The Black Harrier is the focal bird species for our Overberg Threatened Bird Awareness Project for March 2017.
The Black Harrier, Circus maurus, is endemic to southern Africa and is the world’s most range restricted continental harrier. This is one of the rarest of southern Africa’s breeding endemics; the population is estimated around 1500 birds.
The breeding range of the Black Harrier is limited to South Africa, and is concentrated in the coastal and montane regions of the Western Cape. The rarity of the species is directly linked to the shrinking of its habitat. This transformation of their range, by agriculture and invasive alien plants, coupled with habitat fragmentation, pose the major threat to this species. This trend is likely to be exacerbated in the future by further development as well as climate change.
The utilization of breeding areas by Black Harriers reflects our current landscape. Coastal and mountainous areas do not have agriculture as the predominant land use, with agricultural development being concentrated to the relatively flat, fertile lowlands. Presently, more than 90 % of the Cape lowlands have been transformed by agriculture and while the montane regions are well protected as mountain catchments and provincial nature reserves, the breeding success of the species is lowest in this habitat. In protected coastal areas with high rodent populations, the birds manage to raise on average two young per breeding attempt, in stark contrast to mountainous terrain where more than half of all nests fail. Though the harriers do utilize the transformed landscape for foraging, they seem incapable of actively nesting in these areas.
Many harriers move away from their breeding grounds at the end of the breeding season and researchers are attempting to discover where these birds move to and why they suffer such high mortality rates during the non-breeding season. Studies have shown unusual behavior such as regular night time activity, foraging distances from the nest of up to 50 kilometers as well as an appreciable selection for cooler climates. The selection for cooler climates in both breeding and non-breeding seasons illustrates the intolerance of the species for high temperatures, another possible explanation for the selection of coastal and montane habitat types.
Studies on birds fitted with satellite tracking equipment have shown that harriers can travel in excess of 300 kilometers per day. The migration routes of the harriers will need to be determined as this will in all likelihood increase the threat posed to the species by wind farm developments. Wind farms and their location in the landscape will need to be informed by the migration patterns of harriers, amongst other bird species, to minimize impact on population numbers.
As the trend of habitat transformation continues to grow through increased agriculture and urbanization, a species such as the Black Harrier, which is reliant on natural vegetation for nesting sites, will continue to see a contraction of viable habitat that it may utilize for breeding. The conservation of natural fragments in a manner that can protect the ecological integrity of the landscape is crucial to the future success of this species. This is a battle that, at the moment, is being lost.
Black Harriers are listed as Vulnerable according to the IUCN.
Should you wish to assist the Overberg Crane Group with our conservation initiatives please contact Mick D’Alton at firstname.lastname@example.org.
Photo credit: Sharon Brink