Heike Odermatt / Brunnich's Guillemot (Uria lomvia) nesting colony on cliff, Alkefjellet, Hinlopen Strait, Svalbard, Norway

Ralph Pace / Olive Ridley Sea Turtle (Lepidochelys olivacea) females coming ashore to nest during arribada, Playa de Escobilla Sanctuary, Oaxaca, Mexico

Paul Souders/ Worldfoto / Lesser Flamingo (Phoenicopterus minor) flock nesting on island, Lake Natron, Tanzania

Paul Souders/ Worldfoto / Lesser Flamingo (Phoenicopterus minor) nesting colony, Lake Natron, Tanzania

Pal Hermansen / Avalanche on Gullemot (Uria aalge) nesting cliff on first day birds return to breed. Finnmark, Norway. March.

Ingo Arndt / Red wood ant (Formica rufa) carrying construction material to anthill (fir needles), Germany.

Ingo Arndt / Villagers collecting eggs from Olive ridley sea turtles (Lepidochelys olivacea) during the first two days of the arribada (mass nesting event). This is the only place in the world where it is legal to...

Ingo Arndt / Olive ridley sea turtles (Lepidochelys olivacea) females coming ashore during an arribada (mass nesting event) to lay eggs, Pacific Coast, Ostional, Costa Rica.

Ingo Arndt / Purple Heron (Ardea purpurea) pair courting and building nest in reeds, Germany

Pedro Narra / Green Turtle (Chelonia mydas) returning to sea, Bissagos Islands, Guinea Bissau. Endangered species. 3rd Place in the SOS Especes Menacees / SOS Endangered Species Portfolio category of the Terre Sau...

Bence Mate / Osprey (Pandion haliaetus) in flight with nesting material, Hungary, July. Nominated in the Telephoto category of the Terre Sauvage Nature Images Awards competition 2015.

Charlie Summers / Adelie Penguin (Pygoscelis adeliae) carrying stolen rock from another nest in rookery, Peterman Island, Antarctica, November.

Pete Oxford / American Crocodile (Crocodylus acutus) nest excavated by nesting female Green Iguana (Iguana iguana), Banco Chinchorro, Yucatan Peninsula, Mexico

Staffan Widstrand / Kittiwakes (Rissa tridactyla) nesting on wall of house, Vardo town, Varanger Peninsula, Norway, March.

Jack Dykinga / Great horned owl (Bubo virginianus) chicks nesting in saguaro cactus (Carnegiea gigantea), near Oracle, Sonoran Desert, Arizona, USA, May.

Jack Dykinga / Great horned owl (Bubo virginianus) chick nesting in Saguaro cactus (Carnegiea gigantea), Santa Catalina Mountains, Arizona, USA, May.

Espen Bergersen / Atlantic puffin (Fratercula arctica) two birds fighting at nesting ground, Hornoya bird cliff, Finnmark, Norway. March.

Ole Jorgen Liodden / Barn swallow (Hirundo rustica) in mud collecting nesting material, collecting nesting material, with golden bokeh affect in puddle, Svalbard, Norway, June.

Alan Murphy / Great Egret (Ardea alba) carrying nesting material, Texas

Hanne & Jens Eriksen / Ruppell's weaver (Ploceus galbula) male building nest, Oman, May

Denis-Huot / Village weaver bird (Ploceus cucullatus) male building a nest after the rains, Masai-Mara Game Reserve, Kenya. February.

Tui De Roy / Little blue / fairy penguin (Eudyptula minor) pair courting near nesting burrow, Neck Game Reserve, Bruny Island, Tasmania, Australia, December.

Tui De Roy / Little blue / fairy penguin (Eudyptula minor) walking on pathway to nesting burrows, Neck Game Reserve, Bruny Island, Tasmania, Australia, December.

Ben Cranke / Gentoo Penguin (Pygoscelis papua) nesting, Petermann Island, Antarctic Peninsula, Antarctica

Bert Willaert / Green-backed Firecrown (Sephanoides sephanoides) nesting next to a hiking trail in Mocha Island National Reserve, Mocha Island, Chile, December

Roland Seitre / Olive Ridley Sea Turtle (Lepidochelys olivacea) females coming ashore to lay eggs during an arribada nesting event, Ostional Beach, Costa Rica

Ingo Arndt / Olive Ridley Sea Turtle (Lepidochelys olivacea) females coming ashore to lay eggs during an arribada nesting event, Ostional Beach, Costa Rica

Mark Hamblin / 2020VISION / Barn swallow (Hirundo rustica) alighting at pond, collecting material for nest building, Scotland, UK, June. Did you know? Barn swallows will feed their nestlings up to 400 times every day.

Pete Oxford / Black-browed Albatross (Thalassarche melanophrys) nesting colony, Steeple Jason Island, Falkland Islands

Pete Oxford / Black-browed Albatross (Thalassarche melanophrys) nesting colony, Steeple Jason Island, Falkland Islands

Michael Quinton / Great Gray Owl (Strix nebulosa) parent protecting eggs in nest, North America

Michael Quinton / Great Gray Owl (Strix nebulosa) incubating eggs on nest, North America

Flip de Nooyer / Eurasian Kestrel (Falco tinnunculus) group of five juveniles in nesting box, Europe

Flip de Nooyer / Gentoo Penguin (Pygoscelis papua) two downy chicks standing together in nesting colony, Antarctica

Jim Brandenburg / Bald Eagle (Haliaeetus leucocephalus) bringing fish to mate in nest, Northwoods, Minnesota

Tui De Roy / Salvin's Albatross (Thalassarche salvini) returning en masse to crowded nesting colony at sunset, Proclamation Island, Bounty Islands, New Zealand

Tom Vezo / Piping Plover (Charadrius melodus) sitting on eggs in nest on ground, Long Island, New York

Yva Momatiuk & John Eastcott / Gila Woodpecker (Melanerpes uropygialis) nesting in Saguaro (Carnegiea gigantea) in desert, spring, Sonoran Desert National Monument, Arizona

Flip de Nooyer / Common Eider (Somateria mollissima) adult female at down nest with eggs, Europe

Gerry Ellis / Greater Flamingo (Phoenicopterus ruber) nesting colony with mud nests, Inagua National Park, Bahamas

Konrad Wothe / Kentish Plover (Charadrius alexandrinus) male at nest, Europe

Tui De Roy / Atlantic Puffin (Fratercula arctica) at entrance to nesting burrow during breeding season, Skomer Island, Wales

Michael Quinton / Red-necked Grebe (Podiceps grisegena) parent on nest with eggs in boreal pond, Alaska

Michael Quinton / Northern Hawk Owl (Surnia ulula) at nest with chicks, Alaska

Tui De Roy / Blue-footed Booby (Sula nebouxii) male incubating eggs with webbed feet, Seymour Island, Galapagos Islands, Ecuador

Tui De Roy / Red-footed Booby (Sula sula) couple courting in Croton shrub, Wenman Island, Galapagos Islands, Ecuador

Tui De Roy / Blue-footed Booby (Sula nebouxii) pair overlooking nesting colony, Punta Vicente, Isabella Island, Galapagos Islands, Ecuador

Tui De Roy / Brown Pelican (Pelecanus occidentalis) three chicks begging for food from freshly returned parent, Academy Bay, Santa Cruz Island, Galapagos Islands, Ecuador

Tui De Roy / Chinstrap Penguin (Pygoscelis antarctica) bowing over twin chicks Nelson Island, South Shetland Islands, Antarctica

Tui De Roy / Black-footed Albatross (Phoebastria nigripes) incubating single egg, Midway Atoll, Hawaii

Tui De Roy / Emperor Penguin (Aptenodytes forsteri) group tobogganing across vast distance of fast ice to nesting rookery, Kloa Point, Edward VIII Gulf, Antarctica

Tui De Roy / Adelie Penguin (Pygoscelis adeliae) nesting colony on granite outcrop, Petermann Island, Antarctica

Tui De Roy / Emperor Penguin (Aptenodytes forsteri) group, near Ekstrom Ice Shelf, Weddell Sea, Antarctica

Tui De Roy / Emperor Penguin (Aptenodytes forsteri) group, near Ekstrom Ice Shelf, Weddell Sea, Antarctica

Mitsuaki Iwago / Australian Gannet (Morus serrator) nesting colony, Australia

Mitsuaki Iwago / Australian Gannet (Morus serrator) nesting colony, Australia

Shin Yoshino / Osprey (Pandion haliaetus) carrying branch to nesting site, Earthquake Lake, Idaho

WILLIAM OSBORN / Song thrush feeds 10-day-old chicks at nest, UK

Winfried Wisniewski / White Stork (Ciconia ciconia) pair building nest, Extremadura, Spain

Winfried Wisniewski / White Stork (Ciconia ciconia) landing with nest-building material, Extremadura, Spain

Heike Odermatt / Brunnich's Guillemot (Uria lomvia) nesting colony on cliff, Alkefjellet, Hinlopen Strait, Svalbard, Norway

Heike Odermatt / Gentoo Penguin (Pygoscelis papua) nesting colony and young Southern Elephant Seal (Mirounga leonina), Falkland Islands

Donald M. Jones / American Cliff Swallow (Petrochelidon pyrrhonota) gathering mud for nest building, Montana

Donald M. Jones / American Cliff Swallow (Petrochelidon pyrrhonota) trio gathering mud for nest building, Montana

Donald M. Jones / American Robin (Turdus migratorius) with nesting material, Montana

Agustin Esmoris / Black-browed Albatross (Thalassarche melanophrys) nesting colony on coast, Falkland Islands

Agustin Esmoris / Black-browed Albatross (Thalassarche melanophrys) nesting colony, Falkland Islands

Agustin Esmoris / Blue-eyed Cormorant (Phalacrocorax atriceps) pair courting in nesting colony, Falkland Islands

Thomas Marent / Black Oropendola (Gymnostinops guatimozinus) carrying nesting material, Rio Claro Nature Reserve, Colombia

Thomas Marent / Black Oropendola (Gymnostinops guatimozinus) collecting nest material, Rio Claro Nature Reserve, Colombia

Piotr Naskrecki / Village Weaver (Ploceus cucullatus) building nest, Gorongosa National Park, Mozambique

Ashley Cooper / King penguin (Aptenodytes patagonicus) moulting from down to adult feathers at Gold harbour, South Georgia, Southern Ocean. February.

Sylvain Cordier / Northern pika (Ochotona hyperborea ) carrying plants to build nest, Yttygran Island, Far East Russia

Yva Momatiuk & John Eastcott / Northern Gannet (Morus bassanus) and Black-legged Kittiwake (Rissa tridactyla) colony, Langanes Peninsula, Iceland

Yva Momatiuk & John Eastcott / Common Murre (Uria aalge) and Black-legged Kittiwake (Rissa tridactyla) colony on cliff, Latrabjarg, Westfjords, Iceland

Tui De Roy / Flightless Cormorant (Phalacrocorax harrisi) carrying nesting material, Cape Douglas, Fernandina Island, Galapagos Islands, Ecuador

Tui De Roy / Flightless Cormorant (Phalacrocorax harrisi) pair collecting nesting material, Playa Negra, Isabela Island, Galapagos Islands, Ecuador

Tui De Roy / Flightless Cormorant (Phalacrocorax harrisi) carrying nesting material, Punta Albemarle, Isabela Island, Galapagos Islands, Ecuador

Alan Murphy/ BIA / Killdeer (Charadrius vociferus) on nest with eggs, Texas

Alfred Trunk/ BIA / European Ground Squirrel (Spermophilus citellus) carrying nesting material, Austria

Thomas Hinsche/ BIA / Eurasian Penduline-Tit (Remiz pendulinus) male building nest, Saxony-Anhalt, Germany

Graeme Guy/ BIA / Black-and-red Broadbill (Cymbirhynchus macrorhynchos) pair building nest, Sabah, Borneo, Malaysia

Matthew Studebaker/ BIA / American Cliff Swallow (Petrochelidon pyrrhonota) collecting mud for nest, Wyoming

Tui De Roy / Gentoo Penguin (Pygoscelis papua) carrying nesting material, Dunbar Island, Falkland Islands

Tui De Roy / Gentoo Penguin (Pygoscelis papua) on nest, Dunbar Island, Falkland Islands

Agustin Esmoris / Red-rumped Cacique (Cacicus haemorrhous) pair building nest, Argentina

Tui De Roy / Nazca Booby (Sula granti) pair building nest, Punta Suarez, Espanola Island, Galapagos Islands, Ecuador

Tui De Roy / Flightless Cormorant (Phalacrocorax harrisi) pair at nest with eggs, Puerto Pajas, Isabela Island, Galapagos Islands, Ecuador

Tui De Roy / Brown Pelican (Pelecanus occidentalis) on nest with eggs along coast, Santa Cruz Island, Galapagos Islands, Ecuador

Tui De Roy / Brown Pelican (Pelecanus occidentalis) on nest with eggs along coast, Santa Cruz Island, Galapagos Islands, Ecuador

Michael Quinton / Douglas's Squirrel (Tamiasciurus douglasii) collecting nesting material, Alaska

Konrad Wothe / Blue Tit (Cyanistes caeruleus) parent with begging chicks in nest box, Bavaria, Germany

Ingo Arndt / Red wood ant (Formica rufa) carrying construction material to anthill (fir needle), Germany.

Thomas Marent / Roseate Spoonbill (Platalea ajaja) carrying nesting material, Los Llanos, Colombia

Glenn Bartley/ BIA / Rockhopper Penguin (Eudyptes chrysocome) nesting colony, Falkland Islands

Nate Chappell/ BIA / African Fish Eagle (Haliaeetus vocifer) carrying nesting material, Chobe National Park, Botswana