Just before and during the incubation of an egg or a clutch of eggs, a parent bird usually develops an incubation patch (= brood patch) in the skin over its sternum, or ventral side of its body. This is a featherless zone or apterium, devoid of both contour and downy feathers, and which develops many blood vessels for the transfer of body heat to the egg(s) (Proctor & Lynch 1993). Some few families of birds lack incubation patches, in others both sexes incubate and both partners have the patches (Skutch 1976). Among raptors there are those species where only the female incubates, those where the male may also incubate for short to longer periods, and those in which females and males equally share the incubation (Newton 1979). It is well known that both sexes incubate the clutch in vultures, both in the wild (Mundy et al. 1992) and in captivity (Mendelssohn & Leshem 1983). One pair of Cape Griffons Gyps coprotheres at the VulPro facility close to Hartebeespoort Dam (NW province), South Africa, was seen copulating in May to July and a single egg was laid. Unfortunately it broke. A second (replacement) was laid on 25 June.