This discussion was first published as part of the 2013 Red List update, but remains open for comment to enable reassessment in 2015.
Grey-banded Babbler Robsonius sorsogonensis is currently listed as Vulnerable under B1ab(ii,iii,v) because it has a small range, thought to be found at ten or fewer locations, and its habitat declining both in area and quality as a result of deforestation.
It is found in southern Luzon in the Philippines. However, recent data suggests that it may be present at more localities than previously thought. P. Hosner (in litt. 2012) gathered information on this species’s locality and reported that it is found at more than ten locations, including Sorsogon and Camarines Sur. It has also been suggested that habitat quality may not be important for this species and it may actually prefer scrubby forest, especially where there is a high proportion of bamboo (R. Hutchinson in litt. 2012). Also, this species is very difficult to detect (R. Hutchinson in litt. 2012) and so although it is described as uncommon, it may be more common than suggested by field observations (del Hoyo et al. 2007).
If this information is confirmed, and this species is found at more than ten locations, it would no longer qualify as Vulnerable and would warrant downlisting to Near Threatened under criterion B1ab(ii,iii,v) of the IUCN Red List, on the basis that it approaches the thresholds for Vulnerable.
The term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat. (IUCN 2001). For example, where the most serious plausible threat is habitat loss, a location is an area where a single development project can eliminate or severely reduce the population. Where the most serious plausible threat is volcanic eruption, hurricane, tsunami, frequent flood or fire, locations may be defined by the previous or predicted extent of lava flows, storm paths, inundation, fire paths, etc.
Information on this species’s distribution, population size and trends is welcome.
del Hoyo, J., Elliott, A. and Christie, D. (2007) Handbook of the Birds of the World, vol. 12: Picathartes to Tits and Chickadees. Lynx Edicions: Barcelona, Spain.