Ducula whartoni

Taxonomy

Assessment Information

Geographic Range

Population

Habitat and Ecology

Threats

Conservation Actions

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Taxonomy [top]

Kingdom	Phylum	Class	Order	Family
ANIMALIA	CHORDATA	AVES	COLUMBIFORMES	COLUMBIDAE

Scientific Name:

Ducula whartoni

Species Authority:

(Sharpe, 1887)

Common Name/s:

English

–

Christmas Imperial Pigeon, Christmas Island Imperial-pigeon, Christmas Island Imperial Pigeon, Christmas Island Imperial-Pigeon

Assessment Information [top]

Red List Category & Criteria:

Vulnerable D2 ver 3.1

Year Assessed:

2008

Assessor/s:

BirdLife International

Reviewer/s:

Garnett, S., Taylor, J., Butchart, S.

Contributor/s:

Hennicke, J., Blyth, J., Low, T., O'Dowd, D., Green, P., Garnett, S., James, D.

Justification:
This species is listed as Vulnerable because it has a moderately small population in a very small range on one very small island, where it remains susceptible to invasive species and stochastic events.

History:

2006	–	Vulnerable
2004	–	Vulnerable
2000	–	Critically Endangered
1996	–	Vulnerable
1994	–	Vulnerable

Geographic Range [top]

Range Description:	Ducula whartoni is endemic to Christmas Island (to Australia), in the Indian Ocean. Numbers have apparently fluctuated, and perhaps declined, between the time of the island's settlement in 1888 and the mid-1970s, but no good data are available. In 1975, the population was estimated at 10-100 breeding pairs. The breeding population was estimated at c.1,000 mature individuals in 2000. However, it is widespread and considered very common on the island, and the total population probably exceeds this estimate by at least an order of magnitude⁸. This is supported by surveys in 2005 and 2006, in which the species was recorded during 92% of point counts and at 98% of surveyed sites⁹. At the end of the 19th century, it was unsuccessfully introduced to Cocos-Keeling Islands (to Australia). It occupies a range of no more than 137 km² ⁸.
Countries:	Native: Christmas Island
Range Map:	Click here to open the map viewer and explore range.

Population [top]

Population:	The breeding population has been estimated at c.1,000 mature individuals (Garnett and Crowley 2000). However, it is widespread and considered very common on the island, and the total population probably exceeds this estimate by at least an order of magnitude (D. James in litt. 2007).
Population Trend:	Stable

Habitat and Ecology [top]

Habitat and Ecology:	It is found in rainforest and, to some extent, in secondary regrowth dominated by the introduced Japanese cherry Muntingia calabura. Surveys in 2005 and 2006 found the species to be more common in evergreen forest than in either semi-deciduous forest or cleared areas⁹. It nests in the top of rainforest trees and other dense vegetation, and feeds on native and exotic fruits, as well as buds and leaves.
Systems:	Terrestrial

Habitat and Ecology:

It is found in rainforest and, to some extent, in secondary regrowth dominated by the introduced Japanese cherry Muntingia calabura. Surveys in 2005 and 2006 found the species to be more common in evergreen forest than in either semi-deciduous forest or cleared areas⁹. It nests in the top of rainforest trees and other dense vegetation, and feeds on native and exotic fruits, as well as buds and leaves.

Systems:

Terrestrial

Threats [top]

Major Threat(s):	About one third of the species's previously favoured plateau forest was cleared for phosphate mining before clearance ceased in 1987. This loss has been partly offset by the introduction of M. calabura, which flourishes on many former mine fields and other disturbed areas, and provides a rich food source for much of the year. Future habitat loss is possible through clearance for mining². In 2007, significant patches of mature secondary forest were cleared for mining⁸. Also in 2007, a new application to mine a 250 ha area of rainforest³ was turned down⁴. However, this has subsequently gone to appeal⁸. Illegal hunting continued after prohibition in 1977, but is now less prevalent. The failure of the introduction to Cocos-Keeling Islands has been attributed to hunting and/or lack of suitable food-trees. A possible threat is the introduced yellow crazy ant Anoplolepis gracilipes, which formed super-colonies during the 1990s and spread rapidly to cover about 25% of Christmas Island or about 3,400 ha, but was controlled over about 2,900 ha in September 2002. Once controlled, however, the ants are re-establishing supercolonies⁸. In 2006, the ants were regarded as widespread and patchily common⁵. If allowed to spread uncontrolled, ant super-colonies may prey directly on nestlings, although there is no evidence that this is a threat to the overall population, and alter island ecology by killing the dominant life-form, the red crab Gecaroidea natalis, which otherwise inhibits understorey plant growth and the spread of weeds by eating the seeds and seedlings of both native and invasive species^1,2,8. The ants also farm scale insects, causing canopy die-back, which in turn promotes weed growth and further alters forest structure⁸. The scale at which these processes occur is uncertain⁸.

Major Threat(s):

About one third of the species's previously favoured plateau forest was cleared for phosphate mining before clearance ceased in 1987. This loss has been partly offset by the introduction of M. calabura, which flourishes on many former mine fields and other disturbed areas, and provides a rich food source for much of the year. Future habitat loss is possible through clearance for mining². In 2007, significant patches of mature secondary forest were cleared for mining⁸. Also in 2007, a new application to mine a 250 ha area of rainforest³ was turned down⁴. However, this has subsequently gone to appeal⁸. Illegal hunting continued after prohibition in 1977, but is now less prevalent. The failure of the introduction to Cocos-Keeling Islands has been attributed to hunting and/or lack of suitable food-trees. A possible threat is the introduced yellow crazy ant Anoplolepis gracilipes, which formed super-colonies during the 1990s and spread rapidly to cover about 25% of Christmas Island or about 3,400 ha, but was controlled over about 2,900 ha in September 2002. Once controlled, however, the ants are re-establishing supercolonies⁸. In 2006, the ants were regarded as widespread and patchily common⁵. If allowed to spread uncontrolled, ant super-colonies may prey directly on nestlings, although there is no evidence that this is a threat to the overall population, and alter island ecology by killing the dominant life-form, the red crab Gecaroidea natalis, which otherwise inhibits understorey plant growth and the spread of weeds by eating the seeds and seedlings of both native and invasive species^1,2,8. The ants also farm scale insects, causing canopy die-back, which in turn promotes weed growth and further alters forest structure⁸. The scale at which these processes occur is uncertain⁸.

Conservation Actions [top]

Conservation Actions:	Conservation Actions Underway The Christmas Island National Park was established in 1980, and has since been extended to cover more than 60% of the island⁸. A control programme for A. gracilipes has been successfully initiated since 2000 and effectively eliminated the ant from 2,800 ha of forest (95% of its former extent)¹. Monitoring of the problem continues and hand-baiting measures have been ongoing. Aerial baiting was carried out in September 2002 and proved to be successful against major colonies⁶, with 98% of ants controlled⁸. However, the ants have since recovered⁸. The ants remained persistent in 2006, and perpetual baiting may be the only means of controlling them⁵. The bait used so far is known to be toxic to invertebrates, including crabs, and although alternatives have been trialled, an effective replacement has not been found⁸. Control of the scale bugs that the ants tend for their sugar secretions has been suggested, in order to reduce this food supply^5,8. Control of the ants may have allowed the species's population to stabilise⁷. Conservation Actions Proposed Monitor population trends through standardised surveys. Continue to investigate the potential impacts of A. gracilipes on the species. Control the abundance and spread of A. gracilipes.

Conservation Actions:

Conservation Actions Underway
The Christmas Island National Park was established in 1980, and has since been extended to cover more than 60% of the island⁸. A control programme for A. gracilipes has been successfully initiated since 2000 and effectively eliminated the ant from 2,800 ha of forest (95% of its former extent)¹. Monitoring of the problem continues and hand-baiting measures have been ongoing. Aerial baiting was carried out in September 2002 and proved to be successful against major colonies⁶, with 98% of ants controlled⁸. However, the ants have since recovered⁸. The ants remained persistent in 2006, and perpetual baiting may be the only means of controlling them⁵. The bait used so far is known to be toxic to invertebrates, including crabs, and although alternatives have been trialled, an effective replacement has not been found⁸. Control of the scale bugs that the ants tend for their sugar secretions has been suggested, in order to reduce this food supply^5,8. Control of the ants may have allowed the species's population to stabilise⁷.

Conservation Actions Proposed
Monitor population trends through standardised surveys. Continue to investigate the potential impacts of A. gracilipes on the species. Control the abundance and spread of A. gracilipes.

Citation:	BirdLife International 2008. Ducula whartoni. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. <www.iucnredlist.org>. Downloaded on 08 February 2012.
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