Nick Hawkins / Chum salmon (Oncorhynchus keta) migrate up a small river near Bella Bella, British Columbia, Canada. September

Sandesh Kadur / Slow motion clip of Amur falcons (Falco amurensis) congregating at roost site during their migration from Siberia to Africa, near Doyang reservoir, Nagaland, India, October.

Sandesh Kadur / Amur falcons (Falco amurensis) congregating during their migration from Siberia to Africa, near Doyang reservoir, Nagaland, India, October.

Sandesh Kadur / Amur falcons (Falco amurensis) congregating during their migration from Siberia to Africa, near Doyang reservoir, Nagaland, India, October.

Stefan Christmann / Emperor penguin (Aptenodytes forsteri) group walking infront of iceberg, Atka Bay, Queen Maud Land, Antarctica. October.

Nick Upton / European eel (Anguilla anguilla) elver migrating upstream, using an eel pass on the side of a weir, Somerset Levels, England, UK, July.

Dave Bevan / Male Blackbird (Turdus merula) catching European eel (Anguilla anguilla) elvers as they migrate up a waterfall, Ceredigion, Wales, UK, July.

Dave Bevan / Male Blackbird (Turdus merula) catching European eel (Anguilla anguilla) elvers as they migrate up a waterfall, Ceredigion, Wales, UK, July.

Dave Bevan / European eel (Anguilla anguilla) elvers migrating up a wet rock next to a waterfall, Ceredigion, Wales, UK, July.

Sandesh Kadur / Blue wildebeest (Connochaetes taurinus) crossing a river, Serengeti National Park, Tanzania.

David Allemand / Two Snow geese (Anser caerulescens) during migration, with dark clouds against the sun, Quebec, Canada, October.

Nick Hawkins / Atlantic salmon (Salmo salar) migrating for spawning in river, Gaspe Peninsula, Quebec, Canada, October.

Nick Hawkins / Two Atlantic salmon (Salmo salar) silhouetted against sky, Gaspe Peninsula, Quebec, Canada, October.

Ingo Arndt / Christmas Island Red Crab (Gecarcoidea natalis) blurred view of vast number of individuals moving along their annual migration route, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) crossing closed road, during annual migration, Christmas Island, Indian Ocean, Australian Territory, November 2009.

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) crossing road in huge numbers during annual migration, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) arriving in huge numbers, at coast for spawning, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) gatthered together on beach the day before spawning, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) massing on coastal rocks, the morning after spawning, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Christmas Island Red Crabs (Gecarcoidea natalis) shortly before sunrise sitting on rock ready for spawning, Christmas Island, Indian Ocean, Australian Territory

Ingo Arndt / Aerial view of Wildebeest (Connochaetes taurinus) herd migrating, Masai Mara National Reserve, Kenya, Africa

Ingo Arndt / Wildebeest (Connochaetes taurinus) herd running, Masai Mara National Reserve, Kenya

Jack Dykinga / Snow geese (Chen caerulescens) large flock with some landing, Bosque del Apache, New Mexico, USA, December.

Yashpal Rathore / Demoiselle crane (Anthropoides virgo) low angle fisheye perspective of feeding cranes. Khichan, Western Rajasthan, India. February, 2015

Yashpal Rathore / Demoiselle crane (Anthropoides virgo) resting on sand dunes during winter migration, Khichan, Western Rajasthan, India. March.

Yashpal Rathore / Demoiselle crane (Anthropoides virgo) low angle view of birds flying and landing near the chugga ghar (bird feeding enclosure ) in Khichan Village, durin their annual migration. Western Rajasthan, Ind...

Yashpal Rathore / Demoiselle cranes (Anthropoides virgo) silhouetted at dusk on a wall during their winter migration.Khichan, Western Rajasthan, India. February.

Yashpal Rathore / Demoiselle cranes (Anthropoides virgo) flying at sunrise during migration. Khichan, Western Rajasthan, India. December.

Yashpal Rathore / Demoiselle crane (Anthropoides virgo) pair flying at sunrise during winter migration. Western Rajasthan, India. December.

Yashpal Rathore / Low angle view of Demoiselle crane (Anthropoides virgo) flying and feeding during winter migration. Khichan, Western Rajasthan, India. December.

Floris van Breugel / Monarch butterflies (Danaus plexippus) over winter on Eucalyptus and Monterey Cypress trees near Pismo Beach, San Luis, California, USA December.. When temperatures warm up enough, they will embark on...

Ann & Steve Toon / Atlantic salmon (Salmo salar) leaping on upstream migration, River Tyne, Hexham, Northumberland, UK, November

Sergey Gorshkov / Siberian Tundra Reindeer (Rangifer tarandus sibiricus) herd migrating through snow, Putoransky State Nature Reserve, Putorana Plateau, Siberia, Russia

Yva Momatiuk & John Eastcott / Sockeye Salmon (Oncorhynchus nerka) group migrating upstream, Adams River, Roderick Haig-Brown Provincial Park, British Columbia, Canada

Ingo Arndt / Sockeye Salmon (Oncorhynchus nerka) group swimming upstream during spawning run, Adams River, Roderick Haig-Brown Provincial Park, British Columbia, Canada

Anup Shah / Eastern White-bearded Wildebeest (Connochaetes taurinus) herd crossing the Mara River. Masai Mara National Reserve, Kenya.

Anup Shah / Eastern White-bearded Wildebeest (Connochaetes taurinus) herd crossing the Mara River. Masai Mara National Reserve, Kenya.

Will Watson / Atlantic salmon (Salmo salar) leaping a weir, Shrewsbury, River Severn, Shropshire, England, UK. November.

Wim van den Heever / Blue wildebeest (Connochaetes taurinus) herd during migration, Masai Mara, Kenya.

Anup Shah / Blue Wildebeest (Connochaetes taurinus) herd crossing Mara River, Masai Mara, Kenya

Gerrit Vyn / Greater snow geese (Chen caerulescens) taking flight at sunset during migration. Montezuma National Wildlife Rescue, New York, USA. March.

Gerrit Vyn / Pronghorns (Antilocapra americana) crawling under fence in snow during migration, Sublette County, Wyoming, USA. March.

Theo Allofs / Blue Wildebeest (Connochaetes taurinus) herd migrating through savanna, Masai Mara, Kenya

Arne Hodalic / Nenet herdsman with Reindeer (Rangifer tarandus) during summer migration, Yamal Peninsula, Russia. May.

Alex Hyde / Red Deer herd (Cervus elaphus) moving over mountain ridge in heavy snow. Cairngorms National Park, Scotland. January. Highly Commended in the Habitat category of the British Wildlife Photography Award...

Yva Momatiuk & John Eastcott / Sockeye Salmon (Oncorhynchus nerka) migrating upstream, Adams River, Roderick Haig-Brown Provincial Park, British Columbia, Canada

Anup Shah / Eastern White-bearded Wildebeest (Connochaetes taurinus) herd crossing the Mara River. Maasai Mara National Reserve, Kenya.

Anup Shah / Eastern White-bearded Wildebeest (Connochaetes taurinus) herd crossing the Mara River. Maasai Mara National Reserve, Kenya.

Anup Shah / Common or plains zebra (Equus quagga burchelli) and Eastern White-bearded Wildebeest (Connochaetes taurinus) mixed herd crossing the Mara River. Maasai Mara National Reserve, Kenya.

Anup Shah / Eastern White-bearded Wildebeest (Connochaetes taurinus) herd crossing the Mara River. Maasai Mara National Reserve, Kenya.

Anup Shah / Common or plains zebra (Equus quagga burchelli) and Eastern White-bearded Wildebeest (Connochaetes taurinus) mixed herd crossing the Mara River. Maasai Mara National Reserve, Kenya.

Anup Shah / Burchell's Zebra (Equus burchellii) and Blue Wildebeest (Connochaetes taurinus) herd crossing river, Mara River, Masai Mara, Kenya

Denis-Huot / Wildebeest (Connochaetes taurinus) herd below stormy sky during migration, Masai-Mara game reserve, Kenya.

Denis-Huot / Rear view of Wildebeest (Connochaetes taurinus) herd crossing the Mara river, Masai-Mara game reserve, Kenya.

Markus Varesvuo / Swallow (Hirundo rustica) flying low over water, Israel, March

Markus Varesvuo / Bohemian waxwing (Bombycilla garrulus) migrating flock in flight over coast, Hanko, Finland, November 2008

Markus Varesvuo / Black stork (Ciconia nigra) in flight, Tarifa, Spain, September

Markus Varesvuo / Black kite (Milvus migrans) flying near to wind turbine, Tarifa, Spain, September 2008

Markus Varesvuo / Black stork (Ciconia nigra) in flight, Tarifa, Spain, September

Markus Varesvuo / Black stork (Ciconia nigra) in flight, Tarifa, Spain, September

Markus Varesvuo / Black Stork (Ciconia nigra) in flight on migration, Tarifa, Spain, September

Markus Varesvuo / Black stork (Ciconia nigra) in flight, Tarifa, Spain, September, digitally enhanced

Ammonite / Large group of Black wildebeest (Connochaetes gnou) migrating across savanna in a line, footage taken at night using thermal camera technology, Masai Mara, Kenya.

Anup Shah / Eastern white-bearded wildebeest (Connochaetes taurinus) herd running. Masai Mara National Reserve, Kenya. Taken with remote wide angle camera.

Anup Shah / Common or Plains zebra herd crossing the Mara River - wide angle perspective (Equus quagga burchellii). Masai Mara National Reserve, Kenya. Taken with remote wide angle camera.

Anup Shah / Eastern white-bearded wildebeest (Connochaetes taurinus) herd crossing the Mara River watched by tourists. Masai Mara National Reserve, Kenya. Taken with remote wide angle camera.

Anup Shah / Eastern white-bearded wildebeest (Connochaetes taurinus) herd running. Masai Mara National Reserve, Kenya. Taken with remote wide angle camera.

Anup Shah / Eastern white-bearded wildebeest (Connochaetes taurinus) herd running. Masai Mara National Reserve, Kenya. Taken with remote wide angle camera.

Anup Shah / Topi (Damaliscus lunatus jimela) running. Masai Mara National Reserve, Kenya. Taken with remote wide angle camera.

Anup Shah / Common or plains zebra (Equus quagga burchelli) and Eastern white-bearded wildebeest (Connochaetes taurinus) mixed herd running. Masai Mara National Reserve, Kenya. Taken with remote wide angle camera...

Anup Shah / Eastern white-bearded wildebeest (Connochaetes taurinus) herd running. Masai Mara National Reserve, Kenya. Taken with remote wide angle camera.

Anup Shah / Eastern white-bearded wildebeest (Connochaetes taurinus) herd running. Masai Mara National Reserve, Kenya. Taken with remote wide angle camera.

Anup Shah / Eastern white-bearded wildebeest (Connochaetes taurinus) herd running. Masai Mara National Reserve, Kenya. Taken with remote wide angle camera.

Anup Shah / Eastern white-bearded wildebeest (Connochaetes taurinus) herd running. Masai Mara National Reserve, Kenya. Taken with remote wide angle camera.

Graham Eaton / Salmon / Trout fish (Salmo sp) jumping a waterfall on the Afon Lledr, Betws Y Coed, Wales, October

Markus Varesvuo / Guillemots (Uria aalge) in flight in snow, Vardo, Norway, March. Winner of 2nd Prize in the Nature (Single images) category of the World Press Photo Competition 2014.

Chris & Monique Fallows / Pink Salmon (Oncorhynchus gorbuscha) migrating in small shallow river, Prince William Sound, Alaska, USA.

Alex Mustard,Alex Mustard / A female (in front) and male Sockeye salmon (Oncorhynchus nerka) over eggs in their spawning river. Adams River, British Columbia, Canada, October.

Alex Mustard / A split level photo of group of Sockeye salmon (Oncorhynchus nerka) fighting their way upstream as they migrate back to the river of their birth to spawn, trees showing autumnal colours. Adams River,...

Jack Dykinga / Sandhill crane (Grus canadensis) landing in icy pond filled with snow geese (Chen caerulescens) Bosque del Apache, New Mexico. January 2013

Cyril Ruoso / Barn Swallow (Hirundo rustica) migratory flock of forty birds perching on telephone wire, Poitou, France

Cyril Ruoso / Barn Swallow (Hirundo rustica) migratory flock perching on telephone wires along road, Poitou, France

Anup Shah,Anup Shah / Eastern White-bearded Wildebeest (Connochaetes taurinus) herd on the move Masai Mara National Reserve, Kenya, July

Anup Shah / Eastern White-bearded Wildebeest (Connochaetes taurinus) herd crossing the Mara River and clambering up steep bank. Masai Mara National Reserve, Kenya, July

Andy Rouse,Andy Rouse / African Elephant (Loxodonta africana) breeding herd in rainstorm during migration. Maasai Mara, Kenya, Africa, August.

Denis-Huot,Denis-Huot / Grant's zebra (Equus burchelli boehmi) in a migration herd of wildebeest (Connochaetes taurinus) Masai-Mara Game Reserve, Kenya

Denis-Huot / Grant's zebra (Equus burchelli boehmi) in a migration herd of wildebeest (Connochaetes taurinus) Masai-Mara Game Reserve, Kenya

Sven Zacek,Sven Zacek / Two bull Moose (Alces alces) sizing each other up during the annual rut, after sunset with migrating geese in flight. Western Estonia, September.

Sven Zacek,Sven Zacek / Common Cranes (Grus grus) in field with straw bales, prior to autumn migration. Estonia, August.

Denis-Huot / Wildebeest (Connochaetes taurinus) crossing the Mara river, Masai-Mara game reserve, Kenya

Denis-Huot / Wildebeest (Connochaetes taurinus) running for down steep bank of the Mara river during migration, Masai-Mara Game Reserve, Kenya

Denis-Huot / Wildebeest (Connchaetes taurinus) running down bank of the Mara River during migration, Masai Mara, Kenya

Denis-Huot / Wildebeest (Connochaetes taurinus) migration, herd crossing the Mara river, Masai-Mara game reserve, Kenya

Matthias Breiter / Sockeye Salmon (Oncorhynchus nerka) group jumping up waterfall, Brooks Falls, Katmai National Park, Alaska

David Tipling / Emperor Penguin (Aptenodytes forsteri) walking across the sea ice of Weddell Sea, near Snow Hill Island, Antarctica, November

Ann & Steve Toon / African elephants (Loxodonta africana) large family group on migration, Amboseli National Park, Kenya