Both genera display brightly coloured plumage, predominantly green, often with contrasting under-parts of purple, orange or red.

[3] Imperial pigeons are found in forests of southern Asia, New Guinea, northern Australia and the Pacific islands.

[9][10] Derek Goodwin's 1959 paper on the taxonomy of the genus Ducula[9] divides his arrangement of 36 species into 7 subgroups according to distribution and phenotype.

[14] Gibbs et al. group D. bicolor and D. spilorrhoa together, but adds the yellow-tinted imperial pigeon (D. subflavescens) as another species.

[8] The difficulty in assigning or removing species rank is compounded by the lack of data on behaviour and breeding patterns of the taxa.

Imperial pigeons are strong fliers, are capable of flight over oceans, and have been successful in colonising islands and archipelagos.

[15] There is no clear explanation why more species of Ducula did not cross the Torres Strait islands to reach mainland Australia.

[2] Imperial pigeons are arboreal, and found almost exclusively in forest and woodland habitats where there is availability of fruit bearing trees.

Fat quills are modified feathers that produce a lipoid substance that is used in a similar way to the secretions of the preen gland.

[20] Yellow lipoid substance can be expressed from the base of a broken rachis [18] There is a paucity of information on most species of Ducula, many of which are shy and live in remote areas, making observation difficult.

Small islands whose flora would be unable to sustain a long term population can provide a temporary food source for nomadic birds.

D. spilorrhoa forms large colonies on the Queensland coast, flying to fruit bearing forests during the day and roosting together at night.

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.

[2] Imperial pigeons are arboreal, living in forests and mangroves that can supply seasonal fruit from tropical trees, palms, vines and bushes.

[17][24] In contrast to seed-eating pigeons, Ducula have thin-walled gizzards and short wide guts, allowing large seeds to pass through.

[2][23] Imperial pigeons are amongst the largest frugivores in the forest, and can disperse seeds from fruit too large for most other species to handle.

[30] Pacific pigeons (D. pacifica) are shown to be excellent seed dispersers in Tonga and are thus critical in the management of forests throughout their habitat.

[2] Ducula, typical of most pigeons, produce a nutritiously rich crop milk which allows the chicks to rapidly fledge and leave the nest, reducing their period of vulnerability.

However, in domestic pigeons (Columba livia), the crop milk is found to contain lipids, proteins and enzymes,[31] and also facilitates the transfer of maternal antibodies to squabs, as in mammals.

Large breeding colonies require unexploited forest to provide fruit bearing trees for daily feeding.

[33] Columbidae are generally strong fliers and effective colonisers, being able to make across ocean flights to access seasonal fruit supplies.

Island species are particularly vulnerable as highly specialised populations, ill-prepared for introduced predators such as cats, rats and stoats.

[35] One of the most threatened species of Ducula is the Marquesan imperial pigeon (D. galeata) whose numbers have been reduced from 250 individuals in 1998 to fewer than 100 birds in 2000.

[17] Frugivorous pigeons play an important role in seed dispersal and the preservation of tropical forest diversity.

[4][28] Population loss may have a detrimental effect on fauna of a region, especially when deforestation by logging leaves large cleared areas needing rehabilitation.