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Understanding urban raptor populations

With most of the world’s human population now living in urban areas, the impact of urbanisation on biodiversity continues to grow. Wildlife populations in urban areas may be affected by habitat loss and fragmentation, altered bio-geochemical cycles and the introduction of novel urban stressors such as light, noise and air pollution, nutritional changes, disease transmissions and novel predators like domestic pets. Within urban ecology, birds are perhaps the most well studied taxon. Some species thrive by exploiting human-subsidised resources, whereas others are unable to cope with habitat transformation and disturbance. As such, urban birds can be split into three groups – ‘urban avoiders’, ‘urban adapters’ and ‘urban exploiters’. However, whilst an urban-exploiting or adaptable species may be able to make use of abundant resources in the short-term, there may be other hidden costs of urban living which could undermine its long-term health and persistence in an urban environment.

By monitoring the Black Sparrowhawk Accipiter melanoleucus population in Cape Town we are exploring how a top avian predator copes with living in an urban environment. This population of raptors has been monitored since 2000, shortly after it started breeding in the area. The species can be characterised as an urban adapter, taking advantage of the availability of nesting trees in alien Eucalyptus and pine plantations and the high prey abundance of pigeons and doves that occur in parks and gardens. Although the species seemingly thrives in the city, we are interested to explore whether they suffer hidden health impacts or changes in their breeding performance compared to birds in more rural environments.

We are now expanding our research to include another urban nesting raptor – the Peregrine Falcon Falco peregrinus. The project led by Petra Sumasgutner, Arjun Amar, Res Altwegg and Andrew Jenkins will combine long term-data for both Black Sparrowhawks and Peregrine Falcons to understand the interplay between urbanisation and climate change and how it might affect our avian top-predators. Climate change is predicted to have a particularly high impact on the Cape Peninsula. Thus, our study with access to long-term data of individually colour ringed raptor populations provides an important model system to predict the impact of such changes.

Activities in 2016:

  • Jessleena Suri completed her CB MSc dissertation exploring whether there were any health issues for Black Sparrowhawk nestlings along an urban-rural gradient.
  • Sanjo Rose completed her Honours project investigating the timing of breeding and breeding performance of pairs along an urban-rural gradient.
  • In 2016, 52 Black Sparrowhawk territories were monitored with a 74% success rate of breeding pairs, which was higher than in previous years. In total 58 chicks fledged, of which 43 were colour ringed.
  • Petra Sumasgutner visited Lund University in May to establish a biomarker approach for the Black Sparrowhawk Project. These ecophysiological data were part of a pilot study on urban impacts on raptor health.
  • We presented our research at the Pan-African Ornithological Congress (PAOC), Dakar, Senegal; the International Society of Behavioural Ecology (ISBE), Exeter, UK; the North American Ornithological Conference (NAOC), Washington DC; and the British Ornithologist Union (BOU) conference on urban birds in Leicester, UK.

Highlights:

  • The urban raptor group was invited to contribute a paper for the research topic "Behavioural and Ecological Consequences of Urban Life in Birds" in Frontiers in Ecology and Evolution. The manuscript with Sanjo Rose as lead author was submitted in early 2017.
  • We received funding for a three year joint South Africa-Sweden Research Collaboration focusing on urban avian ecology by the NRF and STINT (Assoc. Prof. Caroline Isaksson, Lund University).
  • We organized the joint symposium “Birds as city slickers” with our collaborators from Lund University at the NAOC in Washington DC; and contributed a blog on how rapid urbanisation is changing the profile of wildlife in cities for The Conversation (African Edition).
  • Petra Sumasgutner was honoured with the early career research award for her talk Street-wise: polymorphism, productivity, health and prey of urban black sparrowhawks” at the BOU conference.
  • We published a paper in BMC Evolutionary Biology on how Black Sparrowhawks cope with breeding alongside Egyptian Geese who steal their nests (Sumasgutner et al. 2016).
  • We published a paper on the home range size of male Black Sparrowhawks using GPS tagged birds in Bird Study (Sumasgutner et al. 2016).
  • A paper based on Julia van Velden’s BSc Honours dissertation on knemidokoptes mite infections in Black Sparrowhawks was  accepted for publication in Auk.
  • Ann Koeslag completed her final year of monitoring the Black Sparrowhawk population. Ann has been instrumental in monitoring the Cape Peninsula population for over a decade. The project owes Ann a huge debt of gratitude.

Impact of the project

Our project represents one of the first to examine individual health and productivity of a bird species in relation to urbanisation in Africa. Our results have considerable implications for potential changes in phenology or productivity for the regions’ avifauna as African urbanisation continues.

Key co-sponsors

DST-NRF CoE grant; NRF-STINT South Africa-Sweden Research Collaboration, Claude Leon Foundation.

Research team

Dr Arjun Amar (FIAO, UCT)
Dr Petra Sumasgutner (FIAO, UCT)
Dr Res Altwegg (SEEC, UCT)
Dr Andrew Jenkins (ADU, UCT)
Ann Koeslag (Volunteer)

Students: Jessleena Suri (CB MSc, UCT), Sanjo Rose (BSc Hons, UCT)

Research Assistant: Mark Cowen