Data Zone
Justification of Red List category
This species qualifies as Vulnerable because it has a small, declining population as a result of habitat loss in both its breeding and wintering grounds.
Population justification
The global population estimate of 2,500-9,999 mature individuals is based on a detailed analysis of records by BirdLife International (2001), where it was concluded that the species must have a fairly small world population (i.e. fewer than 10,000). This estimate equates to 3,750-14,999 individuals, rounded here to 3,500-15,000 individuals. All individuals are considered to belong to a single population on the basis of the migratory nature of the species and the lack of clear division within the known breeding range of the species.
Trend justification
Although perhaps more common than it was thought to be in the 1990s, this species is suspected to be continuing to decline at a moderate rate, owing to the conversion of many natural systems. While it may be tolerant of some modified habitats, the species is unlikely to cope with heavily intensified agricultural and urban environments.
Acrocephalus tangorum breeds in south-east Russia and north-east China, and winters in southern Laos, Cambodia, Thailand and Peninsular Malaysia (BirdLife International 2001, Kee and Bakewell 2015). It occurs as a scarce passage migrant in Hebei, Liaoning and Hong Kong in China, Pakxan wetlands in Lao (W. Duckworth in litt. 2012) and in Vietnam. Few breeding sites are known. In China, Alström et al. (1991) reported that the species was locally common at Zhalong National Nature Reserve and is still present at Dalai Hu National Nature Reserve, Inner Mongolia, but little habitat remained at two other known sites. In Russia Khanka Lake is the best known site, though updated data on the size and trend of the population is required.
Grasslands within the Tonle Sap floodplain in Cambodia are perhaps the most important wintering habitat and it has been noted to be locally common (Bird et al. 2007, Bird et al. 2012), however declines have been noted within the last decade (Goes 2013). Elsewhere the species is decidedly localised and rare, with small numbers regular at Khao Sam Roi Yot, Thailand, and recent observations in Perlis and Pulau Pinang in Malaysia (Kee and Bakewell 2015). The paucity of recent records for well-watched and increasingly heavily monitored and ringed sites (such as Mai Po in Hong Kong and Bung Boraphet in Thailand) suggest it is genuinely very scarce (P. Round in litt. 2012).
In China, it occurs in reedbeds and, in Hong Kong, has been recorded from reeds around overgrown fields and fishponds. At Khao Sam Roi Yot, it is largely confined to Phragmites-dominated reedbeds where it has been recorded at higher densities than any other site (Round and Rumsey 2003, Bird et al. 2007, Bird et al. 2012). Recent observations in Cambodia have come from a variety of habitats, particularly tall grass stands (away from water) and sedge beds (both wet and dry), scrub-fringed lotus swamps, and heterogeneous scrub/grass mixes away from water (P. Davidson in litt. 2003). Importantly, the species occurs at similar densities in suitable human modified habitats as it does in natural tall grasslands on the Tonle Sap floodplain (Bird et al. 2007). However, it may be that large expanses of optimal habitat are required to sustain its presence within smaller (possibly suboptimal) habitat patches (P. Round in litt. 2012).
The main threat on its breeding and wintering grounds is habitat loss, including the loss and degradation of Phragmites marsh in Thailand, such that there is now very little suitable habitat remaining in the entire country. At Khao Sam Roi Yot, freshwater marsh has suffered greatly from encroachment with plantations of casuarinas, eucalyptus and coconut palms, and the establishment of prawn farms with salt and brackish water. This situation is likely to continue. Elsewhere in the country, marshes are threatened by reclamation and urbanisation and no freshwater swamp habitat lies within any protected area. Habitat loss and degradation is continuing at Pakxan wetland, an important stopover site in Lao, where the tall emergent grasses favoured by the species are routinely removed by local people and changes to water management for irrigation and flood control have caused the loss of some waterbodies (W. Duckworth in litt. 2012, 2016). In Cambodia, the situation may be more promising as the species has been recorded in man-made headponds used for dry season rice cultivation, although its preference for tall dry grass habitat may render it susceptible to dry season burning which is extensive (Bird et al. 2007). There have also been changes to the local water control regime in Cambodia with an increase in the number of small dams and a concentration of water bodies, potentially reducing the extent of suitable habitat available during the dry season.
Conservation Actions Underway
CMS Appendix II. Attempts have been made by both international and national conservation organisations to secure the future of Khao Sam Roi Yot. To date these have been unsuccessful. The species was the focus of specific study on the Tonle Sap floodplain, the results of which revealed that it may not be immediately threatened in the area. It may benefit from Integrated Farming and Biodiversity Areas designed to retain semi-natural systems on the Tonle Sap floodplain.
13 cm. Small, drab reed-warbler. Uniform tawny-rufous upperparts. Bold, whitish supercilium bordered by dark brow and narrow eye-stripe. White chin, throat and belly becoming buffish-brown on flanks. Similar spp. Paddyfield Warbler A. agricola has less tawny-rufous upperparts and less clearly defined black eyebrow. Black-browed Reed-warbler A. bistrigiceps has more extensive dark crown and more obvious contrast between the black brow and pale centre of crown. Generally duller and more olive-brown upperparts. Voice Typical Acrocephalus song. Calls include a sharp chik-chik, a harsh chr-chuck and a slurred zack-zack.
Text account compilers
Peet, N., Martin, R, Benstead, P., Westrip, J., North, A., Bird, J., Taylor, J., Allinson, T
Contributors
Mulligan, B., Hornskov, J., Davidson, P., Duckworth, W., Round, P.
Recommended citation
BirdLife International (2024) Species factsheet: White-browed Reed-warbler Acrocephalus tangorum. Downloaded from
https://datazone.birdlife.org/species/factsheet/white-browed-reed-warbler-acrocephalus-tangorum on 23/12/2024.
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 23/12/2024.