''Ducula'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of the pigeon family
Columbidae
Columbidae () is a bird family consisting of doves and pigeons. It is the only family in the order Columbiformes. These are stout-bodied birds with short necks and short slender bills that in some species feature fleshy ceres. They primarily ...
, 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 the other genus of fruit-eating doves,
''Ptilinopus''. Both genera display brightly coloured plumage, predominantly green, often with contrasting under-parts of purple, orange or red. Some ''Ducula'' have prominently swollen
ceres
Ceres most commonly refers to:
* Ceres (dwarf planet), the largest asteroid
* Ceres (mythology), the Roman goddess of agriculture
Ceres may also refer to:
Places
Brazil
* Ceres, Goiás, Brazil
* Ceres Microregion, in north-central Goiás ...
.
They have large gapes and swallow seeds whole, playing an important role in seed dispersal.
Imperial pigeons are found in forests of southern
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
,
New Guinea
New Guinea (; Hiri Motu: ''Niu Gini''; id, Papua, or , historically ) is the world's second-largest island with an area of . Located in Oceania in the southwestern Pacific Ocean, the island is separated from Australia by the wide Torr ...
, northern
Australia and the
Pacific islands. Many species are nomadic, travelling long distances to exploit seasonal fruit sources. Some undertake migrations and all are strong fliers.
Because of habitat loss and predation, species of ''Ducula'' are amongst the most threatened of avian species globally.
Taxonomy
The genus ''Ducula'' was introduced in 1836 by the English naturalist
Brian Houghton Hodgson
Brian Houghton Hodgson (1 February 1800 or more likely 1801 – 23 May 1894) was a pioneer naturalist and ethnologist working in India and Nepal where he was a British Resident. He described numerous species of birds and mammals from the Hima ...
with ''Ducula insignis'' as the
type species
In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...
. This taxon is now considered as a
subspecies of the
mountain imperial pigeon (''Ducula badia'').
The genus name ''Ducula'' is from the Latin ''dux'' genitive ''ducis'' meaning "leader".
The taxonomy of the imperial pigeon is unresolved, with the number of species within the genus ''Ducula'' reported variably as 34
and 36.
Derek Goodwin's 1959 paper on the taxonomy of the genus ''Ducula''
divides his arrangement of 36 species into 7 subgroups according to distribution and phenotype. This classification is followed by Gibbs et al.,
and followed here.
Species
The genus contains 41 species:
[
A new extinct species was described in a 2020 study of prehistoric avifaunas from the Kingdom of Tonga:
* Shutler's fruit pigeon (''Ducula shutleri'' Worthy & Burley sp. nov.)
]
Description
''Poliocephala'' species-group
Four species of imperial pigeon are found in Philippines
The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no),
* bik, Republika kan Filipinas
* ceb, Republika sa Pilipinas
* cbk, República de Filipinas
* hil, Republ ...
and Sulawesi. All have a distinct pale band across the centre of the tail, and a rich green or purple dorsum. This grouping shares characteristics and distribution with ''Ptilinopus'', and forms a link between the genera. The pink-belled ('' D. poliocephala'') and the white-bellied ('' D. forsteni'') imperial pigeon are similar and allopatric species. The Mindoro ('' D. mindorensis'') and the grey-headed ('' D. radiata'') imperial pigeons differ in size but are otherwise similar.
''Carola'' species-group
The spotted imperial pigeon ('' D. carola'') is sympatric to ''D. poliocephala'', and though smaller, short tailed and with spotted plumage, it is similar enough in appearance and distribution to suggest the taxa are related.
''Aenea'' species-group
This group's nominate species is the green imperial pigeon ('' D. aenea''), distinctive by its iridescent green, purple or bronze upper-parts and wings. The species-group is widespread through the Asia-Pacific. It is further separated into subgroups by Goodwin.
* Three Asian species with iridescent green upper-parts, pink head and neck with normal sized ceres; ''D. aenea'', the elegant ('' D. concinna'') and the white-eyed or spectacled ('' D. perspicillata'') imperial pigeons.
* The ''pacifica'' subgroup of six species, similar to ''aenea'' but with enlarged ceres, and distributed throughout the Pacific. The Pacific ('' D. pacifica'') and the Micronesian ('' D. oceania'') imperial pigeons are similar allospecies, while the Polynesian ('' D. aurorae'') and Marquesan ('' D. galeata'') imperial pigeons are larger birds with dark plumage. The red-knobbed imperial pigeon ('' D. rubricera'') and the spice imperial pigeon ('' D. myristicivora'') are similar but found in Melanesia
Melanesia (, ) is a subregion of Oceania in the southwestern Pacific Ocean. It extends from Indonesia's New Guinea in the west to Fiji in the east, and includes the Arafura Sea.
The region includes the four independent countries of Fiji, Va ...
and New Guinea
New Guinea (; Hiri Motu: ''Niu Gini''; id, Papua, or , historically ) is the world's second-largest island with an area of . Located in Oceania in the southwestern Pacific Ocean, the island is separated from Australia by the wide Torr ...
.
* The ''finschii'' subgroup of four species which may be New Guinea representatives of '' D. aenea'' stock; the purple-tailed ('' D. rufigaster''), cinnamon-bellied ('' D. basilica'') and Finsch's imperial pigeons, which all inhabit offshore islands. The shining or rufescent imperial pigeon ('' D. chalconota'') occupies more elevated ranges on the New Guinea mainland.
* Another subgroup similar to ''aenea'', but with upper parts not iridescent and less well defined, is the pink-headed imperial pigeon ('' D. rosacea'') as the nominate species, the Christmas Island ('' D. whartoni''), the grey ('' D. pickeringii'') and the island ('' D. pistrinaria'') imperial pigeons.
''Brenchleyi'' species-group
Contains 4 subgroups of large dark chestnut-bellied pigeons.
* The chestnut-bellied imperial pigeon ('' D. brenchleyi'') is the nominate species with the Baker's ('' D. bakeri''), Peale's ('' D. latrans''), and New Caledonian ('' D. goliath'') imperial pigeons, being allopatric through the Western Pacific islands.
* The Pinon imperial pigeon ('' D. pinon'') is found in New Guinea and its islands.
* The collared imperial pigeon ('' D. mullerii'') is found in New Guinea and Aru and has a distinctive dark collar.
* The Bismarck imperial pigeon ('' D. melanochroa'') is found on the Bismarck Archipelago.
Zoe's imperial pigeon
'' D. zoeae'' of Indonesia and New Guinea, is sufficiently distinct in colour to be placed in a species-group of its own.
''Badia'' species group
* The mountain ('' D. badia'') and the dark-backed ('' D. lacernulata'') imperial pigeons have a widespread distribution, the former from Indian subcontinent
The Indian subcontinent is a list of the physiographic regions of the world, physiographical region in United Nations geoscheme for Asia#Southern Asia, Southern Asia. It is situated on the Indian Plate, projecting southwards into the Indian O ...
to south China and Malaysia
Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...
, and the latter in southern Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
.
* The Timor imperial pigeon ('' D. cineracea'') is a similar grey pigeon, but found in Timor
Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is divided between the sovereign states of East Timor on the eastern part and Indonesia on the western part. The Indonesian part, also ...
.
''Bicolor'' species-group
The pied imperial pigeons form a discrete group of large white pigeons with black wingtips, found in New Guinea and its islands, and northern Australia. Goodwin recognised three species; the pied ('' D. bicolor'') the white ('' D. luctuosa'') and the Torresian ('' D. spilorrhoa''). The three allopatric species are closely related and subsequent authors have challenged this ranking, Johnstone including all three in a single species. Gibbs et al. group ''D. bicolor'' and ''D. spilorrhoa'' together, but adds the yellow-tinted imperial pigeon ('' D. subflavescens'') as another species. Frith includes ''D. subflavescens'' as a race of ''D. spilorrhoa''. Sibley and Monroe (1990) follow Goodwin.
The difficulty in assigning or removing species rank is compounded by the lack of data on behaviour and breeding patterns of the taxa. Similar species are allopatric, and there is no data on whether the species freely interbreed or not. Data on voice and behaviour is similarly poor.
The confusion is not helped by English naming. ''D. bicolor'' is variously described as the nutmeg pigeon, the Torres Strait pigeon, and the pied imperial pigeon. ''D. spilorrhoa'' is also described as the nutmeg pigeon, the white nutmeg pigeon, the Australian pied pigeon, the Australian pied imperial pigeon, the Torres Strait pigeon or the Torresian imperial pigeon.
Distribution and habitat
Imperial pigeons are only found in southern Asia, Australia, New Guinea and the Pacific, a distribution from the Himalayas (''D. badia'') to Tahiti in the South Pacific (''D. aurorare''). The greatest diversity of birds is in New Guinea. Imperial pigeons are strong fliers, are capable of flight over oceans, and have been successful in colonising islands and archipelagos.
Australia has a poor representation of ''Ducula'' amongst its fauna, with only one species breeding on the mainland (''D. spilorrhoa''). There is no clear explanation why more species of Ducula did not cross the Torres Strait islands to reach mainland Australia. The genus '' Lopholaimus'', comprising only one species may have been well represented on the Australian mainland before European settlement, thus excluding ''Ducula''.
Imperial pigeons are arboreal, and found almost exclusively in forest and woodland habitats where there is availability of fruit bearing trees. About half of the species occupy mountainous forest to elevations of 2500m. Many are found on islands, and live in coastal forests, with a few species inhabiting forest edges or mangroves.
Appearance
Tropical species of pigeons can display a rich variety of colour, presumably to facilitate species recognition. The plumage of the seed-eating genera of Columbidae is more often dull brown or grey. Typically imperial pigeons have dark dorsum and wings, ranging from grey to iridescent green. Their breasts are paler, ranging in colour from grey through orange and pink to dark grey. Less conspicuous markings are found on birds isolated to islands. Most species display little or no sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...
.
Imperial pigeons are large to very large pigeons; typical length is 35 to 45 cm, and they have medium to long tails. The critically endangered Marquesan imperial pigeon is 50 cm long and is the largest arboreal pigeon in the family Columbidae.
Fat quills are present in ''D. bicolor'' and ''D. spilorrhoa''. Fat quills are modified feathers that produce a lipoid substance that is used in a similar way to the secretions of the preen gland. Fat quills are found around the rump of ''D. bicolor'' and in other Columbidae species. Preening with the yellow coloured lipid causes variations in colour of the head and shoulders of ''D. bicolor'', ranging from cream to yellow. Colouration differs between individuals and the stage of molt, deeper colouring found just prior to molt, leading to some confusion in identifying taxa. The function of the fat quills is debatable, with suggestions of a sexual signal, an antibacterial, or as an olfactory signal. Yellow lipoid substance can be expressed from the base of a broken rachis
Behaviour
There is a paucity of information on most species of ''Ducula'', many of which are shy and live in remote areas, making observation difficult. Breeding and nesting behaviour of species has been poorly documented. Though large and numerous, birds can be inconspicuous, feeding quietly in deep foliage.
''Ducula'' are highly mobile and can travel large distances to find fruit. They are strong fliers and able to fly between islands to exploit erratic food sources. Small islands whose flora would be unable to sustain a long term population can provide a temporary food source for nomadic birds. Crome has documented daily flights of more than 32 km from island roosts to the mainland.
Some species live singly or in pairs, but many are highly social, forming flocks of 30 to 50 birds. Pied imperial pigeons favour off shore islands or mangroves for breeding sites. ''D. spilorrhoa'' forms large colonies on the Queensland coast, flying to fruit bearing forests during the day and roosting together at night. Low Isles in North Queensland hosted 20,000 to 25,000 birds in the 1971-1973 breeding seasons. A volunteer based count in December 2014 reported a similar number of over 22,000 pied imperial pigeons
pipwatch.net
. An anecdotal report from 1908 describes flocks of 100,000 ''D. spilorrhoa'' flying from the mainland to their roosting sites on Dunk Island, North Queensland.
Pigeons drink by a pumping or sucking mechanism that allows them to drink with their beak continuously immersed in water. Fruit eating pigeons may utilize water from their diet and have less water requirements than other pigeons.
Diet
Imperial pigeons are arboreal, living in forests and mangroves that can supply seasonal fruit from tropical trees, palms, vines and bushes. Most birds clamber through twigs and branches of canopy, leaning or hanging upside down to reach fruit. Fruit is twisted off stems with their bill and swallowed whole. They are able to extend their gapes to 40mm in order to swallow large fruits. ''D. galeata'' can swallow seeds of 70mm. Their diet can be supplemented with flowers, leaves and insects.
In contrast to seed-eating pigeons, ''Ducula'' have thin-walled gizzards and short wide guts, allowing large seeds to pass through. After digesting the fleshy parts, they void the seeds intact, thus playing an important role as seed dispersers.
Other genera of Columbidae have grinding gizzard
The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ found in the digestive tract of some animals, including archosaurs (pterosaurs, crocodiles, alligators, dinosaurs, birds), earthworms, some gastropods, so ...
s which either destroy seeds, or regurgitate larger seeds. Some large seeded fruits are eaten by both Nicobar pigeon
The Nicobar pigeon (''Caloenas nicobarica'', Car: ') is a bird found on small islands and in coastal regions from the Andaman and Nicobar Islands, India, east through the Malay Archipelago, to the Solomons and Palau. It is the only living membe ...
s (''Colaenesa nicobarica'') and imperial pigeons, with the former destroying seeds and the latter excreting them intact .
Imperial pigeons are amongst the largest frugivores in the forest, and can disperse seeds from fruit too large for most other species to handle. A fruit size of 30 mm would exclude all vertebrates other than hornbills (''Bucerotidae
Hornbills (Bucerotidae) are a family of bird found in tropical and subtropical Africa, Asia and Melanesia. They are characterized by a long, down-curved bill which is frequently brightly coloured and sometimes has a casque on the upper mandibl ...
'') and ''Ducula''. Medium-sized pigeons tend to feed on medium-sized fruit, while larger pigeons feed on larger fruit. Pacific pigeons (''D. pacifica'') are shown to be excellent seed dispersers in Tonga
Tonga (, ; ), officially the Kingdom of Tonga ( to, Puleʻanga Fakatuʻi ʻo Tonga), is a Polynesian country and archipelago. The country has 171 islands – of which 45 are inhabited. Its total surface area is about , scattered over in ...
and are thus critical in the management of forests throughout their habitat.
Reproduction
Imperial pigeons construct somewhat flimsy nests of loosely woven twigs placed in the fork of a tree. Species that roost in mangroves construct more substantial nests from mangrove shoots. They generally lay a single egg with a relatively short incubation period. Both sexes share incubation and care of nestlings. ''Ducula'', typical of most pigeons, produce a nutritiously rich crop milk
Crop milk is a secretion from the lining of the crop of parent birds that is regurgitated to young birds. It is found among all pigeons and doves where it is referred to as pigeon milk. An analog to crop milk is also secreted from the esopha ...
which allows the chicks to rapidly fledge and leave the nest, reducing their period of vulnerability. The breeding cycle is short, allowing several broods to be reared in succession over an extended summer breeding season.
Crop milk
Crop milk is a secretion from the lining of the crop of parent birds that is regurgitated to young birds. It is found among all pigeons and doves where it is referred to as pigeon milk. An analog to crop milk is also secreted from the esopha ...
is a thick cheesy substance, derived from squamous cells sloughed off from the crop of both male and female pigeons which promotes a high growth rate in squabs. There are no studies of the composition of crop milk specific to ''Ducula''. However, in domestic pigeons (''Columba livia''), the crop milk is found to contain lipids, proteins and enzymes, and also facilitates the transfer of maternal antibodies to squabs, as in mammals. The hypertrophy of crop tissue and production of crop milk is determined by the hormone prolactin, as in mammals.
An abundance of fruit is important to the breeding success of frugivorous birds. Large breeding colonies require unexploited forest to provide fruit bearing trees for daily feeding.
Voice
Variable between species, but ranging from typical 'coo' and 'coo-woo' of other pigeon families, to resonant 'whoops', abrupt booming calls or barking notes, to disyllabic deep booming calls.
Migration
Columbidae are generally strong fliers and effective colonisers, being able to make across ocean flights to access seasonal fruit supplies. ''D. bicolor'' is partly migratory, its distribution changing according to food availability.
Ecology and conservation
About one third of extant pigeons in the family Columbidae are endangered to a greater or lesser degree, making the family one of the most threatened in the world. Asia, Australasia and Oceania are home to nearly two-thirds of extant species of Columbidae, but three quarters of those species are threatened.
The greatest threats to Columbidae species is habitat loss and degradation, hunting by man, and alien predators. Other threats include disease and possible competition from introduced species. Large flocks of Ducula are mobile and able to exploit large areas for food sources, but are nevertheless vulnerable to large scale loss of forests.
Pigeons are exploited by man for food and sport. Hunting of ''D. spillorhoa'' on the Australian mainland has reduced populations. Hunting for food remains a problem in Asia and the Pacific as Columbidae provides a palatable source of protein. Historically, human habitation has been associated with extinctions.
Many species of ''Ducula'' live on forested islands in the Indian Ocean, SE Asian archipelagos and on Pacific and Australasian islands. Island species are particularly vulnerable as highly specialised populations, ill-prepared for introduced predators such as cats, rats and stoat
The stoat (''Mustela erminea''), also known as the Eurasian ermine, Beringian ermine and ermine, is a mustelid native to Eurasia and the northern portions of North America. Because of its wide circumpolar distribution, it is listed as Least Conc ...
s.
One of the most threatened species of ''Ducula'' is the Marquesan imperial pigeon
The Marquesan imperial pigeon (''Ducula galeata''), also known as the Nukuhiva pigeon or Upe, is a pigeon which is endemic to Nuku Hiva in the Marquesas Islands of French Polynesia. This pigeon is only found in some valleys in the western part of ...
(''D. galeata'') whose numbers have been reduced from 250 individuals in 1998 to fewer than 100 birds in 2000. A translocation programme has been initiated, increasing the number of islands in which ''D. galeata'' has a breeding colony.
Frugivorous pigeons play an important role in seed dispersal and the preservation of tropical forest diversity. Population loss may have a detrimental effect on fauna of a regions, especially when deforestation by logging leaves large cleared areas needing rehabilitation.
References
External links
*
{{Authority control
Ptilinopinae
Taxonomy articles created by Polbot
Bird genera
Taxa named by Brian Houghton Hodgson