Modeling the distribution of Nonggang Babbler Stachyris nonggangensis, a threatened bird of limestone karst forests of the Sino-Vietnam border, and implications for its conservation

Abstract

Information on the geographic distribution of a species is fundamental for its conservation. Nonggang Babbler Stachyris nonggangensis (NB) is a rare and newly discovered species that is restricted to limestone karst forest on the Sino-Vietnamese border and has been classified as 'Vulnerable' due to its narrow distribution. However, the extent of the habitat suitable for NB is poorly known. We conducted a species distribution model (SDM) using 33 occurrence data and nine environmental variables. The SDM suggested highly suitable habitat covers 541 km2, and habitat with a medium and low level of suitability covers 3,218 km2 and 722 km2, respectively. Of the entire suitable habitat (low through high), 25.8% is in northern Vietnam and the rest is in Guangxi Zhuang Autonomous Region, southern China (especially concentrated in northern Longzhou and southern Daxing Counties). Unfortunately, only 12.4% of the entire suitable habitat is known to be occupied, and the habitat outside the reserves is highly threatened by fragmentation and degradation. Globally, NB is apparently isolated in only four sites, including one site in which we discovered its presence during field validation of the model. Based on this work, we suggest upgrading NB to the 'Endangered' category on the IUCN Red List and adding it to the list of endangered species of both China and Vietnam.