John Shaw / Great frigatebird (Fregata minor) male at nest site, with gular sac inflated to attract females. Genovesa Island, Galapagos, May.

Glenn Bartley/ BIA / Streamertail (Trochilus polytmus) male feeding on flower nectar, Jamaica

Richard Du Toit / Red-billed Oxpecker (Buphagus erythrorhynchus) on Burchell's Zebra (Equus burchellii), Mkhuze Game Reserve, KwaZulu-Natal, South Africa

Richard Du Toit / Northern Giraffe (Giraffa camelopardalis) with Red-billed Oxpeckers (Buphagus erythrorhynchus) feeding on parasites in symbiotic relationship, Mkhuze Game Reserve, KwaZulu-Natal, South Africa

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.

Pete Oxford / White Rhinoceros (Ceratotherium simum) mother and calf with Red-billed Oxpeckers (Buphagus erythrorhynchus), South Africa

Biraj Sarkar/ BIA / Red-billed Leiothrix (Leiothrix lutea), Darjeeling, India

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.

Richard Du Toit / Red-billed Oxpecker (Buphagus erythrorhynchus) landing on South African Giraffe (Giraffa giraffa giraffa), KwaZulu-Natal, South Africa

Richard Du Toit / Red-billed Oxpecker (Buphagus erythrorhynchus) group on Warthog (Phacochoerus africanus), Kruger National Park, South Africa

Richard Du Toit / Red-billed Oxpecker (Buphagus erythrorhynchus) group on White Rhinoceros (Ceratotherium simum), Kruger National Park, South Africa