Donald M. Jones / Black-tailed Prairie Dog (Cynomys ludovicianus) pair greeting, South Dakota

Will Burrard-Lucas / Black and white image of African elephant (Loxodonta africana) bulls males facing off against each other, Tsavo Conservation Area, Kenya. Editorial use only.

Ashley Cooper / Sun rays reflected onto solar tower at Ivanpah Solar Thermal Power Plant, the largest solar thermal plant in the world. It covers 4,000 acres of desert and produce 392 megawatts (MW) of electricity....

Alan Murphy/ BIA / Great Kiskadee (Pitangus sulphuratus) and Green Jay (Cyanocorax yncas) fighting, Texas

Thomas Hinsche/ BIA / European Bee-eater (Merops apiaster) pair squabbling, Saxony-Anhalt, Germany

Thomas Hinsche/ BIA / European Bee-eater (Merops apiaster) pair, Saxony-Anhalt, Germany

Tui De Roy / Volcan Alcedo Giant Tortoise (Chelonoidis nigra vandenburghi) pair in volcanic landscape, Alcedo Volcano, Isabela Island, Galapagos Islands, Ecuador

Tui De Roy / Blue-footed Booby (Sula nebouxii) males courting female, Punta Vicente Roca, Isabela Island, Galapagos Islands, Ecuador

Ingo Arndt / Baya weaver (Ploceus philippinus) subadult birds practising building 'play nest', Singapore.

Brais Seara Fernandez/ BIA / Atlantic Puffin (Fratercula arctica) pair preening, Farne Islands, United Kingdom

Richard Du Toit / Burchell's Zebra (Equus burchellii) pair nuzzling, Rietvlei Nature Reserve, South Africa

Bence Mate / Great egrets (Ardea alba) in breeding colours one with dark beak, facing each other with beaks raised towards the sky, Lake Csaj, Pusztaszer, Hungary, February.