Located at the southern tip of the African continent, this large agricultural district stretches from Caledon to Riversdale and encompasses the area south of the N2 highway, which links these two towns. The R316 from Caledon to Bredasdorp forms the district's south-western boundary, with the area known as Overberg Rûens to its east. De Hoop Nature Reserve, which abuts this area, is a separate IBA (SA119) and supports a different suite of trigger species, while the Agulhas Plain–Heuningnes Estuary IBA (SA121) lies to the south. The topography consists of low-lying rolling hills. The maritime-influenced climate is relatively equitable; mean rainfall averages 445 mm per annum, although some areas in the eastern Rûens receive an average of only 300 mm per annum.
The landscape consists primarily of cereal croplands and artificial pastures (lucerne), with more than 95% of the natural vegetation having been transformed to agriculture. The remnants of natural vegetation are mainly Renosterveld, although they include patches of Lowland Fynbos. This vegetation and the different Renosterveld types are considered Critically Endangered due to the high degree of transformation to agriculture. Historically, this entire IBA would have comprised Renosterveld vegetation; now most of this has been lost. The 'man-made' habitats include wheat-fields and other agricultural landscapes, which do provide habitat for certain IBA trigger species, notably the threatened Blue Crane Anthropoides paradiseus.
A total of 304 bird species has been recorded for this IBA. It hosts approximately 30% of South Africa's Blue Crane population, the largest population in the world, and is thus extremely important for the species' long-term persistence. Large numbers of Blue Cranes are evident in winter when many pairs, having completed breeding activities, join large, loose flocks that congregate in this area. The IBA also provides important foraging habitat for the threatened Cape Vulture Gyps coprotheres, which breeds at a colony at Potberg in the neighbouring De Hoop Nature Reserve IBA. The Overberg Wheatbelt IBA also hosts large numbers of Denham's Bustard Neotis denhami and White Stork Ciconia ciconia in summer. Black Storks C. nigra, which breed in the surrounding mountains, are found in the area's streams and may occasionally be seen soaring overhead.
Black Harrier Circus maurus frequently occurs in the modified agricultural matrix of the Overberg region, although it requires untransformed Renosterveld habitat for breeding. The area also covers a large proportion of the global range of the Agulhas Long-billed Lark Certhilauda brevirostris, which is almost confined to stony wheat-fields and pastureland. Despite its limited range, the species appears to be secure, provided that current land-use patterns persist. Some typical Karoo birds are also found within the wheat matrix and the occasional renosterveld patches. They include Karoo Korhaan Eupodotis vigorsii and Pale Chanting Goshawk Melierax canorus.
The isolated patches of fynobs on the hill slopes above Bredasdorp and Napier, parts of which form the Heuningberg Local Nature Reserve, hold a number of Cape Fynbos EBA restricted-range species, such as Orange-breasted Sunbird Anthobaphes violacea, Cape Sugarbird Promerops cafer, Cape Spurfowl Pternistis capensis, Cape Bulbul Pycnonotus capensis and Cape Siskin Crithagra totta.
Globally threatened species are Cape Vulture, Blue Crane (approximately 6 000 individuals; CAR data 2012), Martial Eagle Polemaetus bellicosus, Black Harrier, Denham's Bustard, Secretarybird Sagittarius serpentarius and Southern Black Korhaan Afrotis afra. Regionally threatened species are Black Stork, Lanner Falcon Falco biarmicus, African Grass Owl Tyto capensis, Karoo Korhaan and Agulhas Long-billed Lark. Restricted-range and biome-restricted species common in this IBA include Cape Spurfowl, Cape Bulbul, Cape Sugarbird, Agulhas Long-billed Lark, Orange-breasted Sunbird and Cape Siskin, while Karoo Korhaan is an uncommon species in this category. Blue Crane meets the 1% or more population threshold criterion.
The area is extremely rich in highly threatened endemic flora, including the spectacular Leucadendron elimense, L. modestum and L. laxum in the fynbos regions of the IBA. The discovery of a new Proteaceae species, Serruria nova, in 1998 suggests that complete surveys of the area will yield many new endemic plants. The spectacular arum lily frog Hyperolius horstockii occurs and the Cape ghost frog Heleophryne purcelli may be found in montane rivers in the wheatbelt matrix.
The Renosterveld in this IBA comprises four different vegetation types: Western, Central and Eastern Rûens Shale Renosterveld (these three are divided roughly in equal thirds across the Rûens) and Rûens Silcrete Renosterveld, which is found only along the Breede River and nearby tributaries. All four are listed as Critically Endangered and each contains a unique suite of endemic and threatened plant species. The Eastern Rûens Shale Renosterveld also contains quartz outcrops with a distinct vegetation community that has a large number of endemic and rare plants. Six new species have recently been described from these unique micro-habitats (Curtis et al. 2013).
Mammal species likely to be very scarce in the Renosterveld were recorded on camera traps by the Overberg Lowlands Conservation Trust in 2014. These include aardwolf Proteles cristata, aardvark Orycteropus afer and honey badger Mellivora capensis. Prior to this finding, it was suspected that aardvark no longer inhabited the lowlands of the Overberg. These discoveries, combined with a suite of other mammals recorded in the Renosterveld remnants, emphasise the importance of these fragments as refugia for biodiversity.
Other mammals inhabiting the Overberg include Cape fox Vulpes chama, Cape clawless otter Aonyx capensis, striped polecat Ictonyx striatus, small grey mongoose Galerella pulverulenta, water mongoose Atilax paludinosus, yellow mongoose Cynictis penicillata, large-spotted genet Genetta tigrina, small-spotted genet G. genetta, African wild cat Felis silvestris lybica, caracal Caracal caracal, steenbok Raphicerus campestris, grysbok R. melanotis, common duiker Sylvicapra grimmia and grey rhebok Pelea capreolus.
The Overberg region once supported significant areas of a large variety of natural habitats, but has been extensively transformed by the establishment of a wheatbelt, which now occupies more than 85% of the IBA. The patches of natural Renosterveld habitat that remain are very small and isolated, and they are brimming with critically threatened populations of a range of endemic plant species that were once more common throughout this landscape. These plants are extremely vulnerable to extinction as a result of habitat destruction and physical disturbance resulting from mismanagement, such as overgrazing or frequent burning. The small remnant populations are constantly being encroached upon or mismanaged because their significance is not fully appreciated.
Agricultural activities represent the major land use in this IBA and indirectly contribute most of the threats to the area. Although much of the original Renosterveld and Lowland Fynbos habitat has already been transformed for agriculture, the farming landscape does still provide suitable habitat for certain IBA trigger species, notably Blue Crane, which seems to have benefited from the agricultural changes that have occurred over the past 30 years. Nevertheless, the remaining patches of indigenous lowland habitat in the IBA are unique and intensely threatened by further degradation. It is imperative that the remaining Lowland Fynbos and Renosterveld be conserved at all costs. Under no circumstances should this IBA description be used as motivation to increase the area under wheat or transform indigenous vegetation further.
Having originally been absent from this area, Blue Crane has recently expanded its range into the agricultural sectors of the Fynbos biome and has even become common. Flocks of Blue Cranes are attracted to cultivated fields where they may feed on fallen grain and recently germinated crops. They also gather to feed on supplementary food put out for small stock, especially in times of drought. This has earned them the enmity of some farmers, a few of whom have occasionally spread poisoned grain on their fields and around feedlots to kill cranes. Most of South Africa's cranes and their habitats, particularly in the Overberg, are on privately owned farmland; their future lies firmly in the hands of private landowners. Poisoning in the Overberg is now very rare, thanks to an effective awareness campaign by the Overberg Crane Group and CapeNature, and an extremely responsive farming community. This project should act as a model for farmer awareness schemes in other parts of South Africa. It must be emphasised, however, that many cranes can die in a single irresponsible poisoning event, and rigorous campaigning and interaction with the farming community should be ongoing so that farming practices can be monitored and mitigating measures (which reduce mortality in cranes or other species) can be employed as soon as potential problems arise.
Blue Cranes are also vulnerable to inadvertent mortality when poisons are put out to kill vermin. Crops should be sprayed with pesticides judiciously, as this practice has a detrimental effect on most animals in the food web. Foraging cranes are particularly attracted to croplands between March and July, when the crop has just been sown or is short and young. It is during this period that the birds are most likely to be poisoned. Blue Cranes, Grey-winged Francolin Scleroptila africana, Cape Spurfowl and Helmeted Guineafowl Numida meleagris can succumb to poison-soaked grain set for gerbils. Gerbils should be controlled responsibly with an environmentally friendly poison such as phostoxin or zinc phosphide and by inserting it into each gerbil burrow through a length of hosepipe rather than strewing it carelessly on the ground. Once gerbil numbers have been significantly reduced, a strategically placed pole should be erected from which owls can forage. Owls would maintain gerbil populations at reasonably low levels.
At feedlots, farmers should experiment with modifications that bar cranes from accessing the grain. For example, a wide but low horizontal roof, of shade cloth or similar material, could be erected over the feeder. This would discourage cranes from feeding there as they require clear visibility in all directions to spot potential predators. Similarly, low vertical walls could be erected around the feeder, with entrances suitable for small stock to enter and leave. Cranes avoid entering any closed or partially enclosed area.
Additional threats to Blue Cranes include overhead power cables and electricity structures, which they occasionally strike. Eskom and EWT are attempting to implement a strategy to reduce bird strikes on electricity structures, such as marking them with various devices to make them more visible to birds at sites where strike rates are highest. Birds in this area breed in cultivated fields and pastures. The agricultural land can be managed to benefit the cranes and bustards in this altered landscape. In the Overberg, cranes avoid natural fynbos vegetation, preferring to inhabit cereal croplands and cultivated pastures because these resemble their natural grassland habitats. By contrast, they inhabit natural vegetation in the Karoo and Grassland biomes, but also feed in crop fields.
The indirect impacts from agriculture include the abstraction of water; the pollution of water with pesticides or fertilisers; the pollution of the environment with potentially harmful and persistent agrochemicals, specifically pesticides; the spread of alien invasive vegetation; the persecution of perceived problem animals; and incorrect burning regimes for the sensitive Renosterveld. All of these threats can potentially be mitigated through raising farmers' awareness, encouraging environmentally friendly farming practices and, where possible, purchasing land or signing conservation easements (voluntary title deed restrictions) with landowners.
The Cape Vultures from the breeding colony at De Hoop Nature Reserve forage outside the reserve structure and are vulnerable to the indiscriminate use of poison by small-stock farmers, who may put down poison for mammalian predators such as jackals and dogs. The farmers in this region are eager to contribute to conservation schemes, but it should be emphasised that a single poisoned carcass could decimate the entire colony.
There is relatively little protection in this IBA by means of formally protected areas. Some adjacent areas that have received formal protection are De Mond Nature Reserve and Agulhas National Park (both part of the Heuningnes Estuary–Agulhas Plain IBA), De Hoop Nature Reserve and Bontebok National Park. However, these do not constitute the major portion of the Overberg Wheatbelt IBA. More recently, 500 ha of Renosterveld located north of De Hoop Nature Reserve was secured by WWF-SA, in partnership with the Overberg Lowlands Conservation Trust, through land purchase. Stewardship options are currently being investigated to bring small portions (remnants of Renosterveld) of the IBA under some form of formal conservation designation. Landowner 'custodianship' or improved land-management practices on farms must also be considered because trigger species also occur in transformed landscapes.
The conservation actions within the Overberg Wheatbelt have been limited in extent and capacity. The two major interventions have been efforts to acquire Biodiversity Stewardship sites in order to secure remnants of Renosterveld vegetation; and the Overberg Crane Group's extension work with farmers, which has focused on building awareness of Blue Cranes on farms and reducing mortalities of this species. Much of the vegetation in the IBA is listed under NEMBA as 'threatened ecosystem', which gives it some degree of protection, although this has not been much of a deterrent against the continued (illegal) removal of these habitats.
With a focus on the threatened Renosterveld vegetation, Odette Curtis of the Overberg Lowlands Conservation Trust engaged in stewardship initiatives with certain landowners while she was working for CapeNature. Currently the Overberg Lowlands Conservation Trust, CapeNature and the new WWF-SA 'Better Barley, Better Beer' project are exploring additional opportunities for stewardship in the IBA, with an emphasis on the largest extant area of remnant Western Rûens Shale Renosterveld in the Bot River area. The Overberg Lowlands Conservation Trust is also pursuing the development of a Conservation Easement Programme with its partners, and it and BirdLife South Africa have signed an MoU regarding their shared work in this area. Their long-term vision is to create Renosterveld conservation areas through voluntary title-deed restrictions and to increase environmental awareness among landowners through the development and distribution of an information booklet about the fauna and flora of the Overberg region. The Overberg Crane Group has spent many years actively engaging farmers and other landowners to improve land management and attitudes for the benefit of Blue Cranes.
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