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 10 years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in 10 years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
In Europe, the breeding population is estimated to number 151,000-243,000 breeding females, which equates to 303,000-485,000 mature individuals (BirdLife International in prep.). Europe forms approximately 48% of the global range, so a very preliminary estimate of the global population size is 631,000-1,010,000 mature individuals, although further validation of this estimate is needed. It is placed in the band 600,000 to 1,100,000 mature individuals.
In Europe, the population is estimated to be stable (BirdLife International in prep.). Thiollay (2006) did not find a significant change in numbers of the species overwintering in West Africa during 1969-2004. However, recent surveys of wintering birds in Pakistan and India have shown a decline in this species at certain sites (Bibi et al. 2016; Ganesh & Prashanth 2018), although it is unclear whether this represents a range shift or a true population decline. In the absence of data from the rest of its breeding range, and with no known significant threats, the global population is currently suspected to be stable.
Behaviour It is mainly migratory, with populations in Western Europe, North Africa and at the south of its range in Asia being generally resident (del Hoyo et al. 1994, Ferguson-Lees and Christie 2001). Migrant birds leave their breeding grounds in September and October, wintering from France south as far as sub-Saharan Africa, and east as far as the Middle East (del Hoyo et al. 1994). They begin their return journey in February and March, arriving in March and April (del Hoyo et al. 1994, Snow and Perrins 1998, Ferguson-Lees and Christie 2001). Migration is generally on a broad front, although there is some concentration at a few sites (Brown et al. 1982). Hundreds of birds occasionally gather at roosting sites, sometimes with other harriers such as C. pygargus, but otherwise they are usually solitary, associating only temporarily at especially rich feeding sites (del Hoyo et al. 1994, Snow and Perrins 1998, Ferguson-Lees and Christie 2001). They have a slightly greater tendency to be gregarious while on migration but the above still generally applies. Birds fly c. 10-30 m above the ground (Brown et al. 1982). Habitat The species inhabits extensive areas of dense marsh vegetation, in fresh or brackish water, generally in lowlands but up to 2,000 m in Asia and 3,000 m on its wintering grounds in Cameroon (del Hoyo et al. 1994). Diet It is a generalist predator taking a variety of prey types, with small birds generally preferred but mammals such as voles, rabbits and rats being more important in parts of its range (del Hoyo et al. 1994). Breeding site The nest is a pile of reeds built in dense marsh vegetation (del Hoyo et al. 1994). Management information The species requires extensive wetland in its breeding range (del Hoyo et al. 1994).
Main threats include wetland desiccation and drainage; persecution by shooting; pollution, especially from excessive pesticide use in and around wetlands (although widespread bans have reduced this threat somewhat), and poisoning by heavy metals, notably the consumption of lead-shot through feeding on contaminated waterbirds (del Hoyo et al. 1994, Ferguson-Lees and Christie 2001, Orta et al. 2014). The species increasingly breeds and hunts in farmland, therefore loss of prey through agricultural intensification may pose an increasingly significant threat (Keller et al. 2020). Molins-Delgado et al. (2017) found evidence for high levels of UV filters (used in sunscreens) in unhatched eggs of Western Marsh-harrier in Spain, which may have endocrine-disrupting effects. The historical threat of hunting in southern Europe has mostly subsided, but illegal shooting is still rife locally, notably on Malta (Ferguson-Lees and Christie 2001). High levels of persecution have also been reported in Iraq (Al-Sheikhly & Al-Azawi 2019). Buij et al. (2016) found the species for sale at fetish and bushmeat markets in Benin, Burkina Faso, Mali, Nigeria and Togo. Live birds are traded at bird markets in Kuwait (Al-Sirhan & Al-Bathali 2010) and Iraq (Al-Sheikhly & Al-Azawi 2019). The species is highly vulnerable to the effects of potential wind energy development (Strix 2012), and suffers mortality due to electrocution by power lines in some European countries (pressures and threats data reported by EU Member States under Article 12 of the Birds Directive for the period 2013-2018). In its West African range, the species is vulnerable to habitat degradation through wood harvesting and overgrazing as well as exposure to pesticides (Thiollay 2007). Grassland habitats in India, an important overwintering habitat for this species, are being lost due to urbanisation and industrialisation (Ganesh & Prashanth 2018). Changes in precipitation due to climate change may pose a future threat (pressures and threats data reported by EU Member States under Article 12 of the Birds Directive for the period 2013-2018).
Conservation actions underway
The species is listed on CITES Appendix II, CMS Appendix II and Raptors MoU Category 3. It is monitored by systematic breeding surveys in at least 12 European countries (Derlink et al. 2018). It is also 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).
Conservation actions needed
Further research is needed to evaluate population trends in Central Asian breeding areas, as surveys of overwintering birds in India and Pakistan suggest a possible decline (Bibi et al. 2016; Ganesh & Prashanth 2018).
Text account compilers
Ashpole, J, Butchart, S., Ekstrom, J., Harding, M. & Khwaja, N.
BirdLife International (2023) Species factsheet: Circus aeruginosus. Downloaded from http://datazone.birdlife.org/species/factsheet/western-marsh-harrier-circus-aeruginosus on 28/05/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 28/05/2023.