Golden White-eye
Encyclopedia
The Golden White-eye is a species of bird
in the white-eye family Zosteropidae
. It is the only species within the genus Cleptornis. The Golden White-eye was once considered to be a honeyeater
in the family Meliphagidae and although it is now known to be a white-eye, its position within that family is still uncertain. The species is restricted to the islands of Saipan
and Aguijan
in the Northern Mariana Islands
, where it is sympatric (shares its range) and competes with the related Bridled White-eye
. The Golden White-eye has golden plumage
and a pale eye-ring. It feeds on insects, fruit, and nectar and forages in pairs or small family groups. The bird is monogamous and lays two eggs in a small cup nest.
Fossil evidence shows the Golden White-eye once also occurred on Tinian
and Rota
but was extirpated
in those locations through the impact of human activities. Despite its current abundance on Saipan and Aguijan, and the fact that it has among the highest recorded densities for any bird, it is nevertheless considered to be critically endangered
. It is threatened by the invasive
Brown Tree Snake
, which has recently become established
on Saipan, and this predator is expected to cause a rapid decline in the population if not controlled. Efforts are under way to control the snakes and breed
the white-eye in zoo
s.
(Meliphagidae). It was placed with the genus Ptilotis by French naturalist Émile Oustalet
when he described the species in 1889 (that genus is now considered defunct and is no longer used). It was subsequently moved to the genus Cleptornis, which had been provisionally established by Oustalet in case the species proved to be distinct. Behavioural and morphological characteristics led American ornithologist Harold Douglas Pratt, Jr.
, to suggest in 1987 that it was related to the white-eye
s. Subsequent studies have supported the idea that this species was a white-eye. It is possibly most closely related to the Micronesia
n white-eyes of the genus Rukia
, or the monotypic Bonin White-eye
(Apalopteron), another species once placed with the honeyeaters and subsequently moved to the white-eyes. The Golden White-eye has a long 10th primary
(one of the flight feathers), unlike other white-eyes where that primary is reduced or absent, which has led to the alternative suggestion that it is basal
(an early offshoot) among the white-eyes.
Its generic name, Cleptornis, is derived from the Ancient Greek
kleptes, a robber or thief, and ornis, a bird. This does not reference any aspect of the Golden White-eye's behaviour, but the old French
name of the Mariana Islands, les Îles des Voleurs, or Robbers' Islands. The specific epithet marchei refers to the French explorer and writer Antoine-Alfred Marche
, who procured the original specimens.
The Golden White-eye is endemic to the Northern Mariana Islands
in the western Pacific Ocean, where it currently occurs on the islands of Saipan
and Aguijan
. Within its range, it occupies a variety of habitat
s, both natural and man-made. It is common in native forest
s, particularly limestone
forests, but also occurs in open shrubland
and suburban area
s. On Saipan, the only habitats it is absent from are the marshes around Lake Susupe and grassy savanna
s.
(0.7 oz
). The species has bright, unmistakable plumage
, with: an orange-yellow head coupled with a pale eye-ring; a yellow-green back, wings, and tail; and golden orange undersides. The bill and legs are also orange. The plumage of both sexes is similar; the males can be told from the females only when examined in the hand, since the males have longer wings than the females. The juveniles have similar plumage, though duller than the adults', with brownish patches on the face and neck and brown-yellow streaks on the breast. Juveniles also have dusky bills and dull legs.
The Golden White-eye makes a variety of calls. The song is a long raspy warble, rendered as "séé mé-can you séé mé-I can séé yóú-can you séé mé". The species also makes rasping shorter calls and whistles when in flocks and in flight. Chicks give plaintive whistles when begging for food from adults.
, which forages in groups and is not territorial, the Golden White-eye occurs in pairs or small family groups consisting of a breeding pair and fledged young. The Golden White-eye is also territorial
, and pairs will sing throughout the day in response to neighbouring pairs. Groups can become aggressive when they encounter one another. The Golden White-eye is also aggressive towards the smaller Bridled White-eye, chasing it away from food and perches and flying through flocks of them in order to disperse them. While it chases other forest passerine
s, it is less aggressive towards them, and in fact the Rufous Fantail
seeks out the Golden White-eye, foraging behind it to snatch insects flushed by the latter species. The Golden White-eye is socially dominant over the Bridled White-eyes and Rufous Fantails, but it is subordinate to the Micronesian Myzomela
and is chased by that species. It is also occasionally chased by the fantails if it approaches their nests too closely.
The Golden White-eye is a generalist, feeding on fruit, berries, and insects. Nectar forms part of the diet, and, along with the Micronesian Myzomela
and the Bridled White-eye
, the Golden White-eye is a pollinator of some trees, albeit not one as important as these other species. Insects may be either gleaned
from the bark of trees and from leaves, or caught in the air. Certain tree species are preferred as foraging habitat. The common forest tree Cynometra ramifolia
is the most favoured tree and used more frequently than the equally common Guamia mariannae
. There is considerable overlap between this species' foraging range and that of the Bridled White-eye
, but the Golden White-eye is more generalised in its diet. Within the forest there is some partitioning of niche, with Bridled White-eyes (and Micronesian Myzomelas) feeding primarily in the forest canopy, and the Golden White-eye feeding in both the canopy and understory
of the forest, as well as a variety of smaller trees and bushes. It shares the understory with the Rufous Fantail, which has a different feeding technique. At a smaller scale additional partitioning occurs. The Golden White-eye shows differences in the preferred microhabitat for obtaining insects, for example, feeding in dead leaves and branches, whereas the Bridled White-eye prefers gleaning insects on live leaves. It is the most generalised of all the extant forest passerines on Saipan. It has been suggested that the versatility in diet and foraging technique is an adaptation to the challenges presented by typhoons
, which can dramatically alter the structure of the forest.
. The nests
are simple undecorated cups of casuarina
needles, grasses, and vines. These are placed around 2.9 m (between 1.5 and 6.5 m) off the ground in a variety of trees including Casuarina, Guamia, Cynometra, Leucaena
, and Citrus
. The nests are predated
by other bird species, specifically Micronesian Starling
s and Collared Kingfisher
s. In addition, the introduced
Green Tree Skink has also been seen predating the nests.
The typical clutch size
is two eggs, 20.3 × 15.1 mm in size, which are pale blueish green with red or brown splotches that are concentrated around the wider end. Both sexes share the incubation duties
, with each parent incubating for stints of around 25 minutes before being relieved. This species is extremely territorial around the nest, chasing away other birds, including Brindled White-eyes, Rufous Fantails, and other Golden White-eyes. From laying it takes about two weeks for the eggs to hatch. The hatchlings are altricial
, in other words naked and helpless. Both parents share the brooding and feeding duties, and take away faecal
sacks to keep the nest clean. The diet of the chicks is almost exclusively composed of insects and caterpillars. Chicks fledge
around 10–14 days after hatching. After fledging they may remain with their parents in small groups for some time.
The range of the Golden White-eye has contracted considerably since the arrival of humans in the Mariana Islands. Fossil
bones of this species have been found on the nearby islands of Tinian
and Rota
, and it may once have occurred on Guam
and other islands in the Marianas.
At present the Golden White-eye is very common, and in fact a 1996 study found that their densities on Saipan were among the highest recorded for any bird, up to 2,095 birds/km² (8.47 per acre). It was believed that Saipan cannot sustain a larger population of this white-eye than it already does. A 2009 study, which incorporated results from a 2007 survey, found that the species had declined between 1982 and 2007, in common with two other species on Saipan, the Rufous Fantail and the Nightingale Reed-warbler
. All three species are insectivorous and were theorised to have declined due to habitat loss. Nevertheless the species remained relatively abundant, and the current world population is estimated at around 71,997 birds.
The species is nonetheless evaluated as critically endangered
by the IUCN because the population is expected to undergo a rapid decline. The primary threat to this species is the Brown Tree Snake
, a native of Australia
, New Guinea
and the Solomon Islands
, which eliminated all 12 landbird species on nearby Guam after being accidentally introduced
. The snake recently arrived on Saipan, one of the two islands that compose the range of the Golden White-eye, and which holds the largest population of the species. The isolation of Aguijan makes the introduction of brown tree snakes there unlikely, but the small population there is vulnerable as the island is only 718 ha
(1774 acres) in size and a direct hit by a supertyphoon
could wipe them out. Efforts are under way to breed the species in captivity
and to control the snakes on Saipan. Six zoos have recently received this species and breeding was expected to begin by 2011. Success came more quickly, and the first captive birds were bred in 2009 in the North Carolina Zoo
. Birds from captive breeding will be introduced on new islands. In addition, translocations
of 50 birds from Saipan to the island of Sarigan
, a predator-free island reserve, are currently being planned by scientists working to save the species.
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
in the white-eye family Zosteropidae
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...
. It is the only species within the genus Cleptornis. The Golden White-eye was once considered to be a honeyeater
Honeyeater
The honeyeaters are a large and diverse family of small to medium sized birds most common in Australia and New Guinea, but also found in New Zealand, the Pacific islands as far east as Samoa and Tonga, and the islands to the north and west of New Guinea known as Wallacea...
in the family Meliphagidae and although it is now known to be a white-eye, its position within that family is still uncertain. The species is restricted to the islands of Saipan
Saipan
Saipan is the largest island of the United States Commonwealth of the Northern Mariana Islands , a chain of 15 tropical islands belonging to the Marianas archipelago in the western Pacific Ocean with a total area of . The 2000 census population was 62,392...
and Aguijan
Aguijan
Aguijan is a small bean-shaped coralline island in the Northern Mariana Islands chain situated southwest of Tinian, from which it is separated by the Tinian Channel. It is only 7.09 km² in size and is nicknamed Goat Island due to the large number of feral goats present there...
in the Northern Mariana Islands
Northern Mariana Islands
The Northern Mariana Islands, officially the Commonwealth of the Northern Mariana Islands , is a commonwealth in political union with the United States, occupying a strategic region of the western Pacific Ocean. It consists of 15 islands about three-quarters of the way from Hawaii to the Philippines...
, where it is sympatric (shares its range) and competes with the related Bridled White-eye
Bridled White-eye
The Bridled White-eye is a species of bird in the Zosteropidae family.It is endemic to the Mariana Islands, where it is today restricted to the islands of Tinian, Saipan and Aguijan in the Northern Mariana Islands...
. The Golden White-eye has golden plumage
Plumage
Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...
and a pale eye-ring. It feeds on insects, fruit, and nectar and forages in pairs or small family groups. The bird is monogamous and lays two eggs in a small cup nest.
Fossil evidence shows the Golden White-eye once also occurred on Tinian
Tinian
Tinian is one of the three principal islands of the Commonwealth of the Northern Mariana Islands.-Geography:Tinian is about 5 miles southwest of its sister island, Saipan, from which it is separated by the Saipan Channel. It has a land area of 39 sq.mi....
and Rota
Rota (island)
Rota also known as the "peaceful island", is the southernmost island of the United States Commonwealth of the Northern Mariana Islands and the second southernmost of the Marianas Archipelago. It lies approximately 40 miles north-northeast of the United States territory of Guam...
but was extirpated
Local extinction
Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...
in those locations through the impact of human activities. Despite its current abundance on Saipan and Aguijan, and the fact that it has among the highest recorded densities for any bird, it is nevertheless considered to be critically endangered
Critically endangered
Version 2010.3 of the IUCN Red List of Threatened Species identified 3744 Critically Endangered species, subspecies and varieties, stocks and subpopulations.Critically Endangered by kingdom:*1993 Animalia*2 Fungi*1745 Plantae*4 Protista-References:...
. It is threatened by the invasive
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
Brown Tree Snake
Brown tree snake
The brown tree snake is an arboreal rear-fanged colubrid snake native to eastern and northern coastal Australia, Papua New Guinea, and a large number of islands in northwestern Melanesia....
, which has recently become established
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...
on Saipan, and this predator is expected to cause a rapid decline in the population if not controlled. Efforts are under way to control the snakes and breed
Captive breeding
Captive breedingis the process of breeding animals in human controlled environments with restricted settings, such as wildlife reserves, zoos and other conservation facilities; sometimes the process is construed to include release of individual organisms to the wild, when there is sufficient...
the white-eye in zoo
Zoo
A zoological garden, zoological park, menagerie, or zoo is a facility in which animals are confined within enclosures, displayed to the public, and in which they may also be bred....
s.
Taxonomy
The species was once called the Golden Honeyeater as it was considered to be a honeyeaterHoneyeater
The honeyeaters are a large and diverse family of small to medium sized birds most common in Australia and New Guinea, but also found in New Zealand, the Pacific islands as far east as Samoa and Tonga, and the islands to the north and west of New Guinea known as Wallacea...
(Meliphagidae). It was placed with the genus Ptilotis by French naturalist Émile Oustalet
Émile Oustalet
Jean-Frédéric Émile Oustalet was a French zoologist.Oustalet was born at Montbéliard, in the department of Doubs. He studied at the Ecole des Hautes-Etudes and his first scientific work was on the respiratory organs of dragonfly larvae...
when he described the species in 1889 (that genus is now considered defunct and is no longer used). It was subsequently moved to the genus Cleptornis, which had been provisionally established by Oustalet in case the species proved to be distinct. Behavioural and morphological characteristics led American ornithologist Harold Douglas Pratt, Jr.
Harold Douglas Pratt, Jr.
Harold Douglas Pratt, Jr. , often credited in the short form H. Douglas Pratt, is an American ornithologist, bio acoustican, wildlife photographer and bird illustrator. His main research field are the endemic avifaunas of Hawaii and other islands in the Pacific where he was one of the pioneers of...
, to suggest in 1987 that it was related to 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...
s. Subsequent studies have supported the idea that this species was a white-eye. It is possibly most closely related to the Micronesia
Micronesia
Micronesia is a subregion of Oceania, comprising thousands of small islands in the western Pacific Ocean. It is distinct from Melanesia to the south, and Polynesia to the east. The Philippines lie to the west, and Indonesia to the southwest....
n white-eyes of the genus Rukia
Rukia (bird)
Rukia is a small genus of birds in the white-eye family. Its two members are found in the Federated States of Micronesia on the island of Pohnpei and the Faichuk group of the Chuuk islands...
, or the monotypic 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), another species once placed with the honeyeaters and subsequently moved to the white-eyes. The Golden White-eye has a long 10th primary
Flight feather
Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings or tail of a bird; those on the wings are called remiges while those on the tail are called rectrices . Their primary function is to aid in the generation of both thrust and lift, thereby...
(one of the flight feathers), unlike other white-eyes where that primary is reduced or absent, which has led to the alternative suggestion that it is basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
(an early offshoot) among the white-eyes.
Its generic name, Cleptornis, is derived from the Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
kleptes, a robber or thief, and ornis, a bird. This does not reference any aspect of the Golden White-eye's behaviour, but the old French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
name of the Mariana Islands, les Îles des Voleurs, or Robbers' Islands. The specific epithet marchei refers to the French explorer and writer Antoine-Alfred Marche
Antoine-Alfred Marche
Antoine-Alfred Marche was a French naturalist and explorer. He visited Africa, the Philippines and finally the Marianas Islands. He made collections of various artifacts...
, who procured the original specimens.
Distribution and habitat
Northern Mariana Islands
The Northern Mariana Islands, officially the Commonwealth of the Northern Mariana Islands , is a commonwealth in political union with the United States, occupying a strategic region of the western Pacific Ocean. It consists of 15 islands about three-quarters of the way from Hawaii to the Philippines...
in the western Pacific Ocean, where it currently occurs on the islands of Saipan
Saipan
Saipan is the largest island of the United States Commonwealth of the Northern Mariana Islands , a chain of 15 tropical islands belonging to the Marianas archipelago in the western Pacific Ocean with a total area of . The 2000 census population was 62,392...
and Aguijan
Aguijan
Aguijan is a small bean-shaped coralline island in the Northern Mariana Islands chain situated southwest of Tinian, from which it is separated by the Tinian Channel. It is only 7.09 km² in size and is nicknamed Goat Island due to the large number of feral goats present there...
. Within its range, it occupies a variety of habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s, both natural and man-made. It is common in native forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
s, particularly limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
forests, but also occurs in open shrubland
Shrubland
Shrubland, scrubland, scrub or brush is a plant community characterized by vegetation dominated by shrubs, often also including grasses, herbs, and geophytes. Shrubland may either occur naturally or be the result of human activity...
and suburban area
Suburb
The word suburb mostly refers to a residential area, either existing as part of a city or as a separate residential community within commuting distance of a city . Some suburbs have a degree of administrative autonomy, and most have lower population density than inner city neighborhoods...
s. On Saipan, the only habitats it is absent from are the marshes around Lake Susupe and grassy savanna
Savanna
A savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of C4 grasses.Some...
s.
Description
The Golden White-eye differs from the other white-eyes in having large eyes and an outermost primary wing feather that is not reduced (as it is in the other species). It is a large white-eye, 14 cm (5.5 in) long and weighing around 20 gGram
The gram is a metric system unit of mass....
(0.7 oz
Ounce
The ounce is a unit of mass with several definitions, the most commonly used of which are equal to approximately 28 grams. The ounce is used in a number of different systems, including various systems of mass that form part of the imperial and United States customary systems...
). The species has bright, unmistakable plumage
Plumage
Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...
, with: an orange-yellow head coupled with a pale eye-ring; a yellow-green back, wings, and tail; and golden orange undersides. The bill and legs are also orange. The plumage of both sexes is similar; the males can be told from the females only when examined in the hand, since the males have longer wings than the females. The juveniles have similar plumage, though duller than the adults', with brownish patches on the face and neck and brown-yellow streaks on the breast. Juveniles also have dusky bills and dull legs.
The Golden White-eye makes a variety of calls. The song is a long raspy warble, rendered as "séé mé-can you séé mé-I can séé yóú-can you séé mé". The species also makes rasping shorter calls and whistles when in flocks and in flight. Chicks give plaintive whistles when begging for food from adults.
Behaviour
Like other white-eyes, the Golden White-eye is diurnal. In contrast to the Bridled White-eyeBridled White-eye
The Bridled White-eye is a species of bird in the Zosteropidae family.It is endemic to the Mariana Islands, where it is today restricted to the islands of Tinian, Saipan and Aguijan in the Northern Mariana Islands...
, which forages in groups and is not territorial, the Golden White-eye occurs in pairs or small family groups consisting of a breeding pair and fledged young. The Golden White-eye is also territorial
Territory (animal)
In ethology the term territory refers to any sociographical area that an animal of a particular species consistently defends against conspecifics...
, and pairs will sing throughout the day in response to neighbouring pairs. Groups can become aggressive when they encounter one another. The Golden White-eye is also aggressive towards the smaller Bridled White-eye, chasing it away from food and perches and flying through flocks of them in order to disperse them. While it chases other forest 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...
s, it is less aggressive towards them, and in fact the Rufous Fantail
Rufous Fantail
The Rufous Fantail Rhipidura rufifrons inhabits the east coast of Australia. The base of its tail is bright orange-red in colour and their wings are greyish brown. They have a black and white breast that grades into a white colour on the chin and throat....
seeks out the Golden White-eye, foraging behind it to snatch insects flushed by the latter species. The Golden White-eye is socially dominant over the Bridled White-eyes and Rufous Fantails, but it is subordinate to the Micronesian Myzomela
Micronesian Myzomela
The Micronesian Myzomela is a species of bird in the honeyeater family Meliphagidae. The species forms a superspeices wit a number of related and similar looking island and mainland myzomelas across the Pacific and Australasia...
and is chased by that species. It is also occasionally chased by the fantails if it approaches their nests too closely.
Diet and feeding
Micronesian Myzomela
The Micronesian Myzomela is a species of bird in the honeyeater family Meliphagidae. The species forms a superspeices wit a number of related and similar looking island and mainland myzomelas across the Pacific and Australasia...
and the Bridled White-eye
Bridled White-eye
The Bridled White-eye is a species of bird in the Zosteropidae family.It is endemic to the Mariana Islands, where it is today restricted to the islands of Tinian, Saipan and Aguijan in the Northern Mariana Islands...
, the Golden White-eye is a pollinator of some trees, albeit not one as important as these other species. Insects may be either gleaned
Gleaning (birds)
Gleaning is a term for a feeding strategy by birds in which they catch invertebrate prey, mainly arthropods, by plucking them from foliage or the ground, from crevices such as rock faces and under the eaves of houses, or even, as in the case of ticks and lice, from living animals. This behavior is...
from the bark of trees and from leaves, or caught in the air. Certain tree species are preferred as foraging habitat. The common forest tree Cynometra ramifolia
Cynometra
Cynometra is genus of tropical forest trees with a pantropical distribution. It is particularly important as a forest component in west Africa and the neotropics. Cynometra alexandri is a familiar timber tree of central and east Africa...
is the most favoured tree and used more frequently than the equally common Guamia mariannae
Guamia
Guamia is a monotypic genus of flowering plants in the soursop family, Annonaceae. The sole species it contains, Guamia mariannae, is endemic to the Marianas Islands.-External links:...
. There is considerable overlap between this species' foraging range and that of the Bridled White-eye
Bridled White-eye
The Bridled White-eye is a species of bird in the Zosteropidae family.It is endemic to the Mariana Islands, where it is today restricted to the islands of Tinian, Saipan and Aguijan in the Northern Mariana Islands...
, but the Golden White-eye is more generalised in its diet. Within the forest there is some partitioning of niche, with Bridled White-eyes (and Micronesian Myzomelas) feeding primarily in the forest canopy, and the Golden White-eye feeding in both the canopy and understory
Understory
Understory is the term for the area of a forest which grows at the lowest height level below the forest canopy. Plants in the understory consist of a mixture of seedlings and saplings of canopy trees together with understory shrubs and herbs...
of the forest, as well as a variety of smaller trees and bushes. It shares the understory with the Rufous Fantail, which has a different feeding technique. At a smaller scale additional partitioning occurs. The Golden White-eye shows differences in the preferred microhabitat for obtaining insects, for example, feeding in dead leaves and branches, whereas the Bridled White-eye prefers gleaning insects on live leaves. It is the most generalised of all the extant forest passerines on Saipan. It has been suggested that the versatility in diet and foraging technique is an adaptation to the challenges presented by typhoons
Pacific typhoon
A typhoon is a mature tropical cyclone that develops in the northwestern part of the Pacific Ocean between 180° and 100°E. This region is referred to as the northwest Pacific basin. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern , central , and...
, which can dramatically alter the structure of the forest.
Breeding
Breeding occurs throughout the year on Saipan, where the species' nesting behaviour has been studied. The peak breeding period seems to be from March to July. The species is monogamousMonogamy
Monogamy /Gr. μονός+γάμος - one+marriage/ a form of marriage in which an individual has only one spouse at any one time. In current usage monogamy often refers to having one sexual partner irrespective of marriage or reproduction...
. The nests
Bird nest
A bird nest is the spot in which a bird lays and incubates its eggs and raises its young. Although the term popularly refers to a specific structure made by the bird itself—such as the grassy cup nest of the American Robin or Eurasian Blackbird, or the elaborately woven hanging nest of the...
are simple undecorated cups of casuarina
Casuarina
Casuarina is a genus of 17 species in the family Casuarinaceae, native to Australasia, southeast Asia, and islands of the western Pacific Ocean. It was once treated as the sole genus in the family, but has been split into three genera .They are evergreen shrubs and trees growing to 35 m tall...
needles, grasses, and vines. These are placed around 2.9 m (between 1.5 and 6.5 m) off the ground in a variety of trees including Casuarina, Guamia, Cynometra, Leucaena
Leucaena
Leucaena is a genus of flowering plants in the subfamily Mimosoideae of the legume family Fabaceae. It contains about 24 species of trees and shrubs, which are commonly known as Leadtrees. They are native to the Americas, ranging from Texas in the United States south to Peru...
, and Citrus
Citrus
Citrus is a common term and genus of flowering plants in the rue family, Rutaceae. Citrus is believed to have originated in the part of Southeast Asia bordered by Northeastern India, Myanmar and the Yunnan province of China...
. The nests are predated
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
by other bird species, specifically Micronesian Starling
Micronesian Starling
The Micronesian Starling is a species of starling in the Sturnidae family.It is found in Micronesia, Northern Mariana Islands, and Palau....
s and Collared Kingfisher
Collared Kingfisher
The Collared Kingfisher is a medium-sized kingfisher belonging to the family Halcyonidae, the tree kingfishers. It is also known as the White-collared Kingfisher or Mangrove Kingfisher. It has a wide range extending from the Red Sea across southern Asia and Australasia to Polynesia...
s. In addition, the 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...
Green Tree Skink has also been seen predating the nests.
The typical clutch size
Clutch (eggs)
A clutch of eggs refers to all the eggs produced by birds or reptiles, often at a single time, particularly those laid in a nest.In birds, destruction of a clutch by predators, , results in double-clutching...
is two eggs, 20.3 × 15.1 mm in size, which are pale blueish green with red or brown splotches that are concentrated around the wider end. Both sexes share the incubation duties
Avian incubation
Incubation refers to the process by which certain oviparous animals hatch their eggs, and to the development of the embryo within the egg. The most vital factor of incubation is the constant temperature required for its development over a specific period. Especially in domestic fowl, the act of...
, with each parent incubating for stints of around 25 minutes before being relieved. This species is extremely territorial around the nest, chasing away other birds, including Brindled White-eyes, Rufous Fantails, and other Golden White-eyes. From laying it takes about two weeks for the eggs to hatch. The hatchlings are altricial
Altricial
Altricial, meaning "requiring nourishment", refers to a pattern of growth and development in organisms which are incapable of moving around on their own soon after hatching or being born...
, in other words naked and helpless. Both parents share the brooding and feeding duties, and take away faecal
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
sacks to keep the nest clean. The diet of the chicks is almost exclusively composed of insects and caterpillars. Chicks fledge
Fledge
Fledge is the stage in a young bird's life when the feathers and wing muscles are sufficiently developed for flight. It also describes the act of a chick's parents raising it to a fully grown state...
around 10–14 days after hatching. After fledging they may remain with their parents in small groups for some time.
Threats and conservation
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
bones of this species have been found on the nearby islands of Tinian
Tinian
Tinian is one of the three principal islands of the Commonwealth of the Northern Mariana Islands.-Geography:Tinian is about 5 miles southwest of its sister island, Saipan, from which it is separated by the Saipan Channel. It has a land area of 39 sq.mi....
and Rota
Rota (island)
Rota also known as the "peaceful island", is the southernmost island of the United States Commonwealth of the Northern Mariana Islands and the second southernmost of the Marianas Archipelago. It lies approximately 40 miles north-northeast of the United States territory of Guam...
, and it may once have occurred on Guam
Guam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...
and other islands in the Marianas.
At present the Golden White-eye is very common, and in fact a 1996 study found that their densities on Saipan were among the highest recorded for any bird, up to 2,095 birds/km² (8.47 per acre). It was believed that Saipan cannot sustain a larger population of this white-eye than it already does. A 2009 study, which incorporated results from a 2007 survey, found that the species had declined between 1982 and 2007, in common with two other species on Saipan, the Rufous Fantail and the Nightingale Reed-warbler
Nightingale Reed-warbler
The Nightingale Reed-warbler is a critically endangered songbird of the Mariana Islands. The Chamorro name for the bird is ga`ga` karisu ....
. All three species are insectivorous and were theorised to have declined due to habitat loss. Nevertheless the species remained relatively abundant, and the current world population is estimated at around 71,997 birds.
The species is nonetheless evaluated as critically endangered
Critically endangered
Version 2010.3 of the IUCN Red List of Threatened Species identified 3744 Critically Endangered species, subspecies and varieties, stocks and subpopulations.Critically Endangered by kingdom:*1993 Animalia*2 Fungi*1745 Plantae*4 Protista-References:...
by the IUCN because the population is expected to undergo a rapid decline. The primary threat to this species is the Brown Tree Snake
Brown tree snake
The brown tree snake is an arboreal rear-fanged colubrid snake native to eastern and northern coastal Australia, Papua New Guinea, and a large number of islands in northwestern Melanesia....
, a native of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
and the Solomon Islands
Solomon Islands
Solomon Islands is a sovereign state in Oceania, east of Papua New Guinea, consisting of nearly one thousand islands. It covers a land mass of . The capital, Honiara, is located on the island of Guadalcanal...
, which eliminated all 12 landbird species on nearby Guam after being accidentally 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...
. The snake recently arrived on Saipan, one of the two islands that compose the range of the Golden White-eye, and which holds the largest population of the species. The isolation of Aguijan makes the introduction of brown tree snakes there unlikely, but the small population there is vulnerable as the island is only 718 ha
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...
(1774 acres) in size and a direct hit by a supertyphoon
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
could wipe them out. Efforts are under way to breed the species in captivity
Ex-situ conservation
Ex-situ conservation means literally, "off-site conservation". It is the process of protecting an endangered species of plant or animal outside of its natural habitat; for example, by removing part of the population from a threatened habitat and placing it in a new location, which may be a wild...
and to control the snakes on Saipan. Six zoos have recently received this species and breeding was expected to begin by 2011. Success came more quickly, and the first captive birds were bred in 2009 in the North Carolina Zoo
North Carolina Zoo
The North Carolina Zoo is located in Asheboro in Randolph County, North Carolina in the Uwharrie Mountains near the geographic center of the state, approximately west of Raleigh, NC, United States. At , it is the largest "walk-through" natural-habitat zoo in the world, the first in the United...
. Birds from captive breeding will be introduced on new islands. In addition, translocations
Translocation (Wildlife conservation)
Translocation in wildlife conservation means capture, transport and release or introduction of species, habitats or other ecological material from one location to another...
of 50 birds from Saipan to the island of Sarigan
Sarigan
Sarigan is a small island in the Northern Mariana Island chain. It is the result of a Holocene Era stratovolcano with no known historic eruptions, although a swarm of volcano-tectonic earthquakes took place here in the summer of 2005....
, a predator-free island reserve, are currently being planned by scientists working to save the species.