on the ground. It is a very sociable species that may form flocks with other species, in which the birds form groups to forage during flight; white-eyes only flock with birds of other species outside of the breeding season. Allopreening – the art of cleaning, grooming, and maintaining parts of the body – is extremely common. Interspecific allopreening (between different species) has been observed in captivity. While sociable, however, the white-eye typically forms monogamous relationships with mates – it has only one mate at any one time.
The species is omnivorous, living on a diet of fruit from several species of flowering plants, various types of insects, and nectar at all levels of foliage. It feeds on insects by searching the leaves of flowers and scouring tree bark for larvae. Consequences of its diet include regulation of local insect populations and dispersal of seeds; however, the white-eye's seed-dispersal ability does not seem to be significant in Hawaii.
The Japanese white-eye, originally introduced in O’ahu in 1929, has rapidly expanded its population and can now be found on every island of Hawaii; the climates of these islands range from tropical rain forests to deciduous forests. After subsequent releases and natural range expansion (enlargement of the area it occupies), the white-eye was determined to be the most abundant land bird on the Hawaiian Islands as early as 1987. It has become a vector for avian parasites that are now known to adversely affect populations of native birds such as Hawaiian honeycreepers, as well as spreading invasive plant species through discarded seeds.