Distribution and abundance
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Widespread throughout suitable woodland savannas of sub Saharan Africa, the White-backed Vulture is probably Africa's most abundant vulture (Mundy et al. 1992). It is less widespread than the Lappet-faced Vulture but is almost certainly more abundant because of its colonial nature. African populations have been estimated at 270,000 individuals (Mundy et al. 1992) with c. 40,000 individuals (15%) in southern Africa (Anderson 2000, Anderson 2004). Its core areas are the Kruger NP, and the northern border of South Africa from the Northern Cape eastwards, most of Zimbabwe, Botswana and all but the un-treed areas of Namibia (Mundy 1997). Core areas include Etosha NP and the Caprivi Strip, but it is still common throughout the central and southern parts of Namibia.
There is one estimate of Namibian populations of 6000 prs (Simmons in Anderson 2004). Two comparisons using population densities from the former Transvaal (of 2,600 prs in 400 QDS: Tarboton & Allan 1984, Harrison et al.1997) and Swaziland (300 prs in 24 QDS: Monadjem et al. 2003) suggest that Namibia's population which occupies an area of 305,272 km2 (Jarvis et al. 2001) approximately 1.12 fold and 18.6 fold larger than the Transvaal and Swaziland populations, respectively, gives estimates for Namibia of about 2,900 prs - 56,00 prs. Using a factor of 2.7 to convert from prs to individuals (Mundy et al. 1992, Murn et al. 2002), gives an estimate of 7,830- 15,050 birds for Namibia. Because Swaziland breeding colonies are known to be particularly dense (A Monadjem pers obs), the Namibian population probably lies towards the lower end of this range, approximately 10,000 birds or 25% of the southern Africa's total population. This requires a more rigorous assessment and may prove higher than this figure suggests (D Joubert pers comm). One recent aerial survey indicates that a colony near the Waterberg Plateau occurred at a density of 3.8 nests/10 km2 (Doulton & Diekmann 2006), as predicted at the lower end of the breeding density found in Swaziland.
Road counts in Etosha and other arid regions of Namibia varied from 0.1 birds/1,000 km to 146 birds/1,000 km driven (Jarvis et al. 2001), considerably higher than any of the other vultures.
Prefers the drier tall-tree savannas of southern Africa, particularly in Botswana's and Namibia's Kalahari Sand and mopane woodland belts (Mundy 1997). In Namibia it is found most abundantly in Etosha and regions to the n-e where prey populations of large ungulates are intact in Etosha NP (Mundy 1997). The tallest trees are used for breeding and roosting purposes (Mundy et al. 1992). Breeding occurs in the winter with egg-laying recorded from March (1), April (8), May (6), June (21), July (11) (Brown & Clinning unpubl data). Additional breeding data is surprisingly non-existent for Namibia so success of colonies is unknown.
Feeds by scavenging from carcasses of both large and small indigenous mammals and domestic livestock, and is most often seen feeding in large noisy flocks at large carcasses in protected areas or at vulture restaurants (Steyn 1982, Mundy et al. 1992).
Like other vultures this species suffers from continuous poisoning both in Namibia (Simmons & Bridgeford 1997, Bridgeford & Simmons unpubl) and elsewhere (Mundy et al. 1992, Anderson 2000). The poisoning rate for this species was 41 birds in the 7 yr period 1995-2001, second only to the Lappet-faced Vulture (Bridgeford & Simmons unpubl data). Poisoned birds are found from southern Namibia to areas just outside the Etosha and Waterberg Plateau parks. They include nestlings hatched inside the Etosha NP (T Osborne, W Versfeld, pers comm.). Curiously White-backed Vultures still occur in the small-stock farming areas in southern and central Namibia where poisoning of small carnivores is common (Brown 1988, Brown 1991). This suggests either (i) that poisoning alone is not responsible for population declines and other factors such as food resource levels explain the demise of other vultures (Boshoff & Vernon 1980, Anderson 2000) or (ii) poisoning is decreasing in Namibia (unlikely: Komen 2002) or (iii) this species is a prolific breeder and the sink areas are rapidly re-populated with recruits from source areas away from poisons.
Of these a declining food base due to (i) overall degradation of the environment, (ii) bush encroachment over large parts of its stronghold in central and n Namibia (Mendelsohn et al. 2002) and (iii) a decline in prey base due to better or alternative farming methods is the most likely cause (Boshoff et al. 1997). Central farming land where this species is most widespread has changed shape over the last 100 year. For example farmed land has risen from 48,000 km2 in 1902 to (more-intensively) farmed agricultural land of 356,000 km2 in 2002. Areas in former Ovamboland where the bird almost certainly occurred 100 yrs ago have been almost completely cleared for crop cultivation (Mendelsohn et al. 2002), leaving few records of vultures over the last 20 years (Mundy 1997).
Electrocutions are often mentioned as a major cause of the slow decline in this species (van Rooyen 2000), and Namibia has thousands of kilometers of powerlines that are unfriendly to vultures (Brown & Lawson 1989). Yet the evidence that lines actually kill a substantial number of birds here is scant. There are just two records of injury/electrocution from farms n-e of Windhoek (P Bridgeford unpubl data). The low frequency may arise because power lines are not systematically searched, or birds killed are missed because they are quickly scavenged. It is unlikely that vultures act differently in Namibia to South Africa, (although the density of power lines is higher in South Africa than Namibia: C van Rooyen pers comm) so we conclude that it is under-reported rather than a non-existent problem.
A more recently identified potential problem for Gyps vultures is the use of drug Diclofenac. The use of this drug in India for the treatment of cattle has decimated vulture populations there (Oaks et al. 2004). Its apparent use in southern Africa by veterinarians (M Anderson pers comm) could be a minor threat if used unchecked. Its level of use is unknown however.
Drowning in farm reservoirs is commonly reported in arid areas of South Africa (Anderson et al. 1999), where White-backed Vultures were ranked third among all species drowned. Several cases are known in Namibia (Bridgeford 2001, 2002, Bridgeford & Simmons unpubl data), but the level is probably low.
Use by traditional healers of nestling or adult birds is probably high for this species in Namibia, with about 48% of 17 healers indicating they use body parts such as brain, skull, heart and eyes from birds that they kill themselves or obtain from birds that have been killed (Hengari et al. 2004). The number of birds actually taken per year has yet to be determined.
While nest disturbance, cited as a problem in South Africa (M Anderson in litt), has not been reported as such in Namibia, the taking of nestlings and the high visibility of White-backed Vulture colonies makes them prime targets for disturbance.
This species is classified as Near Threatened because despite a suspected long term decline of 10-20% and degradation of prime habitat over the last 100 yrs, there is some evidence that birds are increasing outside Etosha NP boundaries (T Osborne in Anderson 2004) and from increasing numbers at vulture restaurants in the Waterberg area (M Diekmann pers obs). Outside Namibia populations or breeding areas have also increased on Zimbabwe's highveld (P Mundy in Anderson 2004), in Swaziland (Monadjem et al. 2003) and in the Northern Cape, South Africa (Murn et al. 2002, Anderson 2004).
It is not classified as globally threatened because of its wide distribution throughout Africa's wooded savannas (Birdlife International 2004). In South Africa it is classified as Vulnerable based on a suspected 10% decline (Anderson 2000), probably also as a result of poisoning associated with problem animal control operations and harvesting for traditional medicines. It is given the same Near Threatened status in Swaziland as designated here (Monadjem et al. 2003).
Decreasing the incidence of poisoning is paramount in preventing further population declines in all species of vulture. There are several ways of doing so which are discussed under Lappet-faced Vulture. The draft Parks & Wildlife Management Bill (2002) will ban the use of poisons in predator control, and permits are required from the Ministry of Environment & Tourism for farmers to use poisons in exceptional cases. Networks of vulture restaurants in areas known to be impacted by poisons can alleviate the problem of contaminated foods but may make vultures too dependent on man-provisioned food.
The extent of drowning in farm reservoirs should be investigated and education to alleviate this problem instigated by the Ministry of Environment and conservation organizations such as NARREC and REST.
Knowledge of the breeding of this species is virtually unknown in Namibia, despite monitoring projects. However in 2003 and 2004, 66 nestlings were ringed in the Seeis, Hochveld and Steinhausen areas (P Bridgeford, D Hienrich unpubl data). Numerous other hunting farms in these central-east regions have informal restaurants supporting numerous breeding birds (P Bridgeford pers obs). Such data should be published and future monitoring should assess breeding densities and the success of pairs breeding in them. Future population estimates require breeding density estimates from several areas and the extent that poisoning actually impacts populations in Namibia. Research including regular surveys of power lines near vulture colonies is required to determine the extent of the vulture collision and electrocution problem. Liaison with Nampower officials who regularly fly these lines would assist logistically. Where problem lines are identified, appropriate modifications or mitigation measures must be enacted.
From: Simmons RE & Brown CJ 2006. Birds to watch in Namibia: red, rare and endemic species. National Biodiversity Programme, Windhoek, Namibia
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