1. Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch, South Africa
2. Department of Mathematical Sciences, Stellenbosch University, Stellenbosch, South Africa; and African Institute for Mathematical Sciences, Cape Town, South Africa
3. Southern African Foundation for the Conservation of Coastal Birds, Cape Town, South Africa
4. Department of Biodiversity and Conservation Biology, University of the Western Cape, Bellville, South Africa