| Golden white-eye | |
|---|---|
 | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Passeriformes |
| Family: | Zosteropidae |
| Genus: | Cleptornis Oustalet, 1889 |
| Species: | C. marchei |
| Binomial name | |
| Cleptornis marchei | |
| Synonyms | |
Ptilotis marchei | |
Thegolden white-eye (Cleptornis marchei) is a species ofbird in the white-eye family,Zosteropidae. It is theonly species within thegenusCleptornis. The golden white-eye was once considered to be ahoneyeater in the family Meliphagidae and although it is now known to be a white-eye, its position within that family is still uncertain. Thespecies is restricted to the islands ofSaipan andAguijan in theNorthern Mariana Islands, where it issympatric (shares its range) and competes with the relatedbridled white-eye. The golden white-eye has goldenplumage 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 twoeggs in a small cupnest.
Fossil evidence shows the golden white-eye once also occurred onTinian andRota but wasextirpated 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 beEndangered. It is threatened by theinvasivebrown tree snake, which has becomeestablished on nearby Guam, and this predator is expected to cause a rapid decline in the population if it reaches Saipan. Efforts are under way to control the snakes andbreed the white-eye inzoos.
The species was once called thegolden honeyeater as it was considered to be ahoneyeater (Meliphagidae). It was placed within the genusPtilotis by French naturalistÉmile Oustalet when he described the species in 1889; that genus is now considered defunct and is no longer used.[4] It was subsequently moved into the genusCleptornis, which had been provisionally established by Oustalet in case the species proved to be distinct.[2] Behavioural and morphological characteristics led American ornithologistHarold Douglas Pratt, Jr., to suggest in 1987 that it was related to thewhite-eyes.[5]
Subsequent studies have supported the idea that this species was a white-eye.[6] It is possibly most closely related to theMicronesian white-eyes of the genusRukia, or the monotypicBonin white-eye (Apalopteron), another species once placed with the honeyeaters and subsequently moved to the white-eyes.[2] The golden white-eye has a long 10thprimary feather (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 isbasal (an early offshoot) among the white-eyes.[6]
Its generic name,Cleptornis, is derived from theAncient Greekkleptes, a robber or thief, andornis, a bird. This is not a reference to any aspect of the golden white-eye's behaviour, but to the oldFrench name of the Mariana Islands,les Îles des Voleurs, or Robbers' Islands.[7] Thespecific epithetmarchei refers to the French explorer and writerAntoine-Alfred Marche, who procured the original specimens.[8]
The golden white-eye isendemic to theNorthern Mariana Islands in the western Pacific Ocean, where it currently occurs on the islands ofSaipan andAguijan. Within its range, it occupies a variety ofhabitats, both natural and man-made. It is common in nativeforests, particularlylimestone forests, but also occurs in openshrubland andsuburban areas. On Saipan, the only habitats it is absent from are the marshes around Lake Susupe and grassysavannas.[2]
The golden white-eye differs from the other white-eyes in having large eyes and an outermostprimary 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, unmistakableplumage, 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.[2]
The golden white-eye makes a variety ofcalls. 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.[2]
Like other white-eyes, the golden white-eye isdiurnal. In contrast to thebridled 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.[9] The golden white-eye is alsoterritorial, and pairs willsing 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 forestpasserines, it is less aggressive towards them, and in fact therufous 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 theMicronesian myzomela and is chased by that species. It is also occasionally chased by the fantails if it approaches their nests too closely.[10]
The golden white-eye is a generalist, feeding on fruit, berries, andinsects.[9] 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.[11] Insects may be eithergleaned from the bark of trees and from leaves, or caught in the air. Certain tree species are preferred as foraging habitat. The common forest treeCynometra ramifolia is the most favoured tree and used more frequently than the equally commonGuamia 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 theforest canopy, and the golden white-eye feeding in both the canopy andunderstory 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.[12] 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.[9] 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 bytyphoons, which can dramatically alter the structure of the forest.[12]
Breeding occurs throughout the year on Saipan, where the species' nesting behaviour has been studied.[13] The peak breeding period seems to be from March to July.[4] The species ismonogamous. Thenests are simple undecorated cups ofcasuarina 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 includingCasuarina,Guamia,Cynometra,Leucaena, andCitrus.[13] The nests arepredated by other bird species, specificallyMicronesian starlings andcollared kingfishers,[14] as well as theintroducedgreen tree skink.[4]
The typicalclutch 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.[13] Both sexes share theincubation 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 bridled white-eyes, rufous fantails, and other golden white-eyes.[4] From laying it takes about two weeks for the eggs to hatch. The hatchlings arealtricial, in other words naked and helpless. Both parents share the brooding and feeding duties, and take awayfaecal sacs to keep the nest clean. The diet of the chicks is almost exclusively composed of insects and caterpillars. Chicksfledge around 10–14 days after hatching.[13] After fledging they may remain with their parents in small groups for some time.[9]
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 ofTinian andRota, and it may once have occurred onGuam and other islands in the Marianas.[15]
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).[10] It was believed that Saipan cannot sustain a larger population of this white-eye than it already does.[16] 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 thenightingale 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.[17]
The species is nonetheless evaluated asEndangered by theIUCN because the population is expected to undergo a rapid decline if thebrown tree snake becomes established on Saipan.[1] The primary threat to this species is thebrown tree snake,[1] a native ofAustralia,New Guinea and theSolomon Islands, which eliminated all 12 landbird species on nearby Guam after being accidentallyintroduced.[18] The snake has not yet become established 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.[1] 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 718ha (1774 acres) in size and a direct hit by asupertyphoon could wipe them out.[19] Efforts are under way to breed the speciesin captivity[20] and to prevent the snakes from being introduced and established on Saipan.[21] Six zoos have recently received this species and breeding was expected to begin by 2011.[4] Success came more quickly, and the first captive birds were bred in 2009 in theNorth Carolina Zoo.[22] Birds from captive breeding will be introduced on new islands.[4] In addition, 24 birds weretranslocated from Saipan to the island ofSarigan, a predator-free island reserve, in 2011 in the hope of establishing a breeding population.[1]
Media related toCleptornis marchei at Wikimedia Commons
Data related toCleptornis marchei at Wikispecies
