Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (extent of occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size has not been quantified, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Ferguson-Lees and Christie (2001) estimate the population at 20,000-30,000 pairs which equates to 40,000 to 60,000 mature individuals. The species is described as generally rare in Russia and uncommon in northern Japan (del Hoyo et al. 1992).
The population is suspected to be stable in the absence of evidence for any declines or substantial threats. Monitoring surveys of wintering birds at roosting sites in central Japan during 1994-2009 found that numbers fluctuated from year to year, but that the overall trend was fairly stable (Hirano et al. 2010).
The species is likely to be affected by degradation and loss of wetland habitat across its range (Orta et al. 2014). In Southeast Asia where the species overwinters, wetlands are under threat from conversion to agriculture, extraction of resources (e.g. peat), pollution and clearance of mangroves (Hughes 2017). Similarly, wetlands in the species' breeding range in Russia and China are threatened by drainage, conversion to agriculture, urbanisation, mining, oil and gas exploration and pollution from agricultural discharge (An et al. 2013). In Japan, lead shot in prey items has been identified as a potential threat (Hirano et al. 2004); this threat could be more widespread across the species's range.
Conservation actions underway
The species is listed on CITES Appendix II, CMS Appendix II and Raptors MoU Category 3. It is monitored in at least parts of its range by the International Waterbird Census (>10 records received in >50% of the years that the census has been running in the relevant region).
Text account compilers
Ashpole, J, Taylor, J., Ekstrom, J., Symes, A. & Butchart, S.
BirdLife International (2023) Species factsheet: Circus spilonotus. Downloaded from http://datazone.birdlife.org/species/factsheet/eastern-marsh-harrier-circus-spilonotus on 30/05/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 30/05/2023.