1. Department of Biological Sciences, University of Cape Town, Cape Town, South Africa
2. FitzPatrick Institute of African Ornithology, Department of Biological Sciences, University of Cape Town, Cape Town, South Africa
3. Centre for Functional Biodiversity, School of Life Sciences, University of KwaZulu-Natal, Scottsville, South Africa
4. BirdLife South Africa, Johannesburg, South Africa
5. Statistics in Ecology, Environment and Conservation, and Department of Statistical Sciences, University of Cape Town, Cape Town, South Africa