The genus Circus is a cosmopolitan genus of about ten species. They are medium-sized, slender hawks, the female being considerably larger than the male. They are characterised by long, narrow, rounded tails, small beaks and long, slender legs. The most notable characteristic is the owl-like ruff of facial feathers that cover unusually large ear openings – an adaptation not for low-light hunting, but to locate prey by their rustling and squeaking in tall grasses.
|wingspan min.:||0||cm||wingspan max.:||0||cm|
|size min.:||47||cm||size max.:||53||cm|
|incubation min.:||32||days||incubation max.:||36||days|
|fledging min.:||36||days||fledging max.:||41||days|
Video Black Harrier
copyright: Francesc Capdevila i Torrell
The species has conceivably lost 50 % of its preferred breeding habitat over the last century, and present rates in the Overberg may be over 1% per annum. Habitat is primarily lost to agriculture, and this is compounded by the uncontrolled burning of fynbos and grassland, which renders these habitats unsuitable for breeding for about five years. Alien vegetation and urbanisation are also cited as causes of habitat loss. In south-western South Africa, it is thought that breeding birds have been displaced from prime lowland habitats (renosterveld and fynbos) by the spread of cereal agriculture, with breeding pairs presently occupying only coastal areas, with high productivity, and montane habitats, where breeding success is low and levels of nest predation are high. Rodent populations in areas of wheat cultivation may be as low as 33% of those found in renosterveld vegetation, and remnant patches of renosterveld, which continue to be degraded, hold lower numbers of rodents than coastal strandveld vegetation. Low hatching rates, possibly as a result of high pesticide residues, is an increasing threat now that many remaining breeding habitats are surrounded by agricultural areas. The ingestion of herbicides and pesticides may account for the death of some adults in South Africa, while road deaths adjacent to west coast breeding grounds numbered six birds over one breeding season in 27. Drainage, impoundment and inappropriate management of vleis, marshes or streams near breeding grounds could prove detrimental. Climate change in South Africa is predicted to cause a decrease in overall winter rainfall in the core breeding areas, which is likely to lead to a reduction in mouse populations and disruption to breeding. The same threats may apply to the species in Namibia, and the favoured habitats of the migrant population may be overgrazed, particularly in southern Namibia. Overgrazing in southern Namibia is attributed mainly to resident pastoralists and ’emergency grazing’ by farmers from elsewhere, which is offered during years of good rainfall.