The Golden White-eye (Cleptornis marchei) is a species of bird in the white-eye family Zosteropidae. It is monotypic within the genus Cleptornis. The Golden White-eye was once considered to be a honeyeater in the family Meliphagidae. 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 shares its range with (sympatry) and competes with the related Bridled White-eye. This bird has golden coloured plumage that gives it its name, and a pale eye-ring. It feeds on insects, fruit and nectar and forages in pairs or small family groups. The Golden White-eye is monogamous and lays two eggs in a small cup nest.

Fossil evidence shows the Golden White-eye's once also occurred on Tinian and Rota but has subsequently become extirpated in those locations due to the impact of human activities. In spite of its current abundance on Saipan and Aguijan, and the fact that it has amongst 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 zoos.

Taxonomy

The species was once called the Golden Honeyeater as it was considered to be a honeyeater and placed with the genus Ptilotis by Dr. Jean-Frédéric Émile Oustalet when he described the species in 1889 (that genus is now considered defunct and is no longer used). Behavioural and morphological characteristics led H. Douglas Pratt to suggest in 1987 that it was related to the white-eyes. Subsequent studies have supported the idea that it, along with the closely related Bonin White-eye, was in fact a white-eye. The species was moved to the genus Cleptornis which had been provisionally established by Oustalet in case the species proved to be distinct. It is possibly most closely related to the Micronesian white-eyes of the genus Rukia, or alternatively basal amongst 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.

Distribution and habitat The Golden White-eye is distributed on Saipan and Aguijan in the Northern Mariana Islands

The Golden White-eye is endemic to Northern Mariana Islands, where it currently occurs on the islands of Saipan and Aguijan. Within its range it occupies a range of habitats, both natural and man-made. It is common in native forests, particularly the limestone forests, but also occurs in open shrubland and suburban areas. On Saipan the only habitats it is generally absent from are the grassy savannas and the marshes around Lake Susupe.

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 g (0.7 oz). The species has bright, unmistakable plumage, with: a orange yellow head coupled with a pale eye-ring; a yellow-green back, wings, and tail; and golden orange undersides. Both the bill and legs are orange as well. The plumage of both sexes is similar; the males can be told from the females only when being examined in the hand, since the males have longer wings than the females. The juveniles of this species 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 that 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-eye, 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 passerines, 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.

Diet and feeding Golden White-eye feeding on bananas

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, for example the common forest tree Cynometra ramifolia is the preferred tree and used more frequently than the equally common Guamia mariannae. There is considerable overlap between their foraging range and those of the Bridled White-eye, but the Golden White-eye is more generalised in its diet. They also show some 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.

Breeding

Breeding occurs throughout the year on Saipan, where the species' nesting behaviour has been studied. However, the peak breeding period seems to be from March to July. The species is monogamous. The nests are simple undecorated cups of casuarina needles, grasses, and vines. These are placed around 2.9 m (between 1.5"?6.5 m) off the ground in a variety of tree species including Casuarina, Guamia, Cynometra, Leucaena and Citrus. The nests are predated by other bird species, specifically Micronesian Starlings and Collared Kingfishers. In addition, the introduced green tree skink has also been seen predating the nests.

The typical clutch size is two eggs, 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.

Threats and conservation Captive breeding is being attempted in some zoos to safeguard the future of this species.

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 as well.

At present the Golden White-eye is very common, and in fact a 1996 study found that their densities on Saipan were amongst the highest recorded for any bird, up to 2,095 birds/km², and the current world population is estimated at around 57,000 birds. It is believed that Saipan cannot sustain a larger population of this white-eye than it already does.

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 New Guinea and the Solomon Islands which eliminated all 12 landbird species on nearby Guam after being accidentally introduced. The snake recently arrived on the island of 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 small 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 is expected to begin by 2011. Birds from captive breeding will be introduced on new islands.