Justification of Red List Category
This species qualifies as Vulnerable because it is likely to have a small, declining population as a result of wetland destruction in its wintering grounds, compounded by limited habitat loss on some islands where it breeds.
The global population size is 'unlikely to be much more than a few thousand individuals' (BirdLife International 2001), while national population estimates include: < c.100 breeding pairs and < c.1,000 individuals on migration in China; < c.50 individuals on migration and < c.50 wintering individuals in Taiwan; c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Korea; c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Japan and c.100-10,000 breeding pairs and c.50-1,000 individuals on migration in Russia (Brazil 2009). The total population is placed in the band 2,500-9,999 mature individuals, equating to 3,750-14,999 individuals, rounded here to 3,500-15,000 individuals.
Various human activities are negatively affecting both breeding and wintering habitats for this species, suggesting that moderate population declines are likely to be continuing.
Locustella pleskei is a localised breeder on small islands in Peter the Great Bay in the extreme south of far eastern Russia, the Izu Islands and islands off Kyushu, Japan, and islands off South Korea and probably North Korea. It has also recently been recorded breeding on islands of the coast of eastern China (Qiao et al. 2006), where it also occurs as a passage migrant, and presumably winters in coastal wetlands in south China, although the only confirmed records are from Hong Kong (China). Recent winter sightings in north-eastern Vietnam suggest that this may also be a significant wintering area (J. Pilgrim in litt. 2008). The population is unlikely to be more than a few thousand individuals, although it is poorly known, as many offshore islands remain unsurveyed and it is relatively difficult to detect.
It breeds in open, wet areas of thick grasses and reeds and in areas of low bushes. In its wintering range, birds have been found in extensive reedbeds, low shrubs near reedbeds and mangroves. It probably holds territories in winter. On the Izu Islands, it breeds from May-June with clutch-sizes ranging from 3 to 6 eggs. It is skulking and reluctant to fly.
The main threats are likely to be habitat loss and degradation, although the extent to which these are affecting it is currently unclear. Degradation of wintering habitat may not be of high concern, as the species is known to occur in a fragment of degraded mangrove forest in Vietnam; however, better quality habitat has not been adequately sampled for comparison (S. Mahood in litt. 2012). In Russia, and possibly North Korea, the large-scale Tumangan Project could lead to increased human disturbance and pollution, possibly affecting islands where it breeds. A camping ground or marine park is planned for Toga Point on Miyake-jima (Izu Islands), which would destroy an important area of habitat. A volcanic eruption on Myiake-jima in 2000 led to a halving of the population on that island (Fujita et al. 2005). There is continued extensive loss of wetlands in its wintering range and the reedbeds in Deep Bay, Hong Kong, may be one of the largest areas of such habitat left in south China. Illegal trapping using mist-nets is common in some coastal areas in China during migration seasons and probably results in some mortality in this species (Liu Yang in litt. 2012).
Conservation Actions Underway
CMS Appendix II. One of its wintering sites is protected at the Mai Po Marshes Nature Reserve, which is also included inside the Mai Po Marshes Ramsar Site. A long-term ringing programme at this site has contributed to knowledge of its winter habitat requirements and abundance.
13-14 cm. Dull, unstreaked warbler. Uniform olive-grey upperparts with faint, dark mottling on mantle. Indistinct pale cream or grey supercilium with whitish eye-ring. Whitish underparts suffused with pale buff on flanks and sides of breast, although much darker on some birds. Similar spp. Middendorf's Grasshopper Warbler L. ochotensis has browner mantle and scapulars, more noticeable supercilium and eye-stripe and pale outer web to the long, outermost primary. Generally paler underparts.
Text account compilers
Benstead, P., Gilroy, J., Khwaja, N., Taylor, J.
Pilgrim, J., Liu, Y., Mahood, S.
BirdLife International (2022) Species factsheet: Helopsaltes pleskei. Downloaded from http://www.birdlife.org on 03/07/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 03/07/2022.