Open image gallery
The regional population of Karoo Korhaan Eupodotis vigorsii is suspected to have undergone a population decline approaching 30% over the last 10 years. The cause of this reduction is not perfectly understood. The species is assessed as regional Near Threatened pending further population trend data.
Endemic to the xerophytic dwarf shrublands of the Karoo Biome in western South Africa and southern Namibia (Hockey and Boobyer 1994, Allan 1997g). Within the region, occurs from the western Free State and near the Great Fish River Estuary in Eastern Cape (Tree 1973), westwards across the arid interior of Western Cape and Northern Cape provinces and north to the Orange River. Since at least the 1860s, has extended into agricultural areas on the Agulhas Plain, Western Cape, where it occurs in bare fallow wheat lands and planted pastures but is scarce or absent in adjacent remnant patches of Renosterveld (Uys 1981, Allan 1997g). Extends into the Karoo-Grassland biome ecotone in the east of its range, but replaced in higher rainfall grasslands by the Blue Korhaan E. caerulescens (Hockey and Boobyer 1994). The limits of its distribution in southern Namibia are unclear as it was previously considered conspecific with Rüppell's Korhaan (Allan 1997g). SABAP2 data suggests an AoO of c. 166 000 km2.
The global population size is unknown, but Siegfried (1992) estimated the South African population to be ‘hundreds of thousands'. Population densities have been measured at 1 group/0.5-3.3 km2, with territories being the largest in more arid areas. Likewise, average group size is higher in drier areas: average 2.24 birds in the arid Succulent Karoo, 2.19 in Nama Karoo, and 2.09 on Agulhas Plain (Allan 2005i); larger groups may be beneficial in terms of territorial defence, foraging efficiency or vigilance against predators (Hockey and Boobyer 1994). Mostly encountered in pairs (72%), but male and female are regularly accompanied by 1 (16%) or 2 (3%) additional birds, mostly male offspring; rarely seen alone or in groups of 5-6 birds (Hockey and Boobyer 1994). Based on data of Hockey and Boobyer (1994) and Allan (2005i), a coarse extrapolation of average group size and average group territory size divided by the regional AoO, suggests that the total South African population may lie in the order of c. 250 000 birds. Confidence in this estimate is low.
A comparison of SABAP1 and SABAP2 data suggests the Karoo Korhaan has undergone an alarming c. 50% decrease in AoO, which is of particular concern as the majority of its global range falls within South Africa. However, the reasons for this apparent contraction are unclear and warrant investigation. The species was not considered threatened by Brooke (1984) or Barnes (2000a). Anecdotal historical accounts suggest that the species may have increased in abundance, possibly as a result of its ability to exploit habitats modified by pastoralism over the past 150 years (Boobyer and Hockey 1994). Its colonisation of cereal croplands in the Overberg region also suggests a degree of adaptability to disturbed habitats. Nevertheless, a bustard conservation workshop in 2009 identified the Karoo Korhaan as subject to a high perceived level of threat. Confidence in this estimate is low.
Power-lines, climate change, and impact of poisons used during locust-control operations are general threats faced by the Karoo Korhaan (Allan and Anderson 2010). Farming activities pose a local threat to eggs and small chicks in agricultural areas, such as on the Agulhas Plain (Uys 1981). Crows are recorded as frequent nest predators (Uys 1981), and increasing abundance of crows may have a local impact on breeding success in some areas. The species is preyed upon by large eagles, and is the most common prey item of Martial Eagles in the Karoo (Boshoff et al. 1990).
No species-specific conservation efforts are underway.
While the Karoo Korhaan remains relatively common and widespread, atlas data suggest that an overlooked decrease in range and population might be occurring. The causes for this apparent decline are not fully understood and should be assessed so that appropriate conservation measures can be implemented if necessary.
* The threats responsible for the rapid decline in this species should be urgently investigated and their relative severity and predicted outcomes should be assessed.