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). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to 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.
The species is reported to be still well represented at some wetland sites in both eastern and southern Africa, especially in Uganda, Botswana and Zambia (Ferguson-Lees et al. 2001). In South Africa, c.3,000-6,000 pairs remain, but populations are declining here (Barnes 2000), as is the case in some other parts of its peripheral range (Brown et al. 1982, Ginn et al. 1989). However, in some huge countries such as Zambia suitable habitat is extensive and the species is still locally common (F. Dowsett-Lemaire and R. J. Dowsett in litt. 2000). The population is preliminarily estimated to number between 10,000-100,000 individuals.
The population is declining owing to drainage and damming of wetland habitats, loss of habitat through over-grazing and human disturbance and , possibly, poisoning owing to over-use of pesticides.
This species is resident in wetlands from South Africa north to Democratic Republic of Congo and southern Sudan. The extensive Okavango marshes (Botswana) are probably its stronghold (Harrison et al. 1997a).
The species breeds in wetlands, foraging primarily over reeds and lake margins (Harrison et al. 1997a). Its diet consists largely of small mammals, particularly striped mouse Rhabdomys pumilio (Kemp and Dean 1988).
Drainage, burning and grazing of wetlands have probably led to general declines, although these have been partly mitigated by adaptation to new wetlands created by dams (Ginn et al. 1989) and sewage-works (Barnes 2000). The Okavango marshes are threatened by water abstraction (R. Simmons in litt. 1999), and there has been massive drainage of wetlands in KwaZulu-Natal (Begg 1986). Accumulation of chemical pollutants in eggs may be responsible for poor hatching success, although it does not appear to have an effect on adult reproductive output (de Kock and Simmons 1988, R. Simmons in litt. 1999).
Text account compilers
Butchart, S., Ekstrom, J., Harding, M. & Symes, A.
BirdLife International (2022) Species factsheet: Circus ranivorus. Downloaded from http://www.birdlife.org on 28/06/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 28/06/2022.