Although the historical range of this species may once have been much more extensive, it seems to be currently restricted to limestone areas in the western part of Quang Binh and Quang Tri Provinces (from 19Â°39âN, 105Â°29âE south to 16Â°10âN, 107Â°40âE), and in the eastern part of Khammouan Savannakhet Provinces in Lao PDR (Nadler et al. 2003). Its range in Lao PDR appears to be limited (Nadler et al. 2003), where it has only been recorded with certainty from Hin Nam No National Biodiversity Conservation Area (Duckworth et al. 1999). The western limit of the range of the species in Lao PDR is unclear. In Viet Nam, it is confirmed from Tuyen Hoa, Minh Hoa, Bo Trach, Le Thuy, and Quang Ninh districts in Quang Binh Province (Nadler et al. 2003) and Huoug Hoa in Quang Tri Province (BirdLife International 2005). There is no current evidence for the distribution of the species north of Quang Binh, but the extent of limestone suggests that historically it may well have occurred further north. Records from Gia Lai Province are based on misidentification. The form ebenus is restricted to Khammouane and Savannakhet Provinces in Lao PDR, with a marginal extension into the western part of Quang Binh Province, Viet Nam. The precise limits of the range are unclear, particularly in Viet Nam. The overlap zones of this form with laotum and hatinhensis are not well defined.