Ann & Steve Toon / Ostrich (Struthio camelus) male standing in landscape, Table Mountain National Park, Western Cape, South Africa

Hougaard Malan / Ostrich (Struthio camelus) pair and chicks on dune in the Kalahari. Kgalagadi Transfrontier Park, Southern Africa, February.

Eric Baccega / Male Ostrich (Struthio camelus) protecting chicks from the sun with its wings, Samburu National Reserve, Kenya, Africa.

Denis-Huot,Denis-Huot / Ostrich (Struthio camelus) female and male with chicks, Masai-Mara Game Reserve, Kenya

Denis-Huot,Denis-Huot / Ostrich (Struthio camelus) female portrait, Masai-Mara Game Reserve, Kenya

Konrad Wothe,Konrad Wothe / Greater Rhea (Rhea americana) male, Pantanal, Brazil, South America

Tui De Roy / Stewart Island Brown Kiwi or Southern Tokoeka (Apteryx australis lawryi), female probing by scent for sand hoppers in rotting kelp beach wrack at night, Ocean Beach, Stewart Island, New Zealand

Tui De Roy / Okarito Brown Kiwi (Apteryx rowi) feather detail resembling mammalian hair. Okarito Forest, Westland, South Island, New Zealand.

Nick Garbutt / Lesser rhea (Rhea pennata) male and chicks in grassland. Torres del Paine National Park, Patagonia, Chile. November.

Gabriel Rojo / Greater rhea (Rhea americana) eggs in nest, at edge of arable field. Patagonia, Argentina. October.

Gabriel Rojo / Greater rhea (Rhea americana) nest with many eggs, at edge of arable field. Patagonia, Argentina. October.

Ingo Arndt / Hummingbird (Trochilidae) egg and Ostrich (Struthio camelus) egg, a size comparison of eggs of world's smallest and largest extant birds. Senckenberg Museum, Frankfurt, Germany.