Justification of Red List Category
This poorly known warbler has been uplisted from Vulnerable on the basis of the declining frequency of already very scarce records, suggesting that its population is smaller than previously thought. It qualifies as Endangered because it is thought to have a very small population, which is in decline owing to habitat loss and degradation in its wintering grounds, and possibly in its breeding range. Its breeding grounds are in urgent need of discovery.
The global population is assumed to be very small, i.e. fewer than 1,000 mature individuals, based on the paucity of recent records (Round and Allen 2010, D. Allen in litt. 2016, W. Heim in litt. 2016, T. Townshend in litt. 2016, ); it is placed in the band for 250-999 mature individuals, equivalent to 375-1,499 individuals in total.
The population appears to be continuing to decline, with the frequency of records continuing to reduce. There were 18 sightings of a total of 69 birds in 1981-1990, compared with only 11 sightings of 22 birds in 1991-2007 (Round and Allen 2010). Since 2007, there have been 11 reported sightings, all of single birds, and only one of these has supporting documentation (T. Townshend in litt. 2016).
A moderate and continuing population decline is suspected, owing to the paucity and declining frequency of recent records (Round and Allen 2010) and on-going habitat destruction in its wintering grounds (D. Allen in litt. 2012).
Acrocephalus sorghophilus has occurred on passage in Liaoning, Hebei, Hubei, Jiangsu, Fujian and Beijing in eastern China, and Taiwan (China), where there are eight confirmed records (Yang Liu in litt. 2007). The species is believed to winter in the Philippines, but there have been no records since 2009 (D. Allen in litt. 2016). There are also previous winter records from Taiwan. In the Philippines it occurred at Candaba and has been trapped Dalton Pass (Luzon), although there have been no records from Dalton Pass since 1970 and the species has been very scarce at Candaba since the mid-1990s (P. Round et al. in litt. 2008), despite increasing observer effort (D. Allen in litt. 2012). There has also been an increase in observer effort at migration watch sites in eastern China, but records remain scant (D. Allen in litt. 2012). It is presumed to breed in north-eastern China (probably in Hebei, Liaoning, Jilin and Heilongjiang provinces) and adjacent areas of Russia, namely the Amur region (Kennerley and Pearson 2010). There was a relatively recent record of a singing male at Muraviovka (Russia) (P. Fabien in litt. 2004), although a subsequent search of the site failed to find any individuals (P. Leader in litt. 2007) and recent intensive fieldwork at Muraviovka is yet to record the species (W. Heim in litt. 2016). Almost all recent records concern reported individuals presumed to be on passage in northeast China. Yet this still represents very few records since the late 1990s, with only about five noted in Beijing and Hebei during migration seasons in the four-year period 2008-2011 (Yang Liu in litt. 2012). The most recent record is a single individual reported at fishponds near Liaotieshan, Dalian, Liaoning on 26th September 2015 (T. Townshend in litt. 2016). Two were reported in 2014, one in June and one in September (T. Townshend in litt. 2016).
On passage, it has been recorded in millet crops and marshland, and in winter it occurs in reed and grass marshes, often near water. It potentially uses willow scrub and reedbeds in its breeding range (Kennerley and Pearson 2010). It probably feeds largely on invertebrates, and may also consume seeds, although this requires confirmation (D. Allen in litt. 2012). Spring passage in China is from late May to early June, with autumn passage from late August to early September. All Philippine records are from September to June.
Habitat destruction on the wintering grounds is likely to be causing a decline. At Candaba, almost all marshland has been destroyed through conversion to rice cultivation and fishponds. In addition, local people there burn reeds and other native vegetation to encourage new shoots for livestock to graze on (P. Round et al. in litt. 2008). The banks of Laguna de Bay are being occupied by settlers and factories so that the reedbeds are becoming highly fragmented and greatly reduced in area and at Bukal, Laguna, most reedbed has been drained for conversion to poultry-processing factories. The conversion of wetlands for agricultural use in north-eastern China may also be contributing to a population decline (Kennerley and Pearson 2010). The impacts of the extensive use of insecticides to reduce mosquito and other invertebrate populations may have been to considerably reduce food availability at critical times for the species. Trapping birds for food and for sale as cagebirds is frequently conducted at reedbed sites and may have severely affected this species, particularly given the potentially extremely limited number of suitable sites that remain in the wintering range.
Conservation Actions Underway
CMS Appendix II. All bird species are legally protected in the Philippines. Candaba Marsh has been proposed as a Ramsar Site and education material has been prepared; however, most habitat there has now been converted (D. Allen in litt. 2012). Surveys by a team from the Wild Bird Club of the Philippines (WBCP) and the Wetland Trust were conducted at Candaba in late April 2008 and March 2009, with the aim of locating the species; however, it was not recorded and the survey documented a lack of extensive suitable habitat (Round 2008, P. Round et al. in litt. 2008). The species had been recorded a few days before the survey, representing the first confirmed record there for seven years. A mist-netting survey was carried out at Candaba and other wetland sites in March 2009 in which one individual of this species was trapped and subsequently appears to have been the first published record of moult in A. sorghophilus (Round and Allen 2010). An expedition to Dalton Pass in October 2009 did not record the species (P. Round per Sykes 2009). WCBP have been working to encourage the local government of Candaba to raise awareness amongst local communities and stop the burning of vegetation (M. C. Lu per P. Round et al. in litt. 2008).
12-13 cm. Small, lightly streaked warbler. Pale buff upperparts with faint dark streaking on mantle and scapulars and bright buff rump, tinged rufous. Faintly streaked crown with prominent black lateral crown-stripe over broad creamy-buff supercilium. Buff-ochre underparts with whiter throat and belly. Similar spp. Black-browed Reed Warbler A. bistrigiceps has uniform olive-brown upperparts, lacking streaking on crown, mantle and scapulars.
Text account compilers
Mahood, S., Benstead, P., Crosby, M., Peet, N., Gilroy, J., Martin, R, Taylor, J.
Jensen, A., Round, P., Allen, D., Johnson, R., Leader, P., Yang, L., Bajarias, M., Fabien, P.
BirdLife International (2020) Species factsheet: Acrocephalus sorghophilus. Downloaded from http://www.birdlife.org on 15/07/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 15/07/2020.