LC
Western Marsh-harrier Circus aeruginosus



Justification

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 increasing, 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.

Population justification
In Europe, the breeding population is estimated to number 99,300-184,000 breeding females, which equates to 199,000-367,000 mature individuals (BirdLife International 2015). Europe forms approximately 48% of the global range, so a very preliminary estimate of the global population size is 415,000-765,000 mature individuals, although further validation of this estimate is needed. It is placed in the band 500,000 to 999,999 mature individuals.

Trend justification
In Europe, the population size is estimated to be increasing (BirdLife International 2015).

Ecology

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).

Threats

Major 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 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). The species is also highly vulnerable to the effects of potential wind energy development (Strix 2012). 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).

Acknowledgements

Text account compilers
Butchart, S., Ekstrom, J., Harding, M., Khwaja, N. & Ashpole, J


Recommended citation
BirdLife International (2021) Species factsheet: Circus aeruginosus. Downloaded from http://www.birdlife.org on 16/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 16/10/2021.