Capricorn Silvereye
Encyclopedia
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 occurs on islands off the coast of Queensland
in north-eastern Australia
, and which is sometimes considered to be a full species.
. It was first described by Archibald Campbell
and Samuel White
in The Emu
from specimens collected during an expedition by the Royal Australasian Ornithologists Union
to the Capricorn Group in October 1910. They wrote:
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
, or about 500 generations, following its colonisation of the islands. The bird has been used as a model to investigate the hypothesis that passerine
s on islands have a tendency to evolve larger forms. The lectotype
is an unsexed specimen from North West Island
, held by the American Museum of Natural History
(AMNH 700956).
cay
s of the Capricorn and Bunker Group
at the southern end of the Great Barrier Reef
in Queensland
. It is the only passerine
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
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
forest
forming a closed canopy up to 15 m in height, with areas of Casuarina equisetifolia
, Silky Celtis
, Sweet Sandpaper Fig
, Octopus Bush
and associated shrubs, as well as areas around human habitation, such as the Heron Island resort.
. 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 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
and nidicolous
and are fed by both parents. The chicks fledge
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.
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.
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.
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
s in the trees, and by Silver Gull
s and Buff-banded Rail
s on the ground.
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
. It is a subspecies of the Silvereye
Silvereye
The Silvereye or Wax-eye is a very small passerine bird native to Australia, New Zealand and the south-west Pacific islands of Lord Howe, New Caledonia, Loyalty Islands, Vanuatu, and Fiji...
that occurs on islands off the coast of Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
in north-eastern 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...
, and which is sometimes considered to be a full species.
Description
The Capricorn Silvereye is the only bird endemic to the Great Barrier ReefGreat Barrier Reef
The Great Barrier Reef is the world'slargest reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometres over an area of approximately...
. It was first described by Archibald Campbell
Archibald James Campbell
Archibald James Campbell was an Australian civil servant in the Victorian, later the Australian federal, customs service, as well as an amateur ornithologist. He was one of the principal founders of the Royal Australasian Ornithologists Union in 1901 and served as its President in 1909 and 1928...
and Samuel White
Samuel Albert White
Captain Samuel Albert White was a wealthy Australian racehorse owner, soldier, explorer, conservationist and amateur ornithologist. He was born in Fulham, South Australia and eventually died there. He fought in the South African War 1900-1903, reaching the rank of Captain, which title he...
in The Emu
Emu (journal)
Emu, subtitled Austral Ornithology, is the peer-reviewed scientific journal of the Royal Australasian Ornithologists Union. The journal was established in 1901 and is the oldest ornithological journal published in Australia...
from specimens collected during an expedition by the Royal Australasian Ornithologists Union
Royal Australasian Ornithologists Union
The Royal Australasian Ornithologists Union, also known as Birds Australia, was founded in 1901 to promote the study and conservation of the native bird species of Australia and adjacent regions. This makes it Australia's oldest national birding association. It is also Australia's largest...
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 [121 mm]; wing, 2 11/16 [68 mm]; bill, 7/16 [11 mm]; tail, 2 [51 mm]; tarsus, 11/16 [17 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
Millennium
A millennium is a period of time equal to one thousand years —from the Latin phrase , thousand, and , year—often but not necessarily related numerically to a particular dating system....
, or about 500 generations, following its colonisation of the islands. The bird has been used as a model to investigate the hypothesis that 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 on islands have a tendency to evolve larger forms. The lectotype
Lectotype
In botanical nomenclature and zoological nomenclature, a lectotype is a kind of name-bearing type. When a species was originally described on the basis of a name-bearing type consisting of multiple specimens, one of those may be designated as the lectotype...
is an unsexed specimen from North West Island
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 the second largest coral cay in the Great Barrier Reef...
, held by the American Museum of Natural History
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
(AMNH 700956).
Distribution and habitat
The Capricorn Silvereye is restricted to wooded coralCoral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
cay
Cay
A cay , also spelled caye or key, is a small, low-elevation, sandy island formed on the surface of coral reefs. Cays occur in tropical environments throughout the Pacific, Atlantic and Indian Oceans , where they provide habitable and agricultural land for hundreds of thousands of people...
s of the Capricorn and Bunker Group
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 Queensland....
at the southern end of the Great Barrier Reef
Great Barrier Reef
The Great Barrier Reef is the world'slargest reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometres over an area of approximately...
in Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
. It is the only 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...
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
University of Queensland
The University of Queensland, also known as UQ, is a public university located in state of Queensland, Australia. Founded in 1909, it is the oldest and largest university in Queensland and the fifth oldest in the nation...
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
Pisonia grandis 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 mature into sticky barbed seeds....
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...
forming a closed canopy up to 15 m in height, with areas of Casuarina equisetifolia
Casuarina equisetifolia
Casuarina equisetifolia is a she-oak species of the genus Casuarina. The native range extends from Burma and Vietnam throughout Malesia east to French Polynesia, New Caledonia, and Vanuatu, and south to Australia...
, Silky Celtis
Celtis paniculata
Celtis paniculata is a coastal rainforest tree. In Australia it occurs from Kiama in New South Wales to the Endeavour River in tropical Queensland. It also grows at Norfolk Island, Eastern Malesia, Micronesia, and Western Polynesia...
, Sweet Sandpaper Fig
Ficus opposita
Ficus opposita is one of several fig species commonly known as Sandpaper Figs. It is native to the Northern Territory and Queensland in Australia.Other common names include Sweet Sandpaper Fig, Sweet Fig and the ambiguous "figwood" and "watery fig".It grows as either a shrub or small tree.As the...
, Octopus Bush
Heliotropium foertherianum
Heliotropium foertherianum is a species of flowering plant in the borage family, Boraginaceae. It is native to tropical Asia, including southern China, Madagascar, northern Australia, and most of the atolls and high islands of Micronesia and Polynesia. Common names include Tree Heliotrope, Velvet...
and associated shrubs, as well as areas around human habitation, such as the Heron Island resort.
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. 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 territoryTerritory (animal)
In ethology the term territory refers to any sociographical area that an animal of a particular species consistently defends against conspecifics...
. 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 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
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...
and nidicolous
Nidicolous
Nidicolous animals are those that stay at their nest or birthplace for a long time after birth, due to their dependence on the parents for feeding, protection and learning survival skills...
and are fed by both parents. The 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...
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.Vocalisation
The song of the Capricorn Silverye 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 chorusDawn chorus (birds)
The dawn chorus occurs when songbirds sing at the start of a new day. In temperate countries, this is most noticeable in spring, when the birds are either defending a breeding territory or trying to attract a mate. In a given location, it is common for different species to do their dawn singing at...
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.
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 cycloneCyclone
In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale...
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.
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
Eastern Reef Egret
The Eastern Reef Heron , also known as the Pacific Reef Egret or Eastern Reef Egret, is a kind of heron. They are found in many areas of Asia including the oceanic region of India, Southeast Asia, Japan, Polynesia, and in Australia, Tasmania and New Zealand.Pacific Reef Herons are medium-sized...
s in the trees, and by Silver Gull
Silver Gull
The Silver Gull also known simply as "seagull" in Australia, is the most common gull seen in Australia. It has been found throughout the continent, but particularly coastal areas. The South African Hartlaub's Gull and the New Zealand Red-billed Gull The Silver Gull (Chroicocephalus...
s and Buff-banded Rail
Buff-banded Rail
The Buff-banded Rail, Gallirallus philippensis is a distinctively coloured, highly dispersive, medium-sized rail of the family Rallidae....
s on the ground.