The Christmas imperial pigeon (''Ducula whartoni''), also known as Black imperial pigeon, Dusky imperial pigeon, Wharton's imperial pigeon, or burong pergam , is a large
imperial pigeon
''Ducula'' is a genus of the pigeon family Columbidae, collectively known as imperial pigeons. They are large to very large pigeons with a heavy build and medium to long tails. They are arboreal, feed mainly on fruit and are closely related to th ...
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
Christmas Island
Christmas Island, officially the Territory of Christmas Island, is an Australian external territory comprising the island of the same name. It is located in the Indian Ocean, around south of Java and Sumatra and around north-west of the ...
in the northeastern
Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by th ...
. It has an overall grey-blue colouration, and juveniles are duller than adults. It makes a soft purring coo sound and a deeper ''whoo'' sound comparable to a cow mooing. It lays one glossy white egg per brood, and is possibly somewhat colonial.
Other than the
Christmas Island flying fox, the Christmas imperial pigeon is the only fruit-eating (
frugivorous
A frugivore is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts and seeds. Approximately 20% of mammalian herbivores eat fruit. Frugivores are highly dependent on the abundance and ...
) animal on the island, and the pigeon feeds and nests in the dense
canopy
Canopy may refer to:
Plants
* Canopy (biology), aboveground portion of plant community or crop (including forests)
* Canopy (grape), aboveground portion of grapes
Religion and ceremonies
* Baldachin or canopy of state, typically placed over an a ...
. It mainly inhabits the tropical inland plateau, and widespread non-native
Jamaican cherry forests. It was previously thought to be in danger of extinction due to habitat loss and
invasive species
An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
(specifically the
yellow crazy ant
The yellow crazy ant (''Anoplolepis gracilipes''), also known as the long-legged ant or Maldive ant, is a species of ant, thought to be native to West Africa or Asia. They have been accidentally introduced to numerous places in the world's trop ...
), but it is now considered to be rather common, with a breeding population of about 5,000.
Taxonomy
The Christmas imperial pigeon was first described by English ornithologist
Richard Bowdler Sharpe
Richard Bowdler Sharpe (22 November 1847 – 25 December 1909) was an English zoologist and ornithologist who worked as curator of the bird collection at the British Museum of natural history. In the course of his career he published several mono ...
in 1887 based on an adult male specimen collected by Captain
John Maclear
John Fiot Lee Pearse Maclear (27 June 1838 in Cape Town – 17 July 1907 in Niagara) was an admiral in the Royal Navy, known for his leadership in hydrography.
He is best known for being commander of during the ''Challenger'' Expedition (18 ...
of . The
species name
In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...
''whartoni'' honours British admiral
Sir William Wharton. It is unclear how Sharpe and Wharton are affiliated, but Wharton was made a
Fellow of the Royal Society
Fellowship of the Royal Society (FRS, ForMemRS and HonFRS) is an award granted by the judges of the Royal Society of London to individuals who have made a "substantial contribution to the improvement of natural science, natural knowledge, incl ...
in the previous year, possibly somehow affecting Sharpe's thinking. Sharpe first classified it into the now-defunct
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''Carpophaga''. In 1933, English zoologist
Frederick Nutter Chasen
Frederick Nutter Chasen (1896 – 13 February 1942) was an English zoologist.
Chasen was born in Norfolk, England. He was apprenticed to Frank Leney of the Norwich Museum in 1912, joining the Museum as a full-time employee in 1919. Between thes ...
considered the Christmas imperial pigeon to be a
subspecies
In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
of
pink-headed imperial pigeon
The pink-headed imperial pigeon (''Ducula rosacea'') is a species of bird in the family Columbidae found in the Lesser Sunda Islands of Indonesia. Its natural habitats are subtropical or tropical moist lowland forests, subtropical or tropical man ...
as ''D. rosacea whartoni''. In 1937, American ornithologist
James L. Peters
James Lee Peters (August 13, 1889 – April 19, 1952) was an American ornithologist.
He was born in Boston, Massachusetts to Dr. Austin Peters and Francis Howie Lee on August 13, 1889. His early education was at the Roxbury Latin School, followe ...
synonymised ''Carpophaga'' with ''Drucula'', and disagreed with Chasen, classifying the Christmas imperial pigeon as a distinct species, ''D. whartoni''.
The Christmas imperial pigeon is a species of
imperial pigeon
''Ducula'' is a genus of the pigeon family Columbidae, collectively known as imperial pigeons. They are large to very large pigeons with a heavy build and medium to long tails. They are arboreal, feed mainly on fruit and are closely related to th ...
(''Ducula''), which is widely spread out across
Oceania
Oceania (, , ) is a region, geographical region that includes Australasia, Melanesia, Micronesia, and Polynesia. Spanning the Eastern Hemisphere, Eastern and Western Hemisphere, Western hemispheres, Oceania is estimated to have a land area of ...
, however it is the only imperial pigeon in the Indian Ocean. Likewise, its
affinities are unclear.
However, the Christmas imperial pigeon could be placed into the ''
D. aenea''
species complex
In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...
along with the green (
nominate
Nomination is part of the process of selecting a candidate for either election to a public office, or the bestowing of an honor or award. A collection of nominees narrowed from the full list of candidates is a short list.
Political office
In the ...
),
island
An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island ...
,
grey
Grey (more common in British English) or gray (more common in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is "without color", because it can be composed o ...
, and pink-headed imperial pigeons. The latter is sometimes considered synonymous with the Christmas imperial pigeon.
Description
An adult Christmas imperial pigeon male measures on average , and females . In males, the wing averages , and in females . The average male weighs , and female . It is rather large for imperial pigeons, though relatively lightly built.
[
It has an overall grey-black colour,][ with darker feathers on the top portion, and lighter feathers on the breast and belly with a ]burgundy
Burgundy (; french: link=no, Bourgogne ) is a historical territory and former administrative region and province of east-central France. The province was once home to the Dukes of Burgundy from the early 11th until the late 15th century. The c ...
tinge.[ The beak is black. There is a narrow white band on the base of the upper beak. The eye colour ranges from yellow to orange. The ]nape
The nape is the back of the neck. In technical anatomical/medical terminology, the nape is also called the nucha (from the Medieval Latin rendering of the Arabic , "spinal marrow"). The corresponding adjective is ''nuchal'', as in the term ''nu ...
and back have a glossy oil-green colour. The wings have glossy bluish-green tips, and are greyish-brown nearer the base. The tail has broad, greenish-brown tips with a somewhat scalloped appearance, and the legs and underside of the tail have reddish-brown feathers. The feet are purple-red.[
Juveniles look similar to adults, but have a duller colouration without the oil-green gloss from the lower back to the tail coverts, with a brown breast and belly, a dull grey crown, and grey-brown feet. Eye colour is dark brown.][
The Christmas imperial pigeon is known to make a soft gurgling or purring coo sound. It can also make a deep ''whoo'' or ''croo-croo-croo'' sound which has also been compared to a cow mooing in the distance. It sometimes makes loud clapping sounds with its wings, but in flight, it is largely quiet.][
]
Breeding
Males have been observed to engage in a courtship display
A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), ...
, a "perch coo". A male will slightly puff up its chest, press his bill against it, hold his wings close, and will emit a loud ''coo'' before lowering his body to an almost horizontal position. It will rhythmically repeat this motion.
The Christmas imperial pigeon generally constructs nests in the dense forest canopy
Canopy may refer to:
Plants
* Canopy (biology), aboveground portion of plant community or crop (including forests)
* Canopy (grape), aboveground portion of grapes
Religion and ceremonies
* Baldachin or canopy of state, typically placed over an a ...
. One nest was observed to have been in diameter, thick, and constructed using only dead twigs off the ground in a non-native white leadtree. Peak breeding season may be from November to April. Breeding season is from at least August to April, though predominantly November to March, and the pigeon may be somewhat colonial. It lays a single egg per brood—on rare occasions two—and may lay two broods per year.[
One observed chick, probably 10–13 days old, was measured to be long, with developing ]covert
Secrecy is the practice of hiding information from certain individuals or groups who do not have the "need to know", perhaps while sharing it with other individuals. That which is kept hidden is known as the secret.
Secrecy is often controvers ...
and secondary
Secondary may refer to: Science and nature
* Secondary emission, of particles
** Secondary electrons, electrons generated as ionization products
* The secondary winding, or the electrical or electronic circuit connected to the secondary winding i ...
feathers, and emerging primary feather
Flight feathers (''Pennae volatus'') are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those on the tail ...
s. By age 22 days, the chick resembled a small adult, except with remnants of down feather
The down of birds is a layer of fine feathers found under the tougher exterior feathers. Very young birds are clad only in down. Powder down is a specialized type of down found only in a few groups of birds. Down is a fine thermal insulator an ...
s on the breast and belly, brown feet and irises, and duller plumage. It 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 ...
d (became capable of flight) upon reaching 70% of full size at age 24–27 days, and remained dependent on parental care for 17 more days. The chick was fed over a period of 5 to 15 minutes. The chick prodded its parent's throat, and then inserted its beak for about 12 seconds, and did this twice per minutes. Feeding was observed between 9–10 A.M., but probably occurred again in the evening or nighttime. Outside of feeding, it was left alone in the nest, but may have been accompanied through the night.[
An egg taken in 1914 was observed to be a broad-elliptical shape, white, slightly glossy, and measured .][
]
Habitat and distribution
The species is 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 tropical Christmas Island
Christmas Island, officially the Territory of Christmas Island, is an Australian external territory comprising the island of the same name. It is located in the Indian Ocean, around south of Java and Sumatra and around north-west of the ...
in the eastern Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by th ...
.[ It predominantly inhabits the evergreen inland plateau, but is found throughout the island.][ Though about a third of this was cut down for ]phosphate mining
In chemistry, a phosphate is an anion, salt (chemistry), salt, functional group or ester derived from a phosphoric acids and phosphates, phosphoric acid. It most commonly means orthophosphate, a derivative of phosphoric acid, orthophosphoric a ...
, the introduced Jamaican cherry trees has recolonized many areas. It was introduced to the Coco Islands
The Coco Islands ( my, ကိုကိုးကျွန်း) are a small group of islands in the northeastern Bay of Bengal. They are part of the Yangon Region of Myanmar. The islands are located south of the city of Yangon. Coco Island gr ...
(probably Horsburgh Island
Horsburgh Island (in Malay, Pulo Luar or Pulu Luar) is one of the Cocos (Keeling) Islands. Its area is . There is a small lagoon in the interior of the island to the northeast.
History
The Clunies-Ross Family kept deer on the island for hunting ...
) sometime between November 1888 and August 1890, with the last sighting made in 1906.
Ecology
The Christmas imperial pigeon, along with the Christmas Island flying fox, are the only 2 major fruit-eating (frugivorous
A frugivore is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts and seeds. Approximately 20% of mammalian herbivores eat fruit. Frugivores are highly dependent on the abundance and ...
) animals on the island. As such, the pigeon plays an important role in seed dispersal
In Spermatophyte plants, seed dispersal is the movement, spread or transport of seeds away from the parent plant.
Plants have limited mobility and rely upon a variety of dispersal vectors to transport their seeds, including both abiotic vectors, ...
, seeds swallowed whole and remaining intact[ (imperial pigeons are able to stretch the base of the jaw to eat larger food items.][) They have been reported feeding on smaller seeded plants such as the ]stinkwood Stinkwood, german ''Stinkholz'', french ''Bois Puant'', is the common name for a number of trees or shrubs which have wood or plant parts with an unpleasant odour, including:
*'' Anagyris foetida''; Southern Europe
*'' Bignonia callistegioides'' (c ...
''Celtis timorensis
''Celtis timorensis'', commonly known as stinkwood or stinking wood, is a species of flowering plant in the family Cannabaceae that grows in tropical Asia. The specific name (botany), specific epithet comes from the name of the island of Timor, t ...
'', the common fig
The fig is the edible fruit of ''Ficus carica'', a species of small tree in the flowering plant family Moraceae. Native to the Mediterranean and western Asia, it has been cultivated since ancient times and is now widely grown throughout the world ...
, the chinaberry tree, ''Syzygium nervosum
''Syzygium nervosum'' is a species of tree native to tropical Asia and Australia, extending as far north as Guangdong and Guangxi in China and as far south as the Northern Territory of Australia. It was previously known as ''Cleistocalyx opercul ...
'', ''Tristiropsis acutangula
''Tristiropsis acutangula '' is a tree species of the genus ''Tristiropsis'' in the family Sapindaceae. It grows naturally in the Malesian biogeographical region and in northern Australia.
Description
It is a large forest canopy tree growing up ...
'', and the introduced Jamaican cherry. The latter has become a very important food source, with sightings of several hundreds of pigeons where the plant is common.[
It generally feeds in flocks in the canopy, isolated trees, or shrubs, and descends to drink from springs or puddles.][ It has also been observed feeding singly or in pairs.][ Though frugivorous, the pigeon has been observed repeatedly consuming the leaves of the introduced ]papaya
The papaya (, ), papaw, () or pawpaw () is the plant species ''Carica papaya'', one of the 21 accepted species in the genus ''Carica'' of the family Caricaceae. It was first domesticated in Mesoamerica, within modern-day southern Mexico and ...
plant (folivory
In zoology, a folivore is a herbivore that specializes in eating leaves. Mature leaves contain a high proportion of hard-to-digest cellulose, less energy than other types of foods, and often toxic compounds.Jones, S., Martin, R., & Pilbeam, D. (1 ...
), which may have been caused by an island-wide shortage of fruit or, less likely, for some therapeutic reason. Peak foraging time appears to be just before dusk.[
The ]Christmas goshawk
The Christmas goshawk (''Accipiter fasciatus natalis'') or Christmas Island goshawk, is a bird of prey in the goshawk and sparrowhawk family Accipitridae. It is a threatened endemic of Christmas Island, an Australian territory in the eastern Ind ...
has been observed preying on a Christmas imperial pigeon chick.[
]
Conservation
The Christmas imperial pigeon is classified as least concern by the IUCN Red List of Threatened Species
The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biologi ...
and is not protected by the Australian Environment Protection and Biodiversity Conservation Act 1999
The ''Environment Protection and Biodiversity Conservation Act 1999'' (Cth) is an Act of the Parliament of Australia that provides a framework for protection of the Australian environment, including its biodiversity and its natural and cultu ...
because, though its moderately small population is restricted to an island, it appears to be stable with no indication of significant future decline.[ It is possible that the population fluctuated from the initial settlement of the island in 1888 to the 1970s, with reports of a minor decline. In 1975, ornithologist ]Gerard Frederick van Tets
Gerard Frederick van Tets (19 January 1929 – 14 January 1995), otherwise known as Jerry van Tets, was a twentieth century British, Canadian and Australian ornithologist and palaeontologist. Born to Dutch parents, jhr. Hendrik Barthout van ...
guessed the total population to be 20 to 200 birds. A 2000 survey estimated the breeding population to be 1,000, and predicted that, due to the rapid spread of the invasive
Invasive may refer to:
*Invasive (medical) procedure
*Invasive species
*Invasive observation, especially in reference to surveillance
*Invasively progressive spread of disease from one organ in the body to another, especially in reference to cancer ...
yellow crazy ant
The yellow crazy ant (''Anoplolepis gracilipes''), also known as the long-legged ant or Maldive ant, is a species of ant, thought to be native to West Africa or Asia. They have been accidentally introduced to numerous places in the world's trop ...
, there would be an 80% decline in the pigeon's population over the next 12 years, making it critically endangered. Conversely, a 2003 survey estimated 35,000–66,000 individuals.[ The ]International Union for Conservation of Nature
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
(IUCN) lists the population as 5,000 mature individuals, and the pigeon is considered to be common with no major concerns of decline.[
]
Threats
Hunting was, historically, the main threat to the Christmas imperial pigeon, and the seeding of Japanese cherry trees along roadsides made it easier game, but the practice was made illegal in 1977.[
A 1994 survey found the diet of ]feral cats
A feral cat or a stray cat is an unowned domestic cat (''Felis catus'') that lives outdoors and avoids human contact: it does not allow itself to be handled or touched, and usually remains hidden from humans. Feral cats may breed over dozens ...
consisted predominantly of Christmas imperial pigeon, Christmas Island flying fox, and invasive rats. However, these were more likely scavenged than hunted.
Though there is no quantitative evidence, there are anecdotal reports of yellow crazy ants attacking birds or disturbing nests. Infestations of scale insect
Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than the ...
s, caused by their mutualistic relationship with the ants, has negatively impacted the canopy, and, in the long-term, could lead to decline of the habitat's health. The reduction of the Christmas Island red crab
The Christmas Island red crab (''Gecarcoidea natalis'') is a species of land crab that is endemic to Christmas Island and Cocos (Keeling) Islands in the Indian Ocean. Although restricted to a relatively small area, an estimated 43.7 million adu ...
population due to the ants has led to the germination of plants which otherwise would have been eaten by the crabs, which could eventually dramatically alter forest structure.
The yellow crazy ant population is controlled by placing bait laced with the insecticide
Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...
Fipronil
Fipronil is a broad-spectrum insecticide that belongs to the phenylpyrazole chemical family. Fipronil disrupts the insect central nervous system by blocking the ligand-gated ion channel of the GABAA receptor and glutamate-gated chloride (GluCl ...
. Surveys from spring 2002 and fall 2003 indicate a reduction in imperial pigeon populations in baited areas, though this may simply be due to seasonal differences in habitation. Nonetheless, ingestion of Fipronil is known to affect feeding behaviour, reproduction, and egg viability in other birds in the long term.
See also
* Birds of Christmas Island
The Birds of Christmas Island form a heterogeneous group of 162 species. There is a core group of 4 endemics that have evolved on the remote island in the eastern Indian Ocean for thousands of years, attended by a suite of regular migrants, oppor ...
References
Further reading
*
External links
DEH - Christmas Island fauna - birds
{{Taxonbar, from=Q948750
Ducula
Birds of Christmas Island
Near threatened biota of Oceania
Vulnerable fauna of Australia
Birds described in 1887