BEARDED VULTURE POPULATION AND HABITAT VIABILITY ...

Population and Habitat Viability Assessment: Bearded Vulture (Gypaetus barbatus)
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stage, is much more likely to fly off; an immature which is more dependent on large carcasses,
is more likely to stay and in turn be joined by other immature birds (Mundy et al. 1992: 211).
Bearded Vultures of all ages give way to Cape Griffon Vultures of all ages and adult
Verreaux’s Eagles but are not intimidated by immature Verreaux’s Eagles (Mundy et al. 1992:
211). Food consists mainly bones from both fresh and old carcasses and given a choice they
prefer bone to fresh meat (Mundy et al. 1992: 212-213) but they require red meat to feed
nestlings (Brown 1997b). They are well-adapted to handle and process bones, including a
wide gape of ca 70 mm which allows bones of up to 250 mm long by 35 mm in diameter to be
swallowed, and digestion can proceed with part of the bone sitting in the throat or even still
protruding from the mouth (Mundy et al. 1992: 212). Digestive juices are very acidic, probably
with a pH of ca 1.0-1.5 (Mundy et al. 1992: 212). They are able to disarticulate bones from
skeletons by tearing or cutting tendons and ligaments using the bill, and thus able to utilise
completely dried-out carcasses (Mundy et al. 1992: 212). They are able to fly with large bones
held parallel to the body, and process it at its leisure elsewhere. The heaviest bone removed
was 4.3 kg, i.e. ca 69-83% of its body weight (Mundy et al. 1992: 212). The most famous
adaptation, earning the name Ossifrage, is their ability to carry a bone aloft and drop it on an
ossuary or ‘rock anvil.’ The average size of nine ossuaries in southern Africa was 1 600 m 2 ,
i.e. a diameter of 44 m (Mundy et al. 1992: 212). Gliding downwind at ca 56 m (range 16-70
m) above ground, the bird steepens its glide, lowers its feet, drops the bone and then turns
into the wind and descends and lands in a fluttery way (Mundy et al. 1992: 212), a technique
that has to be learnt by immature birds (Mundy et al. 1992: 212). Bones are dropped an
average of six times to 21 times (Mundy et al. 1992: 212). Breaking large bones reduces them
to more manageable pieces and exposes the marrow. The long protrusible tongue, which is
grooved but smooth along the edges is presumably used to scoop out marrow from bones and
brains from skulls. The average diet is 70% bone, 25% fresh meat and 5% skin (Mundy et al.
1992: 212-213). The most identifiable food items brought to the nest in southern Africa are
from domestic stock, especially sheep and goats but also from cattle (Mundy et al. 1992: 218).
Afterbirths from sheep are also eaten (Mundy et al. 1992: 213). Estimated food consumption
465 grams food per day, ca 8% of body mass, which they try to consume every day, avoiding
the feast and famine strategy of vultures (Gyps species) (Mundy et al. 1992: 213). Breeding
adults form caches of food items, especially bones in potholes near their nests (Brown 1997b;
Mundy et al. 1992: 216). Competition with other birds for food is rare; only one record known
of a presumed adult Verreaux’s Eagle pirating meat from a Bearded Vulture (Scotcher 1973).
Competition with scavenging mammals exists, currently most likely with domestic dogs and
Black-backed Jackals Canis mesomelas, but probably with Spotted and Brown Hyaenas
Crocuta crocuta and Hyaena brunnea in the past. It does not compete with White-necked
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