Urban refuge or ecological trap? Energy expenditure and space use of African crowned eagles in Durban

Urban expansion is reshaping ecosystems worldwide, yet a surprising diversity of wildlife persists in cities, offering unique opportunities, but also urgent challenges, for biodiversity monitoring. Among raptors, urban tolerance is typically restricted to small-bodied, generalist species, making the African crowned eagle (Stephanoaetus coronatus) – a large, powerful forest specialist – a notable exception. Despite being considered threatened in South Africa and commonly persecuted, crowned eagles reach higher densities within the Durban Metropolitan Open Space System (DMOSS) than in surrounding natural habitats. Durban may function as an urban refuge, offering abundant non-native eucalyptus trees for nesting and an assemblage of city-dwelling prey, including rock hyraxes, hadeda ibises, and vervet monkeys. Yet the mechanisms by which these apex predators persist in such a fragmented landscape – and the implications for biodiversity monitoring – remain poorly understood.

Here, we combined high-resolution GPS and triaxial accelerometry to quantify habitat selection and energy expenditure across urban areas. Using Resource Selection Functions and Overall Dynamic Body Acceleration as a proxy for energy expenditure, we show that crowned eagles expend substantially more energy in transformed habitats – particularly near DMOSS boundaries and roads – while forest patches serve as energetic refuges. Elevated energy expenditure may signal hunting activity or behavioural responses to human disturbance. Their movement trajectories capture fine-scale ecosystem processes that are otherwise not represented in conventional biodiversity assessments.

Our ongoing work extends this framework by tracking breeding pairs to map fine-scale hunting excursions, quantify sex-specific prey capture linked to pronounced sexual size dimorphism, and examine behavioural complementarity during offspring provisioning. These metrics are directly interpretable as movement traits with biodiversity relevance, informing: (1) functional connectivity within urban green networks; (2) predator–prey interactions and the persistence of urban trophic structures; and (3) the capacity of urban refugia to support apex predators.

By integrating movement-derived indicators into biodiversity monitoring workflows, this case study demonstrates how high-resolution biologging can reveal hidden ecological dynamics in cities and support evidence-based decision-making for urban biodiversity conservation at local and regional scales.