Capricorn silvereye
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The Capricorn silvereye (''Zosterops lateralis chlorocephalus''), also known as the Capricorn white-eye or green-headed white-eye, is a small greenish bird in the
Zosteropidae The white-eyes are a family, Zosteropidae, of small passerine birds native to tropical, subtropical and temperate Sub-Saharan Africa, southern and eastern Asia, and Australasia. White-eyes inhabit most tropical islands in the Indian Ocean, the ...
or white-eye
family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
. It is a subspecies of the
silvereye The silvereye or wax-eye (''Zosterops lateralis'') is a very small omnivorous passerine bird of the south-west Pacific. In Australia and New Zealand its common name is sometimes white-eye, but this name is more commonly used to refer to all membe ...
that occurs on islands off the coast of
Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , established_ ...
in north-eastern
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
, and which is sometimes considered to be a full species.


Description

The Capricorn silvereye is the only bird
endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
to the
Great Barrier Reef The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over over an area of approximately . The reef is located in the Coral Sea, off the coast of Queensland, ...
. It was first described by
Archibald Campbell Archibald Campbell may refer to: Peerage * Archibald Campbell of Lochawe (died before 1394), Scottish peer * Archibald Campbell, 2nd Earl of Argyll (died 1513), Lord Chancellor of Scotland * Archibald Campbell, 4th Earl of Argyll (c. 1507–1558) ...
and Samuel White in ''
The Emu ''Emu'', subtitled ''Austral Ornithology'', is the peer-reviewed scientific journal of BirdLife Australia (formerly the Royal Australasian Ornithologists Union). The journal was established in 1901 and is the oldest ornithological journal publ ...
'' from specimens collected during an expedition by the
Royal Australasian Ornithologists Union The Royal Australasian Ornithologists Union (RAOU), now part of BirdLife Australia, was Australia's largest non-government, non-profit, bird conservation organisation. It was founded in 1901 to promote the study and bird conservation, conservati ...
to the Capricorn Group in October 1910. They wrote:
''Zosterops'' were numerous, and appeared to breed on the islands, judging by a few old nests. As at some of our more southern camps, it was delightful to listen to the subdued chorus of the birds' sweet warbling songs at daybreak. Regularly on Masthead they commenced to warble from 10 to 5 minutes before 5 o’clock.
White-eyes were observed in great numbers on North-West and Tryon Islands, where, also, the nesting season had not yet commenced. Several skins were procured – the first by Mr J.W. Mellor.
From a critical examination of these skins it is at once noticeable that they are not referable to ''Z. caerulescens'', but are more in agreement with the description of Quoy and Gaimard’s ''Z. westernensis''. Should further research prove them different, we venture to suggest the name ''Z. chlorocephalus'', or Green-headed White-eye (on account of the "clean-cut" markings of that colour), the following being the general description: – ''Male''. – Distinct ring of silvery-white round the eye, succeeded by a black line under the eye; head, mantle, upper wing coverts, and upper tail coverts bright olive-green; back grey, blending into the greenish mantle; wings and tail dark brown, the primaries and tail feathers edged with bright olive-green; chin, throat, and under tail coverts greenish-yellow; rest of the under surface grayish-blue, darkest on the chest, and approaching grayish-white on the abdomen. Bill dark brown, the basal half of the lower mandible lighter coloured; tarsus dark grey. Dimensions in inches: – Length, 4 ¾ 21 mm wing, 2 11/16 8 mm bill, 7/16 1 mm tail, 2 1 mm tarsus, 11/16 7 mm
The sexes of the Capricorn silvereye are visually indistinguishable. The subspecies is substantially larger than ''Z. l. cornwalli'', the taxon occupying the mainland coast opposite the Capricorn and Bunker Islands, from which it is derived, and from which it has been separated for not more than four
millennia A millennium (plural millennia or millenniums) is a period of one thousand years, sometimes called a kiloannum (ka), or kiloyear (ky). Normally, the word is used specifically for periods of a thousand years that begin at the starting point (ini ...
, or about 500 generations, following its colonisation of the islands.Clegg et al. (2008). The bird has been used as a model to investigate the hypothesis that
passerine A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped'), which includes more than half of all bird species. Sometimes known as perching birds, passerines are distinguished from other orders of birds by t ...
s on islands have a tendency to evolve larger forms. The
lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...
is an unsexed specimen from
North West Island North West Island is a coral cay in the southern Great Barrier Reef, located 75 kilometres northeast of Gladstone, Queensland. North West Island forms part of Capricornia Cays National Park and with an area of 1.05 km2, the island is th ...
, held by the
American Museum of Natural History The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...
(AMNH 700956).Australian Faunal Directory.


Distribution and habitat

The Capricorn silvereye is restricted to wooded
coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...
cay A cay ( ), also spelled caye or key, is a small, low-elevation, sandy island on the surface of a coral reef. Cays occur in tropical environments throughout the Pacific, Atlantic, and Indian Oceans, including in the Caribbean and on the Great ...
s of the
Capricorn and Bunker Group The islands and reefs of the Capricorn and Bunker Group are situated astride the Tropic of Capricorn at the southern end of the Great Barrier Reef, approximately 80 kilometres east of Gladstone, which is situated on the central coast of the ...
at the southern end of the
Great Barrier Reef The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over over an area of approximately . The reef is located in the Coral Sea, off the coast of Queensland, ...
in
Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , established_ ...
. It is the only
passerine A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped'), which includes more than half of all bird species. Sometimes known as perching birds, passerines are distinguished from other orders of birds by t ...
species to breed regularly on 16 ha Heron Island. There it has been the subject of long-term biological studies by the
University of Queensland , mottoeng = By means of knowledge and hard work , established = , endowment = A$224.3 million , budget = A$2.1 billion , type = Public research university , chancellor = Peter Varghese , vice_chancellor = Deborah Terry , city = B ...
which operates the Heron Island Research Station, with the island population having been continuously and accurately monitored since 1965. Its habitat comprises typical cay vegetation of the region, mainly of ''
Pisonia grandis ''Pisonia grandis'', the grand devil's-claws, is a species of flowering tree in the ''Bougainvillea'' family, Nyctaginaceae. Description The tree has broad, thin leaves, smooth bark and bears clusters of green sweet-smelling flowers that matu ...
''
forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...
forming a closed canopy up to 15 m in height, with areas of ''
Casuarina equisetifolia ''Casuarina equisetifolia'', common names ''Coastal She-oak'' or ''Horsetail She-oak'' (sometimes referred to as the Australian pine tree or whistling pine tree outside Australia), is a she-oak species of the genus ''Casuarina''. The native ...
'', Silky Celtis, Sweet Sandpaper Fig, Octopus Bush and associated shrubs, as well as areas around human habitation, such as the Heron Island resort.Kikkawa & Wilson (1983).


Behaviour


Breeding

Studies on Heron Island have shown that Capricorn silvereyes mate for life with the same partner. They are not only socially, but also genetically monogamous birds, and their territories are actively defended by both members of the pair during the breeding season.Robertson et al. (2001). Breeding is seasonal, beginning in the dry season of winter and spring (August–November), with the peak of the first clutch laying occurring in September–October and the chicks hatching when early wet season rains have stimulated the availability of insects. With the onset of the nesting season, males start roosting by themselves and singing from a high, but often concealed, perch at dawn as they establish, or reestablish, their
territory A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
. The territory defended by a pair is usually restricted to the tree in which the nest is built, and its immediate vicinity. Beginning as early as August, nests are built in dense foliage, usually in a terminal fork of a ''Pisonia'' branch, though several other plants may be used. The cup-shaped nest is constructed by both members of the pair from dry grasses and other vegetable material, as well as cobwebs and various kinds of
anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Counterintuitively, anthropogenic may also refer to things that have been generated by humans, as follows: * Human im ...
debris such as toilet paper, fishing line and human hair. Nests may take up to a week or more to complete. The usual clutch is of three pale blue eggs, with an incubation period of 12–14 days. The hatchlings are
altricial In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...
and
nidicolous In biology, nidifugous ( , ) organisms are those that leave the nest shortly after hatching or birth. The term is derived from Latin ''nidus'' for "nest" and ''fugere'', meaning "to flee". The terminology is most often used to describe birds and w ...
and are fed by both parents. The chicks
fledge Fledging is the stage in a flying animal's life between hatching or birth and becoming capable of flight. This term is most frequently applied to birds, but is also used for bats. For altricial birds, those that spend more time in vulnerable c ...
at 12–14 days old and leave the nest shortly afterwards, still being fed by their parents for about another two weeks. In a study of the 1969/70 breeding season, the mean number of fledglings produced per nest was 1.9. Second and third clutches extend breeding through much of the wet season into January.


Feeding

The silvereyes forage in small flocks, or sometimes singly when feeding young. They are not confined to their breeding territories, though the adults forage near them from the ground to the forest canopy, often around concentrated food sources. They consume a wide range of plant and animal food, including insects and other small invertebrates, fruit and nectar. The sweet sandpaper fig is an important source of food on Heron Island.Higgins et al. (2006).


Vocalisation

The song of the Capricorn silvereye is a warble containing a series of separate notes; it is complex, with a well-organised hierarchy of syllables and sequences. A bird's song repertoire is established by its first breeding season. Singing takes place in the breeding season during a 20-minute dawn chorus by all territorial males; it is also heard occasionally throughout the day. The song rate averages six to seven songs per minute during the dawn chorus; each song is about five seconds long and contains an average of 16 notes.Slater (1993).


Population and mortality

A study of population dynamics on 16 ha Heron Island between 1979 and 1993, during which over 90% of the birds were individually colour-banded, recorded that the population there fluctuated between 225 and 483 individuals. Four
cyclone In meteorology, a cyclone () is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above (opposite to an anti ...
s during that period caused substantial mortality. There was also evidence of the effects of density dependence in the size of the adult population, and with fledgling survival decreasing with the numbers of birds attempting to breed.McCallum (2000). The main cause of the total loss of nestlings from a nest is faulty nest construction leading to tilting. Early dry season nests can suffer damage from the loss of supporting leaves in the tree canopy, while late season nests are at risk from heavy rain and strong winds. Young fledglings are vulnerable to predation by
eastern reef egret The Pacific reef heron (''Egretta sacra''), also known as the eastern reef heron or eastern reef egret, is a species of heron found throughout southern Asia and Oceania. It occurs in two colour morphs with either slaty grey or pure white pluma ...
s in the trees, and by
silver gull The silver gull (''Chroicocephalus novaehollandiae'') is the most common gull of Australia. It has been found throughout the continent, but particularly at or near coastal areas. It is smaller than the Pacific gull (''Larus pacificus''), which ...
s and
buff-banded rail The buff-banded rail (''Hypotaenidia philippensis'') is a distinctively coloured, highly dispersive, medium-sized rail of the rail family, Rallidae. This species comprises several subspecies found throughout much of Australasia and the south-we ...
s on the ground.


References


Notes


Sources

* * * * * * * * * * * * * {{Taxonbar, from=Q5036263
Capricorn silvereye The Capricorn silvereye (''Zosterops lateralis chlorocephalus''), also known as the Capricorn white-eye or green-headed white-eye, is a small greenish bird in the Zosteropidae or white-eye family. It is a subspecies of the silvereye that occu ...
Birds of Queensland Endemic birds of Australia Great Barrier Reef
Capricorn silvereye The Capricorn silvereye (''Zosterops lateralis chlorocephalus''), also known as the Capricorn white-eye or green-headed white-eye, is a small greenish bird in the Zosteropidae or white-eye family. It is a subspecies of the silvereye that occu ...