Guy Edwardes / Red-billed oxpecker (Buphagus erythrorhynchus) feeding on Impala (Aepyceros melampus), Savuti, Botswana.

Ann & Steve Toon / Impala (Aepyceros melampus) with redbilled oxpecker (Buphagus erythrorhynchus), Kruger National Park, South Africa.

Neil Aldridge / Red-billed oxpeckers (Buphagus erythrorhynchus) adult and young on the back of Common warthog (Phacochoerus africanus) through grassland in summer Mapungubwe National Park, South Africa.

Ann & Steve Toon / Warthog (Phacochoerus africanus) with Redbilled oxpecker (Buphagus erythrorhynchus), Zimanga game reserve, KwaZulu-Natal, South Africa.

Ann & Steve Toon / Warthog (Phacochoerus africanus) drinking, with redbilled oxpeckers (Buphagus erythrorhynchus), Zimanga game reserve, KwaZulu-Natal, South Africa.

Ann & Steve Toon / Warthog (Phacochoerus africanus) drinking, with redbilled oxpecker (Buphagus erythrorhynchus), Zimanga game reserve, KwaZulu-Natal, South Africa.

Ann & Steve Toon / Redbilled oxpecker (Buphagus erythrorhynchus) searching for insects on Warthog (Phacochoerus africanus), Zimanga game reserve, KwaZulu-Natal, South Africa.

Ann & Steve Toon / Redbilled oxpecker (Buphagus erythrorhynchus) drinking from perch on warthog, Zimanga private game reserve, KwaZulu-Natal, South Africa.

Melvin Grey / Cape buffalo (Syncerus caffer caffer) portrait, Red-billed oxpeckers (Buphagus erythrorhynchus) removing parasites. Nakuru, Kenya.

Staffan Widstrand / Common Warthog (Phacochoerus africanus), with a Red-billed Oxpecker (Buphagus erythrorhynchus) eating its ticks and other parasites, Zimanga Private Nature Reserve, KwaZulu Natal, South Africa

Staffan Widstrand / Common Warthog (Phacochoerus africanus), with a Red-billed Oxpecker (Buphagus erythrorhynchus) eating its ticks and other parasites, Zimanga Private Nature Reserve, KwaZulu Natal, South Africa

Ann & Steve Toon / Redbilled oxpecker (Buphagus erythrorhynchus) on Impala (Aepyceros melampus), iMfolozi game reserve, KwaZulu-Natal, South Africa, September