BEARDED VULTURE POPULATION AND HABITAT VIABILITY ...

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Population and Habitat Viability Assessment: Bearded Vulture (Gypaetus barbatus) ________________________________________________ 6. Life history Breeding: Presumably monogamous in southern Africa, and solitary (Mundy et al. 1992: 213- 215). Polyandrous trios have been recorded in Europe (Heredia and Donázar 1990) as well as solitary behaviour. In southern Africa three adults have been seen, on occasions, at the nests on Monks Cowl and Black Mountain in 2004 (S. Krüger pers. comm.) and at the Black Mountain nest in 2005 (S. Krüger pers. comm.; S.E. Piper, pers. obs.), though it is not known if these trios were made up of one female and two males. Average inter-pair distance = 6.3 km and min = 0.7 km in the high Drakensberg, 15 km in the Lesotho highlands and 19 km in the northern Eastern Cape Province, average breeding density is estimated at 1 pair/167.5 km 2 (Mundy et al. 1992: 215). Small exclusive breeding territory, ca 30 m in diameter, is maintained around nest only; however, Verreaux’s Eagles (Aquila verreauxii) are chased at 250 m (Mundy et al. 1992: 215). Most ‘courtship flights’ are initiated by the male who flaps up behind the female when she is gliding in the vicinity of the nest, this is followed for a few minutes by shallow undulations, either sex may lead (Mundy et al. 1992: 213). One bird flies upwards to a height and dives down to the other which rolls on its back and they engage talons: the diving bird calls shrilly (commonly observed among large raptors: Simmons and Mendelsohn 1993). Up to 14 such dives may occur. With talons locked they may fall through the air for a few hundred metres. Thereafter, they may land on a ledge and allopreen (Mundy et al. 1992: 214). Allopreening between partners is common, especially in the early morning and late afternoon (Mundy et al. 1992: 214). Copulation is preceded by a bout of allopreening, usually initiated by the male (Mundy et al. 1992: 214). They may also rub faces and heads together, sometimes the male bows a few times and even stamps his feet as if marching. The female stands next to the male slightly crouched before copulation that may take only a few seconds, occasionally they make a few soft high-pitched calls (Mundy et al. 1992: 214). Prebreeding courtship feeding has not been recorded. Nest: Males bring the sticks, carried lengthways, eagle-like, while females undertake the construction and help to provide the lining (Mundy et al. 1992: 215). They always nest on cliffs, usually in potholes or small caves, sometimes on ledges (Mundy et al. 1992: 214). In southern Africa nest sites on basalt cliffs average 195 m above ground and 2 814 m above sea level while those on sandstone average 47 m above ground and 1 935 m above sea level (Mundy et al. 1992: 214). The range of 74 nests in southern Africa was 24-732 m above ground and 1 850-3 200 m above sea level (Mundy et al. 1992: 214). The nests on exposed ledges were at lower altitudes and not susceptible to snowfalls. Pairs may have from one to eight alternative nests ranging from 2 m to 2 km apart, average = 230 m (Mundy et al. 1992: 214). Often use an alternative nest site each year, usually refurbishing an existing nest, 11
Population and Habitat Viability Assessment: Bearded Vulture (Gypaetus barbatus) ________________________________________________ possibly to starve out ectoparasites from the nest fabric (Simmons and Mendelsohn 1993: 215). However, this is not always the case, the Bearded Vulture nest on Black Mountain, near the Sehonghong River was used every year from 1993 to 2005, both years inclusive (R.D. Guy pers. comm.). Most nests receive no direct sunlight and are on the leeward side so that the parents can approach upwind (Mundy et al. 1992: 214). They construct a large nest of many twigs and branches (up to 1 m), average 1 m in diameter and 500 mm deep. Cup, with an internal diameter of ca 400 mm is copiously lined with wool, hair and skin (Mundy et al. 1992: 214-215). Unlike vultures (Gyps species), the nest site is largely unmarked by droppings (Mundy et al. 1992: 215). Laying dates: May (7), June (23), July (3) and August (1) (Mundy et al. 1992: 216 and RD Jeffery unpublished data), clearly autumn and early winter with pairs in the west (i.e. Maloti Mountains) laying nearly a month earlier than those in the east (i.e. Drakensberg) (Mundy et al. 1992: 216). Breeding is timed to synchronize the maximum food availability in September- October with the time of maximum food demand, when the nestling is growing fast and only 1 adult can leave the nest to forage (Mundy et al. 1992: 217). Eggs: 1-3 (1.7, n=38) (Maclean 1993,, RD Jeffery unpublished data), second egg laid 3-5 d after first (n=4), but interval can be up to 10 days (Mundy et al. 1992: 216). The egg is broadly oval in shape and rufous-orange in colour with a mottling of purple or reddish brown, some eggs paler or even whitish. Eggs have a rough shell that acquires iron oxide colouring from incubating adults so that they become darker with time (Mundy et al. 1992: 215). Size (n=27) 86.3-95.5 x 62.8-68.5 mm (86.9 x 65.4 mm) (Maclean 1993; RD Jeffery unpublished data; Northern Flagship Institution (= Transvaal Museum, in old speak); Steyn 1982). These data come from both South Africa and Kenya and need to be unpacked. Second egg in clutch is smaller by 4 mm in length and 3 mm in width (n=2) (Mundy et al. 1992: 215). Mass (n=2, G. b. barbatus, Europe) 242 g, i.e. ca 4% of ad mass, thus clutch of 2 is 8% (Mundy et al. 1992: 215). Pairs breed at most once a year and replacement clutches are unrecorded Mundy et al. 1992: 216). Incubation: Starts with first-laid egg, presumably to prevent it dying of cold (Mundy et al. 1992: 216). The incubation period is 56-58 days; by both sexes during the day, female only at night, female incubates ca 75% of time (Mundy et al. 1992: 216). Incubating adults sit tight but rise up ca once per hour to turn egg. A change-over occurs approximately once every 2.5 hr, and is quick and ‘stealthy’ and egg(s) are left exposed for less than 2 minutes (Mundy et al. 1992: 216). Males are more ‘restless’ when incubating. Incoming bird may bring new nest 12
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