Archived 2011-2012 topics: Ribbon-tailed Drongo (Dicrurus megarhynchus): uplist to Near Threatened?

Initial deadline for comments: 31 January 2012 [note that this has been moved back by about two months].

BirdLife species factsheet for Ribbon-tailed Drongo

Ribbon-tailed Drongo Dicrurus megarhynchus is endemic to New Ireland (Papua New Guinea), where it is found in primary lowland forest, hill forest, stunted mossy montane forest and tall secondary growth from sea-level to c.1,800 m (del Hoyo et al. 2009). It is listed as Least Concern on the basis that it was not thought to approach the thresholds for Vulnerable under any of the IUCN criteria.

Although this species has a restricted range, it was not believed to approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence [EOO] of less than 20,000 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 trend was not known, but the population was not believed to be decreasing sufficiently rapidly to approach the thresholds under the population trend criterion (at least a 30% decline over ten years or three generations). The population size has not been quantified, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (fewer than 10,000 mature individuals with a continuing decline estimated to be at least 10% over ten years or three generations, or with a specified population structure).

Mapping of the species’s range by BirdLife indicates that it has an EOO of only c.7,000 km2, which meets the range size threshold for Vulnerable under criterion B1; however, formerly there was uncertainty over the trends in its distribution and population. A recently published analysis of forest loss in Papua New Guinea indicates that c.21% of forest cover was lost in New Ireland between 1972 and 2002, with over half of that loss attributed to logging, and clearance for subsistence agriculture also having a marked impact (Shearman et al. 2009). Of New Ireland’s total forest cover in 1972, c.32% had been degraded by 2002, leaving c.40% of remaining forest cover in a degraded state (Shearman et al. 2009). Thus there is evidence that the species’s habitat is being destroyed and degraded, leading to on-going declines in the Area of Occupancy (AOO) and area, extent and/or quality of suitable habitat. However, the species is unlikely to qualify for uplisting to Vulnerable under criterion B1 because there is currently no evidence to suggest that its habitat is severely fragmented, i.e. more than 50% in patches too small to support viable populations, and the species is considered to occur at more than 10 locations because of the localised impact of the processes and events driving deforestation and forest degradation.

It is therefore proposed that the species be uplisted to Near Threatened (NT) under criterion B1a+b(ii,iii). The species is unlikely to qualify as NT under criterion A because the rate of deforestation on New Ireland suggests that the rate of population decline over 10 years does not approach the threshold for Vulnerable (typically 20-29% over 10 years for NT species). Comments are invited on the proposal to uplist this species to Near Threatened under citerion B1a+b(ii,iii) and additional information is requested, including data on its population size and density.

References:

del Hoyo, J., Elliott, A. and Christie, D. (eds.) (2009) Handbook of the Birds of the World, Vol. 14: Bush-shrikes to Old World Sparrows. Barcelona, Spain: Lynx Ediciones.

Shearman, P. L., Ash, J., Mackey, B. Bryan, J. E. and Lokes, B. (2009) Forest Conversion and Degradation in Papua New Guinea 1972-2002. Biotropica 41: 379-390.

Related posts:

  1. Archived 2010-2011 topics: Tablas Drongo (Dicrurus menagei): list as Endangered?
  2. Archived 2011-2012 topics: Watkins’s Antpitta (Grallaria watkinsi): uplist to Near Threatened?
  3. Archived 2011-2012 topics: Knobbed Hornbill (Aceros cassidix) and Sulawesi Hornbill (Penelopides exarhatus): uplist to Near Threatened?
  4. Archived 2011-2012 topics: The effects of projected climate change on the Southern Ocean and Antarctic environment: uplist Emperor Penguin (Aptenodytes forsteri) to Vulnerable and Adelie Penguin (Pygoscelis adeliae) to Near Threatened?
  5. Archived 2010-2011 topics: White-tailed Laurel Pigeon (Columba junoniae): downlist to Near Threatened or Least Concern?
This entry was posted in Archive, Pacific and tagged . Bookmark the permalink.

3 Responses to Archived 2011-2012 topics: Ribbon-tailed Drongo (Dicrurus megarhynchus): uplist to Near Threatened?

  1. Guy Dutson says:

    I suggest that >50% population is in the contiguous tract of montane forest which extends down into the lowlands of southern NI. I have only visited a handful of sites in NI, where the species appeared to occur in closed secondary forest but not open degraded forest.

  2. I have twice surveyed rainforest birds in New Ireland (1976 and 1993) and in both instances, Dicrurus megarhynchus was uncommon in old growth forest. As Guy Dutson notes in an earlier comment, the species does have a rather large block of contiguous hill and montane forest in the southern ‘bulb’ of New Ireland, although I am told that the lowland and hill forests of the north are being heavily degraded and in some instance converted.

  3. Joe Taylor says:

    The following comment is posted on behalf of Guy Dutson:

    I estimate the population size to be in the hundreds of thousands, based on encounter rates of 4 during 14 hours in logged and degraded lowland forest, 14 during 7 hours in degraded hill forest, and 67 during 26 hours in primary submontane forest, assuming an encounter rate of 2 per hour roughly equates to one per hectare (extrapolating from encounter rates and published densities for Spangled Drongo in Australia and New Guinea), and published estimates of c.387,000 ha primary forest and c.259,000 ha degraded forest on New Ireland in 2002 (Shearman et al. 2009).

Comments are closed.