The Pacific Imperial-pigeon is the most frequently observed of the three species. It is a large, grey pigeon with dark, glossy green/black wings and back and a rufous undertail. When seen close its diagnostic feature is the black cere (lump) on top, and at the base, of its bill. Its distribution is unusual, being typically found on small islands within the Solomons and Fiji, it occurs on all the islands of Vanuatu, and again from Tonga to Western Samoa and Cook Islands. Although large it is quite secretive, but gives itself away by a distinctive purr call, given at intervals. It also has a coo call that is repeated every 10-15 seconds, which makes it relatively easy for a skilled hunter to locate. It is a sought-after food item in most countries where it occurs – it has been estimated that over 20,000 pigeons are shot and consumed, per year, in Samoa. Despite this the species is considered to be of Least Concern, in the IUCN Red List of Globally Threatened species.
The second species of Imperial-pigeon on Vanuatu, known as the Vanuatu, or Bakers, Imperial-Pigeon is restricted to the upland areas (above 300m) of Santo, Maewo, Ambae, Pentecost and Ambrym. It can also be found on the larger Banks Islands where it occurs down to sea-level. It differs from the Pacific Imperial-pigeon by being a much darker purple-chestnut on the underparts and having no cere on the bill. It has a deep powerful booming hoow – hoow – hoow call which is the characteristic sound in the upland areas where it resides. Not uncommon, but can be difficult to see especially in areas where it is hunted for food, this species is considered Vulnerable in the IUCN Red List.
The third species, the Metallic or White-throated Pigeon is from a different family of pigeons compared with the previous two species. It is another dark pigeon with a green, purple and blue gloss to its feathers – but with a distinctive white V across its throat. It is not uncommon, but not easy to locate as it calls much less frequently than the previous two species. Its call is a three note whoo – ooooooo – ooo, repeated four to five times in quick succession. It can certainly be a difficult bird to locate in areas with a lot of slingshots – I have undertaken more than 30 hours of bird surveying on Tongoa and not seen or heard a single individual. Yet I know, from the trail cameras around the site, that this species is present. The wide distribution of this species, which can be found from Papua New Guinea eastwards to Samoa, is reflected in the fact that it is considered of Least Concern in the IUCN Red List.
Imperial-pigeons are, along with fruit-doves, primarily arboreal fruit eaters, often nomadic, and strong flyers capable of colonising isolated islands. It is likely that they are the prime reason that fruiting trees are so prevalent in forests across the Pacific. Representatives of both taxa can be found as far east as the Marquesas or Pitcairn, absent only from Hawaii and Easter Island. Fruit is a poor food for growing birds, and this diet was only possible because pigeons feed their chicks a ‘milk’ that is disgorged from the crop (part of the digestive tract) of both parents. This strong association with fruit can have its downsides. Several of the invasive species in the Pacific are fruit-bearing shrubs and trees that spread rapidly because the pigeons select them for food and then travel distances between consuming and excreting.
We still don’t understand why the Pacific Imperial-pigeon is a transient, small-island hopping species in the Solomons and Fiji, but the dominant species on the main islands of Vanuatu. A comparison of the diet and habitat requirements of the Vanuatu, the Barking (endemic pigeon of Fiji) and the Pacific Imperial-pigeons would be a fascinating study to try to unravel this conundrum.
By bird expert Dr Mark O’Brien, Regional Program Coordinator for BirdLife International.