Japanese White-eye
Encyclopedia
The Japanese White-eye also known as the mejiro (メジロ, 目白), is a small passerine
Passerine
A passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders: with over 5,000 identified species, it has roughly...

 bird in the white-eye
White-eye
White-eye can refer to:*White-eye , a large family of birds.*White-eye , a species of fish.*White-eye mutation, a mutation in Drosophila melanogaster linked to the X chromosome, found by reciprocal cross breeding experiments in 1906.*A lioness member of the Marsh Pride of lions that have featured...

 family. The specific epithet is occasionally written japonica, but this is incorrect due to the gender of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

. Its native range includes much of east Asia, including Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

, Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...

, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

, and the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

. It has been intentionally introduced
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...

 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.

Introduced to Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

 in 1929 as a means of insect control, it has since become a common bird on the Hawaiian Islands, and has become a vector for avian parasites that are now known to adversely affect populations of native birds such as Hawaiian honeycreeper
Hawaiian honeycreeper
Hawaiian honeycreepers are small, passerine birds endemic to Hawaii. Some authorities still categorize this group as a family Drepanididae, but in recent years, most authorities consider them a subfamily, Drepanidinae, of Fringillidae, the finch family...

s, as well as spreading invasive plant species through discarded seeds http://www.earlham.edu/~biol/hawaii/birds.htm.

Description

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.

Behavior

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
Interspecific
Interspecific is a term used in biology to describe behaviors, biochemical variations and other issues between individuals of separate species, thereby contrasting with intraspecific...

 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
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...

 at any one time.

Social hierarchy in a flock is established through physical displays. Some of these displays are not sex dependent, such as wing flicks exposing the underwing, wing flutters and vibrations, as well as open beak displays and beak snaps (rapid shutting of the beak to make a snapping noise). During breeding seasons, however, males establish territories via the sex-specific activity of singing loudly. Males will fend off intruders of the same species, yet will allow other species of birds to nest inside of their territory.

Nesting

Pairs of individuals, generally monogamous, choose a location for the nest between 1 and 30 meters above ground level. Construction of the nest lasts 7-10 days on average, and a variety of nesting material may be used (living and non-living); spider webs, moss, lichens, and mammal hair are all examples of building media that the birds employ. When building nests, they often steal material from the nests of other birds. Nests tend to be cup shaped, with a diameter of 56.2 mm and a depth of 41.7 mm. The majority of nests are only used once, but some may be used up to three times in any given season.

Feeding

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.

Distribution

The Japanese White-eye is naturally found in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

, eastern China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

, and the northern Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

. Migratory
Bird migration
Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...

 populations of the bird spend winters in Burma, Hainan Island, and Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...

. The White-eye is widespread and common in Japan, considered one of the more dominant bird species.

The Japanese White-eye, originally introduced in O’ahu
Oahu
Oahu or Oahu , known as "The Gathering Place", is the third largest of the Hawaiian Islands and most populous of the islands in the U.S. state of Hawaii. The state capital Honolulu is located on the southeast coast...

 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.

Predators

Organisms known to prey upon native Hawaiian avian species include small mammals, like the Polynesian
Polynesian Rat
The Polynesian Rat, or Pacific Rat , known to the Māori as kiore, is the third most widespread species of rat in the world behind the Brown Rat and Black Rat. The Polynesian Rat originates in Southeast Asia but, like its cousins, has become well travelled – infiltrating Fiji and most Polynesian...

, black
Black Rat
The black rat is a common long-tailed rodent of the genus Rattus in the subfamily Murinae . The species originated in tropical Asia and spread through the Near East in Roman times before reaching Europe by the 1st century and spreading with Europeans across the world.-Taxonomy:The black rat was...

, and Norway rats, and the mongoose
Mongoose
Mongoose are a family of 33 living species of small carnivorans from southern Eurasia and mainland Africa. Four additional species from Madagascar in the subfamily Galidiinae, which were previously classified in this family, are also referred to as "mongooses" or "mongoose-like"...

. There are no documented predators of the Japanese white-eye. It can only be inferred that organisms that prey on small mammals and birds in the same area as the Japanese White-eye also prey on the White-eye itself.

Competitors

In its natural habitat, the Japanese White-eye competes with other native passerine bird species, including those of the same genus, such as the Bonin White-eye
Bonin White-eye
The Bonin White-eye Apalopteron familiare or is a small yellow and grey bird endemic to the Ogasawara Islands of Japan. Until recently it was considered part of the Meliphagidae family of honeyeaters and was called the Bonin Honeyeater.A distinctive feature of the bird is the white rim around the...

 (Apalopteron familiare). In Hawaii, the Japanese White-eye competes with native passerines such as the Common 'Amakihi, for food (such as nectar and fruit), as well as for space. In Hawaii, the Japanese White-eye has been observed visiting endemic (native) floral species thought to have coevolved with endemic nectarivorous avian species (those that eat nectar). This means that, over time, changes in native flowers have triggered changes in native birds that feed on the nectar of these flowers; the latter change then triggers another change in the flowers, and the whole process continues to repeat itself. The visitation of the White-eye, along with the disappearance of those endemic nectarivorous passerine bird species, suggests that the White-eye is out-competing those endemic species for the floral resource (nectar).

Effects on Native Hawaiian Birds

The Japanese White-eye’s successful invasion of the Hawaiian Islands can be partially attributed to the lack of coevolution between endemic species and the White-eye. The occurrence of coevolution is driven by species interactions that directly impact physical development. In many cases coevolution is derived from competition in which both species vie for an edge or advantage to maximize their dietary or “resource” acquirement. Because the White-eye did not coevolve with avian species native to Hawaii, the White-eye has certain advantageous characteristics, such as the resistance to avian malaria
Avian malaria
Avian malaria is a parasitic disease of birds.-Etiology:Avian malaria is most notably caused by Plasmodium relictum, a protist that infects birds in tropical regions...

, that the native species do not possess. The native species never had a chance to change in response to evolutionary changes in the White-eye.

White-eye range expansion has also been cited as a negative effect on native bird species. White-eye expansion is arguably characteristic of what E.O Wilson called a “Taxon
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

 Cycle”. The cycle attempts to model the interactions between endemic species and newly immigrated non-native populations through the use of “Stages” –each with defined characteristics with respect to overall population behavior. A newly immigrated species (Stage 1) is expected to experience rapid growth through the new habitat largely due to the lack of effective endemic (Stage 3) persistence – the ability of the community to repel outside forces that may cause changes in its species composition. This prediction matches much of the current data indicating that the White-eye has become highly common on most if not all of the Hawaiian Islands. The force of natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

 has promoted the dietary or “resource” specialization of many of the later stage endemic species – a prime example being the honeycreeper
Hawaiian honeycreeper
Hawaiian honeycreepers are small, passerine birds endemic to Hawaii. Some authorities still categorize this group as a family Drepanididae, but in recent years, most authorities consider them a subfamily, Drepanidinae, of Fringillidae, the finch family...

. This particular species has become especially affected by the White-eye presence due to honeycreeper dependence on nectar as a primary resource. In contrast the White-eye maintains a highly diverse selection of dietary options (including nectar) and is able to take full advantage of numerous habitats on the islands. The differences in resource limitations between the two species has resulted in the drastic decline of the honeycreeper population, as they are out competed by the invasive White-eye. This occurrence is best explained by the Competitive Exclusion Principle
Competitive exclusion principle
In ecology, the competitive exclusion principle, sometimes referred to as Gause's law of competitive exclusion or just Gause's law, is a proposition which states that two species competing for the same resources cannot coexist if other ecological factors are constant...

, which dictates that two complete competitors cannot co-exist.

Increases in the Japanese White-eye population in Hawaii have negative effects on the growth and survival of native birds in the community. In one study, the bill length, tarsus
Tarsus
Tarsus may refer to:*Tarsus , a cluster of articulating bones in each foot** Tarsometatarsus, a fusion of the tarsus and metatarsus mainly found in birds...

 length, and mass of native Hawaiian passerine birds were measured during 1987-2006 using the technique of mark and recapture
Mark and recapture
Mark and recapture is a method commonly used in ecology to estimate population size. This method is most valuable when a researcher fails to detect all individuals present within a population of interest every time that researcher visits the study area...

. In 2000, juveniles
Juveniles
Juvenile may refer to:* Juvenile * Minor * Children's literature* Children's clothing...

 (not-yet-adults) of every native species showed lower mass and shorter bills than before. These changes led to decreased juvenile survival and decreased survival of second year individuals/older adults, respectively. These birds also showed shorter tarsi, the group of bones in the hind feet of some vertebrates; although this change was less drastic than that seen with the bills. Birds with original bill lengths closest to that of the White-eye suffered the most, undergoing changes that lowered their foraging efficiency. For example, the endangered Hawaiian akepa was viable during 1987-1999 but not during 2000-2006, associated with an abrupt increase in White-eyes. These facts document strong community-wide exploitative competition for food between the Japanese White-eye and passerine birds native to Hawaii, meaning that the White-eye depletes the availability of food for other bird species. They also compete for space; the White-eye has expanded its range into remote areas within the last two decades: 1980-2000. The distribution of the Japanese White-eye has been shown to negatively correlate with the distributions of native birds, meaning that as the white-eye becomes more highly distributed, native birds become less distributed. Many Hawaiian birds are endangered or already extinct; this occurrence is believed to be related to the invasion of the White-eye.

Effects on Hawaiian Plants

Because many of the Hawaiian birds that have gone extinct acted as pollinators, there is a concern about the survival of certain plant species, such as the Hawaiian Lobelioideae. The Japanese White-eye has been pinned as a possible replacement pollinator. Lobelioids that were pollinated by native birds that are now extinct may benefit from the presence of the White-eye, but more detailed studies are needed to determine the degree of pollen transfer affected by White-eyes. Also, this replacement could lead to differing levels of outcrossing
Outcrossing
Outcrossing is the practice of introducing unrelated genetic material into a breeding line. It increases genetic diversity, thus reducing the probability of all individuals being subject to disease or reducing genetic abnormalities...

 compared to those resulting from visits by the native species of birds. Outcrossing is the introduction of unrelated genetic material into a breeding line. Therefore, White-eye pollination may prove to be beneficial, as outcrossing increases genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....

, thus reducing the probability of all individuals being subject to disease; increasing genetic diversity also reduces genetic abnormalities. Again, a more detailed study is needed to determine the potential benefits of White-eye pollination.

A similar trend to that of Hawaii’s was seen when the bird was introduced to the Bonin Islands of Japan; while native to the country, the White-eye was not originally present on these islands. As in Hawaii, the study conducted in the Bonin Islands suggests that the Japanese White-eye may be taking over the actions of native birds in relation to plants present on the islands. Unlike Hawaii (in which this action was pollination), the action taken over by the White-eye in the Bonin Islands is seed-dispersal; this dispersal was previously carried out by native birds – whether still present or already extinct. The White-eye has not been cited as taking over seed-dispersal in Hawaii because they rarely ingest the seeds of Hawaiian plants, such as the Firetree
Myrica faya
Myrica faya is a species of Myrica, native to Macaronesia , and possibly also southern Portugal....

. For this reason, they cannot disperse the seeds over great distances, making them poor seed dispersers. While the actions of the White-eye on the Hawaiian and Bonin Islands are indeed different, they are both significant. This is because islands themselves are particularly vulnerable to the drastic effects of introduced competitors, predators, and diseases, because these communities have evolved in their absence.

Conservation

Native species need normal juvenile mass and bill length to recover/persist, but in order for this to happen, food must be restored to former levels. There is support that an introduced bird, such as the Japanese White-eye, is responsible for the food shortage. Control of the White-eye is therefore essential for the recovery of native Hawaiian birds. The determination of the status of native birds is essential; those found to be endangered could possibly benefit from the designation of critical habitat. In 1980, a program to eradicate (eliminate) the Indian White-eye in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 involved mist-netting
Mist net
Mist nets are used by ornithologists and bat biologists to capture wild birds and bats for banding or other research projects. Mist nets are typically made of nylon mesh suspended between two poles, resembling an oversized volleyball net. When properly deployed, the nets are virtually invisible...

and shooting the birds, and this proved to be the most successful of the various capture methods explored. Whether eradication is feasible and applicable to other instances of invasive exotic birds is yet to be determined, but could be considered a possibility for the eradication of the Japanese White-eye in the Hawaiian Islands. However, because the White-eye’s current ecological role is not fully understood (i.e. seed disperser, pollinator, etc.) further studies are necessary before any drastic measures are taken.

External links

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