1 FitzPatrick Institute of African Ornithology, University of Cape Town, Cape Town, South Africa; Department of Zoology, University of Cambridge, Cambridge, UK. Electronic address: cns26@cam.ac.uk.
2 FitzPatrick Institute of African Ornithology, University of Cape Town, Cape Town, South Africa; Department of Zoology, University of Cambridge, Cambridge, UK.
3 FitzPatrick Institute of African Ornithology, University of Cape Town, Cape Town, South Africa.