Imperial pigeon

Ducula is a major 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 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. They have large gapes and swallow seeds whole, playing an important role in seed dispersal. Imperial pigeons are found in forests of southern Asia, New Guinea, 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. 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. Four species of imperial pigeon are found in Philippines 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. 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. 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. a) 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. b) 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 and New Guinea.