Temporal changes in prey composition and biomass delivery to African Crowned Eagle nestlings in urban areas of KwaZulu-Natal, South Africa

Globally urban areas are expanding rapidly and this usually has negative effects on biodiversity. Despite this, some species manage to persist in urban areas, as is the case with African Crowned Eagles Stephanoaetus coronatus in KwaZulu-Natal, South Africa. As relatively little is known about African Crowned Eagle nestling diet, especially about how it changes with nestling age, we investigated this with nest camera-traps. We analysed temporal changes in prey composition and biomass delivery during the nestling stage. We also recorded which adults provisioned and attended the nest. The main prey fed to nestlings were Rock Hyrax Procavia capensis and Hadeda Ibis Bostrychia hagedash. Adult males did most of the food provisioning, especially at the start of the nestling period. We found a decrease in total prey number and biomass with nestling age. This may be caused by changing requirements of nestlings. Furthermore, delivering fewer prey at later nestling stages may be a facilitating mechanism to enhance fledging of the nestling. Although the total number of prey brought to the nest decreased, we found an increase in numbers of Vervet Monkey Chlorocebus pygerythrus in the diet with nestling age. This indicated an increase in larger prey being delivered to the nests as the nestling aged. We suggest that this could be caused by increased participation in hunting by the larger female as her nest attendance time decreased as the nestling aged. We conclude with emphasising the importance of protecting the Durban Metropolitan Open Space System (D’MOSS) zones for the persistence of this Near Threatened raptor species, and populations of its prey in urban areas for its breeding success.

全球范围内城市区域正快速扩张，这通常会对生物多样性造成负面影响。尽管如此，仍有部分物种能够在城市区域存续，南非夸祖鲁-纳塔尔省的非洲冕雕（African Crowned Eagle, Stephanoaetus coronatus）便是一例。由于目前对非洲冕雕雏鸟的饮食组成，尤其是其随雏鸟龄期变化的规律所知甚少，我们借助巢穴相机陷阱开展了相关研究。我们分析了雏鸟期内猎物组成与猎物生物量投喂的时间动态变化，同时记录了参与食物投喂与巢穴值守的成鸟个体。雏鸟的主要猎物为岩蹄兔（Rock Hyrax, Procavia capensis）与哈达朱鹭（Hadeda Ibis, Bostrychia hagedash）。雄成鸟承担了绝大多数的食物投喂工作，尤其在雏鸟期初期阶段。我们发现，随着雏鸟龄期增长，投喂的猎物总数量与总生物量均呈下降趋势，这可能与雏鸟的营养需求变化有关。此外，在雏鸟期后期减少猎物投喂量，或许是一种促进雏鸟成功离巢的适应性策略。尽管投喂至巢穴的猎物总数量有所下降，但我们发现，雏鸟饮食中的黑长尾猴（Vervet Monkey, Chlorocebus pygerythrus）占比随雏鸟龄期增长而上升，这意味着随着雏鸟长大，投喂的大型猎物占比有所提升。我们推测，这一现象可能是由于：随着雏鸟龄期增长，体型更大的雌成鸟的巢穴值守时间减少，其参与狩猎的频次随之增加。最后我们着重强调：保护德班都市开放空间系统（Durban Metropolitan Open Space System, D’MOSS）区域，对于维持这一近危猛禽物种的种群存续至关重要；同时保护城市区域内的猎物种群，亦是保障该物种繁殖成功的关键。