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The regional population of the near-endemic Black Harrier Circus maurus has been quantified at less than 1 000 mature individuals with an estimated continuing decline of at least 20% within the next two generations. In addition, at least 95% of mature individuals are present within a single sub-population.
The Black Harrier is one of the most range-restricted harrier species in the world, with the core of its range located in the Fynbos Biome of south-western South Africa (Simmons 2000). Peripheral populations extend to the southern reaches of the Karoo and Grassland biomes (Curtis et al. 2004). The species is thought to have lost up to 50% of its core breeding habitat in the last century owing to extensive land transformation by agriculture (particularly in the Overberg), invasive alien vegetation, and urbanisation within the Fynbos Biome (Curtis et al. 2004). An isolated population of about 10 mature individuals occurs in northern coastal Namibia, where they may breed. Within the region, the species is restricted to South Africa and Lesotho where it has a large Extent of Occurrence (400 000 km2), with the highest densities occurring in Western Cape as well as the grasslands of Free State and Eastern Cape provinces. The Black Harrier has a polarised distribution in the Fynbos Biome, with breeding birds restricted to the coastal strip and inland in the mountains (Curtis et al. 2004). This distribution is a reflection of the birds' preference for cooler south-facing slopes and mountains, as well as land-use patterns in the region, with intensive agricultural development being concentrated on the flat, relatively fertile lowlands but largely absent along the coastal strip and steeper mountain slopes (Curtis et al. 2004, Jenkins et al. 2012). Black Harriers undergo seasonal migrations during the summer (see map): travelling as far as 1 200 km eastwards to Lesotho and Free State grasslands, from the Western Cape, returning in winter (RE Simmons unpubl. data). The species can be irruptive in certain areas such as Free State grasslands and Northern Cape, in response to food availability, being abundant one year and completely absent the next (BD Colahan and RE Simmons unpubl. data).
The global population of the Black Harrier is estimated to be less than 1 000 mature individuals. Only c. 10 mature individuals occur outside of the region. The confidence in this estimate is high.
The population is thought to have undergone a major (85%) decline in the past 100 years (17% in 20 years) owing to loss of large swathes of indigenous Renosterveld vegetation in parts of the Overberg, Western Cape (Curtis 2005). Indeed, in the Western Cape the species is estimated to have declined by at least 50%, with birds having disappeared from the Cape Flats as well as the Overberg (Curtis 2005). It is predicted that the species will undergo a continuous decline of greater than 20% over the next two generations (15 years). The confidence in this population trend estimate is medium.
The main threats facing this species include habitat loss and fire (Barnes 2000). Almost no nests occur in transformed lowland landscapes (Curtis et al. 2004), and transformation over the past 150 years has resulted in 90% of the fertile, lowland areas of the western and south-western coastal plains being lost (Kemper et al. 2000), representing a significant decrease in breeding habitat for Black Harriers. Birds are thus forced to breed in sub-optimal locations (i.e. montane areas) which require adults to travel further to provision their chicks. The longer distances and time spent away from the nest affect the frequency of food provision, which depresses clutch size and nestling growth rates (Jenkins 2000). It also increases the levels of predation in these areas relative to coastal regions (Curtis et al. 2004). A large proportion of the population is found on private land and hence is susceptible to changes in land-use (Chadwick 1997). About 60% of the 150 breeding sites known are found in protected areas, suggesting that intact habitats and prey bases are essential for the wellbeing of this species. The population of the species appears to fluctuate, possibly with fluctuations in its prey-base, which is mainly small rodents (Barnes 2000, Simmons et al. 2005). Long-term impacts that depress the abundance of small mammals are likely to consequently affect Black Harrier numbers. Other long-term threats include climate change impacts such as decreasing rainfall and increasing temperature in their core breeding areas on the West Coast (B Hewitson pers comm.). A decrease in ground moisture is likely to reduce suitable nest sites (because damp areas are preferred) and decrease mouse populations that breed less prolifically in dry conditions (Retief 2011). More frequent fires, which are being experienced in Western Cape, are also likely to cause declines in both breeding and food requirements. The proliferation of wind farms in the core breeding areas (Western Cape coast to Northern Cape), as well as in the newly discovered summer range in Lesotho, means that harriers may be impacted at both ends of their migratory cycle. This is an unknown threat, but the species is high on the collision-sensitivity list of the Birds and Wind Energy Specialist Group.
Black Harrier breeding ecology and threats have been studied in a 12-year programme run under the auspices of the Percy FitzPatrick Institute of African Ornithology, University of Cape Town. The focus has been on the effects of habitat fragmentation and the utility of Black Harrier as indicators of biodiversity health in global biodiversity hotspots in Western Cape. A large group of harrier enthusiasts assists in monitoring birds from KwaZulu-Natal to Northern Cape, and Black Harriers are now part of the BirdLife South Africa Species Champions Programme. In the early 2000s, work was undertaken towards establishment of a stewardship programme in the Overberg in which farmers were encouraged to practice conservation-friendly farming to benefit the few remaining pairs of harriers there. A pilot study was recently undertaken to examine the dispersal and behaviour of satellite-tagged Black Harriers with a focus on discovering where they disperse to in the winter as well as movement, home range and survival away from core breeding areas and how this influences population numbers.
A Species Action Plan, as well as Biodiversity Management Plan, is recommended. The importance of conservation actions in Lesotho has only recently come to light; conservation measures must include the cooperation of the Lesotho government. Migration periods appear to be the time of highest mortality for Black Harriers, and ways of reducing mortality during migration should be investigated.
* Comprehensive data on harrier foraging and breeding performance in different habitats, and under different conditions in the non-breeding period, are required.
* Demonstration of a link between the welfare of harrier pairs and the ecological integrity of habitat fragments in the Fynbos Biome, could establish this species as an indicator species for broader conservation initiatives in this biome.