Data Zone
Justification of Red List category
This range-restricted species was described as new to science as recently as 2008. It occupies a small area of limestone karst in southernmost China (Guangxi) and an even smaller area of adjacent Viet Nam. Its population size is only 2,500-5,000 mature individuals, and it is in decline because of habitat loss, modification and degradation. Accordingly, it is assessed as Vulnerable.
Population justification
The area from which this species has been proven to occur has grown considerably since its discovery (sensu Zhou and Jiang 2008). In the most detailed evaluation to date, Jiang et al. (2020) identified a realised/occupied area of habitat covering 555 km2, but with a much larger area (c. 4,500 km2) of total potentially suitable habitat, much of which remains to be surveyed; the authors acknowledged however that their course modelling approach may, in places, have exaggerated the area of suitable habitat, suggesting this should be treated as a maximum value. Nonetheless, initial field validations of their model in China suggest promising accuracy, and there is little doubt that this species occupies a (potentially much) greater area than previously supposed.
In China it is known from six places (Li et al. 2013, Yu et al. 2014, Jiang et al. 2020, eBird 2023): two areas of Nonggang National Nature Reserve (present only in Longhu and Nonggang sections; apparently absent from Longshan south of the Zuo River: Jiang et al. 2020); Chunxiu Nature Reserve; Qinglongshan Nature Reserve; Xialei Nature Reserve; and Bangliang Gibbon National Nature Reserve. Applying densities they obtained during surveys, Li et al. (2013) suggested the number of individuals may be >2,000 in Nonggang, Bangliang, Chunxiu and Trung Khanh (Vietnam [which was not surveyed as part of this study; see below]), although they do also suggest the global population may be as low as 1,500 individuals. Given the species has now been found at Qinglongshan Nature Reserve (Yu et al. 2014) and Xialei Nature Reserve (Jiang et al. 2020), these numbers now seem overly precautionary; in particular, the modelling exercise by Jiang et al. (2020) found that Xialei hosts more highly suitable habitat than anywhere else outside of Nonggang, and validated this with ground-truthing surveys, detecting 21 birds across four transects (of five) that were placed in habitat designated as highly suitable. It is therefore likely that Xialei hosts a population of several hundred birds.
In Vietnam, it is known only from the extreme north-east, in Cao Vit Gibbon Conservation Area (Eames and Truong 2016, eBird 2023), but modelling by Jiang et al. (2020) suggests a much larger area of potentially suitable habitat lies in the country. However, there are two reasons to caution against a confident assumption that Vietnam hosts a large population: (1) There remain no records in the country away from Cao Vit Gibbon Conservation Area, despite some survey effort in the areas they identify (eBird 2023), albeit not specifically for this species such that it may have been overlooked; and (2) The vast majority of karst in Vietnam is considered by Jiang et al. (2020) to be of medium/intermediate suitability (only 14.4% of highly suitable habitat is in Vietnam). In their own ground-truthing in China, areas of this suitability description predictably had comparatively low success in finding babblers; for example, three transects in 'medium suitable' habitat in Gulongshan Nature Reserve failed to find it at all. Even this, however, is not conclusive as the species evidently does not have very high detectability when not vocalising: e.g. Li et al. (2013) did not find the species at Qinglongshan, when Yu et al. (2014) did. Accordingly, much of the area in Vietnam is mapped in this assessment as 'possibly extant' rather than definitely so. Future surveys in Vietnam would be advised to target the area of karst immediately adjacent to Chunxiu Nature Reserve (China), which Jiang et al. (2020) identify as high suitability, and is an area large enough to potentially support multiple hundreds of birds.
Compiling the available data, the population is estimated to number at least 2,500 mature individuals (based on densities detected by Li et al. [2013] being applied to the area of known occupancy sensu Jiang et al. [2020]). This should however be seen as the minimum likely population, with some areas of apparently highly suitable habitat not yet surveyed for this species (Jiang et al. 2020). Nonetheless, the number is limited to a somewhat small area of available karst in this species' likely range; accordingly the maximum likely population size is estimated to be 5,000 mature individuals.
Trend justification
The population trend of this species has not been directly quantified. However, it is inferred to be declining due to ongoing forest disturbance and modification that is rendering habitat unsuitable. This species is a forest-specialist, confined to a small area of limestone karst in southernmost China and neighbouring Viet Nam where most available habitat is already mostly degraded. Its exact habitat requirements are inexactly known but the species is evidently dependent on the most intact forests, and is absent from the most degraded forests (apparently anything <40% forest cover), scrub and agricultural areas (Jiang et al. 2020, eBird 2023). In the past three generations (11 years: 2012–2023), forest cover in its range decreased by 3–4% (Global Forest Watch 2023, based on data from Hansen et al. [2013] and methods disclosed therein), mostly in the periphery of suitable habitat. This is thought to have caused slow declines over the past ten years and with only 30% of the species' suitable habitat circumscribed in a protected area, declines are likely to continue.
Stachyris nonggangensis was described in 2008 from the Nonggang Natural Reserve, China (Zhou and Jiang 2008, Jiang 2009). It is still only known from six areas (Li et al. 2013, Yu et al. 2014, Jiang et al. 2020, eBird 2023): two areas of Nonggang National Nature Reserve (present only in Longhu and Nonggang sections; apparently absent from Longshan south of the Zuo River: Jiang et al. 2020); Chunxiu Nature Reserve; Qinglongshan Nature Reserve; Xialei Nature Reserve; and Bangliang Gibbon National Nature Reserve. It is now confirmed to occur in Viet Nam, in Cao Vit Gibbon Conservation Area (Eames and Truong 2016, eBird 2023) but modelling by Jiang et al. (2020) found it likely to be more widespread in this [northeasternmost] region of Viet Nam. In particular, they identified an area of apparently highly suitable habitat in Viet Nam immediately adjacent to Chunxiu Nature Reserve.
Searches in Yunnan, China, failed to find it (Li et al. 2013) and it is unlikely the species would be found in any other range state, with karst habitat further south being occupied by S. herberti (with which S. nonggangensis forms a superspecies).
This species occupies limestone karst seasonal rainforest. Extensive observational and netting surveys in forest in the non-limestone mountains of the Sino-Vietnamese border areas of south Guangxi since 2004 failed to record the species, indicating that it has very specific habitat requirements, a fact recently backed by habitat modelling (Jiang et al. 2020). It nests in cavities in a limestone cliff or on a massif rock located on the mountainside, with nests made up of aerial roots, leaves, twigs, and soft grasses (Jiang et al. 2013). Individuals have been seen foraging in gaps between two rocks by turning over fallen leaves, apparently preying on insects and other arthropods. Single-species flocks have been observed in winter (Zhou and Jiang 2008).
The only threat to this species is the destruction, modification and degradation of habitat caused by expanding agriculture and localised extraction of timber. This is occurring currently on only a small scale, thus is suspected of causing only slow rates of decline. The correlated impacts of road building and the fragmentation of habitat is unknown. Because this species has only a very small known area of occupied habitat (<600 km2: Jiang et al. 2020) any acceleration of threats (and especially fires) could cause rapid declines in the future.
Conservation Actions Underway
In China, the species is present in Nonggang National Nature Reserve, Bangliang Nature Reserve, Chunxiu Nature Reserve, Qinglongshan Nature Reserve (Zhou and Jiang 2008, Li et al. 2013, Yu et al. 2014, Jiang et al. 2020), and Xialei Nature Reserve (Zhou Fang in litt. 2016). In Viet Nam, it is protected in the Cao Vit Gibbon Conservation Area (Eames and Truong 2016). It is not currently protected by national law in either China or Viet Nam.
16-17 cm. Dark brown babbler with heavy, dark bill, checkered white throat and whitish crescent shapes behind ear coverts.
Text account compilers
Berryman, A.
Contributors
Jiang, A., Symes, A., Westrip, J.R.S., Yu, L. & Zhou, F.
Recommended citation
BirdLife International (2024) Species factsheet: Nonggang Babbler Stachyris nonggangensis. Downloaded from
https://datazone.birdlife.org/species/factsheet/nonggang-babbler-stachyris-nonggangensis on 22/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/12/2024.