Browsing by Author "Krüger, Sonja"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Open Access
    Differential range use between age classes of southern African Bearded Vultures Gypaetus barbatus
    (Public Library of Science, 2014) Krüger, Sonja; Reid, Timothy; Amar, Arjun
    Bearded Vulture Gypaetus barbatus movements were investigated in southern Africa to determine whether an individual's age, sex or breeding status influenced its ranging behaviour and to provide the information required to guide conservation activities. Data from satellite transmitters fitted to 18 individuals of four age classes were used to determine range size and use. Because of the nature of the movements of marked individuals, these data could be used to determine the overall foraging range of the entire population, which was estimated to be 51 767 km 2 . Although juvenile, immature and sub-adult birds used different parts of the overall range, their combined foraging range was 65% (33 636 km 2 ) of the overall range. Average adult home ranges (286 km 2 ) were only around 1% the size of the average foraging ranges of non-adults (10 540 -25 985 km 2 ), with those of breeding adults being even smaller (95 km 2 ). Home ranges of breeding adults did not vary in size between seasons but adults utilized their home range more intensively whilst breeding, moving greater distances during the incubation and chick hatching period. Range size and use increased as non-adults aged. Immatures and sub-adults had larger range sizes during winter, but range use of non-adults did not vary seasonally. Range size and use did not differ between the sexes in any of the age classes. Information on home range size and use enables specific areas within the species' range to be targeted for management planning, education and conservation action.
  • Thumbnail Image
    Item
    Open Access
    Habitat selection of adult bearded vultures Gypaetus barbatus in southern Africa: implications for conservation
    (2021) Sheik Abbass, Mohammad Imthiaz Zulfur Ali; Amar, Arjun; Murgatroyd, Megan; Krüger, Sonja
    The Bearded Vulture, Gypaetus barbatus, was previously distributed across southern and western South Africa, as far south as Cape Town. Today, the entire population in southern Africa is restricted to the Lesotho highlands and the Drakensberg escarpment and nearby mountains in South Africa, where the population continues to decline. Research has shown that territorial abandonment is apparently associated with the density of human settlements within 10km of a territory. This pattern was assumed to be linked to the increased risk of unnatural mortalities in areas with higher human presence. However, habitat use and habitat selection, especially whether the species actively avoids human settlements has not yet been explored and could contribute to this pattern. In this study, we used data from nine adult Bearded Vultures fitted with Global Positioning System (GPS) satellite tags to determine which habitat is being selected. We modelled habitat selection in relation to various topographic and habitat variables, including information on built-up areas (i.e., areas with a high density of buildings). We predicted that birds would select areas of grassland and avoid areas with high building density and adjoining areas. We found that Bearded Vultures selected areas closer to their nest sites and supplementary feeding sites, with steeper slopes, and highly rugged terrain. In terms of habitat, they selected areas with grassland and avoided areas with forest, while cropland was neither selected nor avoided. As predicted Bearded Vultures avoided built-up areas and their vicinity. These results suggest that the Bearded Vulture may be sensitive to the negative impacts of a changing landscape in its distribution range. These results can help conservation managers in guiding development (e.g., human settlement expansion and afforestation) and protecting priority habitats (e.g., grassland) within the breeding range of adult Bearded Vultures.
  • Thumbnail Image
    Item
    Open Access
    The reintroduction of bearded vultures in South Africa: a feasibility analysis
    (2016) Brink, Christiaan Willem; Amar, Arjun; Krüger, Sonja
    The southern African population of bearded vultures, Gypaetus barbatus, is declining rapidly and plans for windfarm developments within the core of this species' range threaten to accelerate the population's passage to extinction. As an insurance against such a situation a reintroduction has been proposed to establish a second bearded vulture population within their historic South African range. Before such a scheme could occur suitable areas, if present, will first need to be identified and the requirements and best implementation strategy will need to be determined. Therefore, the aims of this study were (1) to identify the most suitable site for such a reintroduction and (2) to provide some insight into the potential outcomes of different release strategies. Habitat modelling and GIS techniques were used to identify potential reintroduction sites, most notably based on the presence of cliffs. Potential reintroduction sites were then compared based on a range of habitat attributes, of which the amount of human settlement and power line density was considered most important. Five potential reintroduction sites were identified with the two highest ranking sites situated mostly within the Eastern Cape Province. Various release strategies ranging from captive breeding prioritization to release prioritization were modelled using stochastic modelling software. Results indicated that straight releases, without any captive breeding support, had a high probability of failure (defined <34 individuals) ranging between 78.3 and 95.7% across different mortality scenarios over a 30 year period. Supplementation from captive breeding reduced this to between 25.5 and 49.8%. Although it is important for mortality rates to be lower at the reintroduced site this study shows that a reintroduction initiative can be valuable even if this is not the case, as a reintroduction initiative can reduce the probability of extinction (one sex remains) of the species in southern Africa after 50 years by approximately 30%. This study concludes that a captive breeding programme is imperative for the success of the reintroduction and is a prudent measure considering the continuing decline of the species. However, a complementary study examining release sites on the ground as well as stakeholder attitudes and the socio-economic impacts of bearded vultures will be required before the reintroduction can be implemented.