This discussion was first published as part of the 2013 Red List update, but remains open for comment to enable reassessment in 2015.
Black-throated Shrikebill Clytorhynchus nigrogularis is found on the Fijian islands of Viti Levu, Vanua Levu, Taveuni, Kadavu and Ovalau (Pratt et al. 1987). It is currently listed as Vulnerable under criterion C1 on the basis that it has a small population of fewer than 10,000 mature individuals, which was thought to have an estimated continuing decline of at least 10% over three generations (c.13 years in this species), owing to losses of mature old-growth forest through continued logging and forest conversion. However, according to the Department of Forestry, the logging rate is slowing.
Recent surveys on Fiji have generated much more data on this species, showing it to be widespread but existing at low population densities (c.1 bird/km2 on average). The species was recorded at 55% of the sites surveyed (19/34 sites) which were pre-selected as the densest, wettest old-growth forest. Very few were recorded in logged or degraded forest. If it is assumed to occur in 50% of the forest, which covers about 40% of the species’ Extent of Occurrence (EOO) (c.17,500 km2), the total population is likely to be in the range of 2,500-9,999 birds (G. Dutson in litt. 2005). This equates to 1,667-6,666 mature individuals, rounded here to 1,500-7,000 mature individuals (not 3,750-14,999 individuals, rounded to 3,500-15,000 individuals, as stated in the factsheet). Given the species’s intolerance of habitat degradation, it is likely to be declining at the same rate as forest loss and degradation, which is estimated to be about 0.5-0.8% per year (Claasen 1991). Thus, the population is inferred to be declining by 6.5-10% over c.13 years (three generations). If this is confirmed, the species would no longer qualify as Vulnerable under C1. Since the EOO of this species is estimated at c.16,900 km2, it has a patchy distribution and the extent and quality of habitat, Area of Occupancy (AOO) and number of mature individuals are thought to be in continuing decline, this species may warrant downlisting to Near Threatened under criterion B1ab(ii,iii,v), on the basis that it approaches the thresholds for Vulnerable. If there is sufficient evidence to suggest that all subpopulations approach as few as 1,000 mature individuals, this species would also qualify as Near Threatened under criterion C2a(i) of the IUCN Red List.
For the purposes of Red List assessments, subpopulations are defined as geographically or otherwise distinct groups between which there is little or no demographic or genetic exchange, i.e. typically one successful migrant per year or less.
Further information is requested on this species’s population trends, distribution and size of the largest subpopulation. Comments on its proposed downlisting are welcome.
Claasen, D. R. (1991) Deforestation in Fiji: National environment management plan report 2.
Pratt, H. D., Bruner, P. L. and Berrett, D. G. (1987) A field guide to the birds of Hawaii and the tropical Pacific. Princeton, NJ: Princeton University Press.