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