diagnostics
90-100 cm, 4.6-6.6 kg. Sexes alike. Head dark grey with whitish down. Neck dark blue-grey, with sparser down. Compact ruff at base of neck white. Crop patch brown. Contour feathers brown to off-white, and sometimes streaked. Diagnostic white lower back and rump visible when wings spread. Tail blackish brown. Upperwing coverts and remiges dark; underwing coverts buffy white. Bill and cere dark grey to black. Eyes dark brown. Legs and feet blackish grey. Immatures attain adult plumage over a period of six years. Juveniles are generally darker than adults, with thick woolly down on yellowish green head and neck, streaked body plumage and back spotted brown (instead of white).
The species is readily confused with the Cape Vulture G. coprotheres, especially when seen in flight and over distance. Seen close-up, the adult is easily differentiated from the adult Cape Vulture by its smaller size, dark eye, and black colour to the exposed skin on the head, neck and breast patches. Seen in flight from below, the adult has all-black remiges that contrast strongly with the pale underwing coverts. This species usually lacks the line of distinct dark spots along the greater upperwing, and along both the greater underwing and greater under primary coverts often present in the Cape Vulture. In flight, adult White-backed Vultures also often show a white rump when viewed from above. The more streaked juvenile and immature White-backed Vultures differ primarily from young Cape Vultures in the black colour of the exposed skin of the head, neck and breast patches, which are reddish in juveniles and immatures of the latter species. In flight, young White-backed Vultures typically show striking pale lines in the underwing coverts that are absent in young Cape Vultures (Mundy et al. 1992, Allan 2000, Ferguson-Lees and Christie 2001, Piper 2005).
trophic
The White-backed Vulture inhabits the woodland regions of southern Africa (Mundy et al. 1992, Mundy 1997). Its feeding and foraging habits are similar to those of the congeneric Cape Vulture and it relies primarily on large mammalian carcasses and feeds communally (Piper 2005). It is reported to very occasionally take live prey, e.g. young Springbok Antidorcas marsupialis and Warthog Phacochoerus aethiopicus (Mundy et al. 1992). This vulture is capable of long-distance movements, as evidenced by ring recoveries (Oatley 1998), re-sightings of marked birds (Monadjem et al. 2013) and GPS-GSM tracked birds (Phipps et al. 2013) but is not migratory (Mundy 1997, Piper 2005). Movements can be on a sub-continental scale and GPS-GSM tracked immatures made daily movements up to about 200 km (Phipps et al. 2013). White-backed Vultures typically roost in trees and on pylons (Mundy et al. 1992). Like the Cape Vulture, the White-backed Vulture drinks and bathes regularly (Mundy et al. 1992).
The breeding biology of the White-backed Vulture is fairly well known (Kemp and Kemp 1975, Mundy et al. 1992, Monadjem 2001, Monadjem et al. 2003, Herholdt and Anderson 2006, Tarboton 2011). The age of first breeding is four years, although birds only acquire full adult plumage in their 7th year. The species is monogamous. Unlike most other Gyps species, White-backed Vultures typically nest in tall trees and not on cliffs. Nesting on steel pylons has been recorded regularly in the Kimberley area (Northern Cape), Vryburg (North West), Marble Hall (Limpopo) and Boshof (Free State) (Ledger and Hobbs 1985, Wilson 2006, Anderson and Hohne 2008, de Swardt 2013). Nesting is typically loosely colonial, with pairs breeding within sight of one another, but usually with only one or sometimes two nests in a single tree. Where available, nests are typically concentrated in tall trees along watercourses (Bamford et al. 2009c). Nests are built of sticks and usually lined with grass. They are often re-used. The egg-laying period spans April-September, mainly April-July. The clutch almost invariably comprises a single egg, only very rarely are two eggs are recorded. Juveniles are partially dependent on their parents for food for 5-6 months after fledging. Breeding success is 43-87%. Nesting success is negatively correlated with nest density (Bamford et al. 2009c). The species is single brooded. Natural causes of breeding failure include predation of nestlings by Leopard Panthera pardus, Serval Felis serval and Honey Badger Mellivora capensis.
Annual survival in one South African study was found to be at least 85% in second-year birds to just less than 100% in adults, although the sample size (n=7) was small for the latter and overall the study was compromised by the fading of patagial tags after about 4-5 years (Monadjem et al. 2013). Natural sources of mortality include birds killed by Lion Panthera leo at carcasses and by Black-backed Jackals Canis mesomelas while drinking and bathing (Piper 2005, Herholdt and Anderson 2006).
