Conservation priorities for the Blue Crane (Anthropoides paradiseus) in South Africa - the effects of habitat changes on distribution and numbers

摘要

Detailed knowledge on population numbers, habitat preferences and threats is lacking for the Blue Crane (Anthropoides paradiseus), which is endemic to southern Africa and is South Africa's national bird. Using the South African Bird Atlas Project BlueCrane distribution as the accepted distribution of the species, this analysis has shown three distinct core areas for the population determined by a core index value. The largest of these core areas occurs in the central Karoo region covering 153 153 km~2. The next largest core area was in the Eastern Grassland region covering 137 838 km~2. The final core area is located in the areas known as the Overberg and Swartland of the Western Cape province, encompassing 23 440 km~2. The annual National Crane Census in South Africa, which covered 40% of the Blue Crane's distribution, has resulted in the determination of the actual minimum population size of 25 520 individuals. An assessment of the Blue Crane's distribution in relation to the vegetation composition of the three core areas shows that it has experienced a dramatic decline in population numbers in the Eastern Grasslands core area, where a significant degree of grassland transformation and fragmentation has occurred. The Central Karoo population has remained stable and comprises 42.4% of the current national population estimate. More than 42% of this core area comprises Nama Karoo vegetation with little habitat transformation. The most significant change has occurred in the Western Cape, which historically consisted of unsuitable Blue Crane habitat. The conversion of Fynbos and Renosterveld to 'artificial grasslands' through agricultural developments has created a favourable habitat for Blue Cranes, with this core area, comprising only 7.6% of the total core area in the country, having 47.4% of the national population. The conservation of the Blue Crane in these core areas relies on private landowners implementing management plans that allow the Blue Crane to coexist in an agricultural landscape. Knowledge through applied research will allow the identification of preferred habitats, breeding locations and suitable management activities. The landscape approach of conservation allows the benefits of ecosystem management to be realised for both people and the biodiversity elements.