LC
Violaceous Coucal Centropus violaceus



Justification

Justification of Red List Category
This species has a very large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km² or Area of Occupancy <2,000 km² combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population size may be small, but the species is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). For these reasons the species is evaluated as Least Concern.

Population justification
It is widely distributed on both range islands, but occurs at low densities (Erritzøe et al. 2012), and is more common on New Britain than on New Ireland. The population density is thought to be below 0.1 pairs per km2 (Mayr and Diamond 2001).

The population size has been previously estimated to be greater than 10,000 individuals (Buchanan et al. 2008, Davis et al. 2018), which roughly equates to 6,700 mature individuals. Based on a minimum density of 0.3 individuals per km2 (based on the pair density estimate from Mayr and Diamond 2001), a maximum density derived from the first quartile population density estimate from congeners (2.65 individuals per km2), the projected area of tree cover within the range in 2021 (c. 34,300 km2; Global Forest Watch 2021), and assuming the tree cover to be 75-100% occupied, the population size may be tentatively suspected to fall within the range 7,000 - 91,000 individuals, roughly equating to 5,000 - 61,000 mature individuals. Taking into account the previously estimated minimum population size (Buchanan et al. 2008, Davis et al. 2018), the population size is here placed in the band 6,700 - 61,000 mature individuals.

Approximately 80% of the available habitat is on New Britain. Assuming each island holds a single subpopulation, the largest subpopulation may hold approximately 4,000 - 50,000 mature individuals.

Trend justification
The species is inferred to be declining owing to ongoing clearance of lowland forest (Buchanan et al. 2008, Global Forest Watch 2021). Buchanan et al. (2008) calculated the rate of forest loss within the species's range on New Britain as 12.4% over 1990-2000.

Over 18 years (three generations) from 2002-2020, approximately 9% of tree cover with at least 50% canopy cover was lost from within the species's range (Global Forest Watch 2021). Based on this data, it is suspected that 10-13% will be lost over the next three generations.

This species is dependent on forest, but it appears to be more tolerant of forest degradation than previously thought (Davis et al. 2018). The species's population size is therefore suspected to have undergone a reduction of 1-14% over the past three generations, and is suspected to undergo a reduction of 1-18% over the next three generations.

Distribution and population

Centropus violaceus is endemic to the islands of New Britain and New Ireland in the Bismarck Archipelago, Papua New Guinea where although it is rather poorly known, it appears to be widely distributed and not uncommon in suitable habitat. 

Ecology

It inhabits lowland rainforest, including primary forest and disturbed habitat (Payne 2005, Davis et al. 2018). It was found to be equally common in primary and degraded forest on New Britain (R. Davis in litt. 2021). It has been recorded up to c.1,370 m in the Nakanai mountains (Erritzøe et al. 2012), but is usually found in lowland forest up to c. 760 m (Bishop and Jones 2001). It feeds on large insects, snails and small frogs (Gillard and Lecroy 1967). It breeds from November to January.

Threats

It is threatened by logging and forest conversion, particularly for conversion to oil palm plantations. 

In 2002, all forest in New Ireland and West New Britain was allocated for industrial forestry, and New Britain alone accounted for approximately half of Papua New Guinea's timber exports (Bun et al. 2004). Regulations on the frequency of re-logging areas are being ignored (Nelson et al. 2014). 

Many areas of lowland forest in New Britain have been converted to oil palm plantations (Swartzendruber 1993, Buchanan et al. 2008). Much of the Bismarck Archipelago has been allocated as Special Agricultural Business Lease (SABL) areas, which would permit conversion to oil palm plantations. However, many of these areas appear to be unsuitable for oil palm, suggesting that they may be in place to facilitate commercial logging, under the pretext of oil palm development (Nelson et al. 2014, Bryan et al. 2015). Nevertheless, conversion to oil palm is likely to continue slowly in the region (Nelson et al. 2014).

Around 12% of forest cover in New Britain was lost between 1989 and 2000, with over 20% lost in the lowlands below 100 m (Buchanan et al. 2008). Since then, the rate of deforestation apparently slowed (B. Beehler in litt. 2016), and between 2002 and 2014, around 7.4% of forest on New Britain and 7.6% of forest on New Ireland was logged or cleared (Bryan et al. 2015). On New Ireland, most lowland forest was lost before 1989, and the area converted to oil palm has been much smaller (Davis et al. 2018).

Conservation actions

Conservation Actions Underway
Several bird surveys have taken place on New Britain and New Ireland. No conservation measures are known to have been taken.

Conservation Actions Proposed
Carry out surveys across its range to estimate population density and gain a better estimate of its population size. Continue to monitor trends in forest loss in the region.

Identify and effectively protect a network of reserves, including some containing large areas of unlogged lowland forest and some large community-based conservation areas.

Identification

64cm. A very large coucal, entirely blackish with a violet sheen. Red iris and black eye-ring surround by whitish bare skin. Black bill and legs and feet variously whitish, light brown or slaty blue. Similar ssp. None within range. Voice Deep disyllabic wu-wuuu with longer, louder second note, similar to a large sheet of metal being flexed, repeated at variable intervals. Sometimes interspersed with rapid, deep gulps. Very deep, hoarse rasping wrah!-wrah!

Acknowledgements

Text account compilers
Wheatley, H.

Contributors
Beehler, B.M., Bishop, K.D., Dutson, G., Wilkinson, R., Butchart, S., Ekstrom, J., Mahood, S., Derhé, M. & Davis, R. E.


Recommended citation
BirdLife International (2022) Species factsheet: Centropus violaceus. Downloaded from http://www.birdlife.org on 19/05/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 19/05/2022.