Loon, Rael & Loon, Hélène (2005): Birds. The inside story. Bird Biology and Behaviour in Southern Africa. Cape Town, South Africa: Struik Publishers. ISBN 1-77007-151-2, páxina 183. Amplo resumoArquivado 19 de febreiro de 2015 en Wayback Machine..
Loon, Rael & Loon, Hélène (2005): Birds. The inside story. Bird Biology and Behaviour in Southern Africa. Cape Town, South Africa: Struik Publishers. ISBN 1-77007-151-2, páxina 183. Amplo resumoArquivado 19 de febreiro de 2015 en Wayback Machine..