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). It is also an Important Bird Area (IBA) (Allen et al. 2019). 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). No records were found at Candaba in surveys conducted in 2017, with no further records in 2019 (Allen et al. 2019). 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).
Conservation Actions Proposed
Attempt to locate the breeding areas in north-eastern China and adjacent areas of Russia, particularly using call-playback; survey wetlands in the Philippines to try and locate further wintering sites; and initiate a new ringing programme at Dalton Pass and other migrant trapping locations. Map the Candaba Marsh area with information regarding vegetation types (Allen et al. 2019). Investigate the potential for stable isotope analysis of museum specimens to identify river catchments in which the species breeds, or previously bred.
Investigate whether marshland in the vicinity of Candaba should be included under a Ramsar designation. Provide training in surveying and identifying the species. List it as a protected species in China.
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, Allen 2020). There are also previous winter records from Taiwan, China. 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). The species continued to be absent at Candaba Marsh during surveys in 2017, with no further records in 2019 (Allen et al. 2019). 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 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).
China, Philippines, Taiwan, Province of China
The population size is very difficult to estimate given the poor quality of historic data and the paucity of recent sightings. In 2016, the population size was set at fewer than 1,000 mature individuals (250-999) based on the paucity of records. This attrition of sightings has continued, with only a single probable record (in 2019) between 2016 and 2021. The population may therefore now be very small (<50 mature individuals), although there remains substantial uncertainty in this inference given the lack of surveys on its (thus far undiscovered) breeding grounds. The population is therefore suspected to number 1-999, although it is acknowledged that this represents little more than a best guess.
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). Uncultivated areas that in the past served as refuges for many migratory species, as well as an important site for ecotourism has in recent years overgrown with floating vegetation due to high cost of clearing (Allen et al. 2019). Open water areas are now limited whilst other areas continue to be cultivated for rice. 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.