Danny Green / Snow Geese (Chen caerulescens) in flight, silhouetted against colourful dusk sky. Bosque del Apache, New Mexico, USA, November.

Danny Green / Snow Goose (Chen caerulescens), coming in to land. Bosque del Apache, New Mexico, USA, November.

Konrad Wothe / Flock of Snow Geese (Chen caerulescens atlanticus / Chen caerulescens) in flight to their winter roosting site, crossing a full moon, Bosque del Apache, New Mexico, USA, November

Konrad Wothe / Three Snow Geese (Chen caerulescens atlanticus / Chen caerulescens) in flight, Bosque del Apache, New Mexico, USA, November

Konrad Wothe / Mixed flock of Snow geese (Chen caerulescens atlanticus / Chen caerulescens) and Sandhill cranes (Grus canadensis) at wintering area at dawn, with full moon, Bosque del Apache, New Mexico, USA, Novemb...

Chadden Hunter / Snow goose with gosling (Chen caerulescens) at sunset. Taken on location for BBC Frozen Planet series, 2008

Charlie Summers / Three Snow Geese banking and gliding in preparation for a landing (Chen caerulescens). Bosque del Apache, New Mexico, January.

Jenny E. Ross / Snow Geese (Chen caerulescens) and Ross's Geese (Chen rossii) taking off from field where they have been feeding, Imperial Valley, California, USA.

Steven Kazlowski / Thousands of Snow geese (Chen caerulescens) taking flight to begin their migration south from their summer nesting grounds in the Arctic, Alaska.

Pete Oxford / Close up of Snow Goose (Chen caerulescens) with head tucked into wing, Slimbridge Wildfowl and Wetlands Trust, SW England, UK captive

Eric Baccega / Large flock of Snow geese (Anser / Chen caerulescens) in flight, Cap Tourmente, Quebec, Canada

Andy Rouse / Large flock of Snow geese (Chen caerulescens) taking off, Bosque del Apache National Wildlife Refuge, New Mexico, USA

Andy Rouse / Aerial view of a large flock of Snow geese (Chen caerulescens) on lake, Bosque del Apache, New Mexico, USA

David Tipling / Snow geese {Anser / Chen caerulescens} flock taking off, Bosque del Apache, New Mexico, USA, January

Andy Rouse / Snow geese (Chen caerulescens) landing, Bosque del Apache, New Mexico, USA

Andy Rouse / Flock of Snow geese (Chen caerulescens) taking off, Bosque del Apache, New Mexico, USA

LYNN M. STONE / Snow Goose chick (Chen caerulescens) NE Manitoba, Canada

Mark Brownlow / Aerial view of Snow goose (Chen caerulescens) flock in flight, part of annual migration, Bombay Hook NWR, Delaware Bay, Delaware, USA. November 2005, BBC Planet Earth

Tom Vezo / Snow geese fly in V formation {Chen caerulescens} Bosque del Apache, NM, USA.

Tom Vezo / Snow geese at sunset {Chen caerulescens} Bosque del Apache, NM, USA.

Barry Mansell / Snow goose {Chen caerulescens} landing amongst flock, New Mexico, USA.

Jim Brandenburg / Snow Goose (Chen caerulescens) flock flying in formation during migration, with individuals of both color phases, California

Rolf Nussbaumer / Two Snow geese flying {Chen caerulescens} Bosque del Apache, New Mexico, USA

Rolf Nussbaumer / Snow goose in flight {Chen caerulescens} Bosque del Apache, NM, USA.

Danny Green / Snow Goose (Chen caerulescens) coming in to land. Bosque del Apache, New Mexico, USA, November.

Danny Green / Snow Goose (Chen caerulescens), coming in to land. Bosque del Apache, New Mexico, USA, November.

Danny Green / Snow Geese (Chen caerulescens) in flight, silhouetted against dawn light. Bosque del Apache, New Mexico, USA, November.

Danny Green / Flock of Snow Geese (Chen caerulescens) in flight. Bosque del Apache, New Mexico, USA, November.

Mark Carwardine / Snow goose (Anser / Chen caerulescens) flock at dawn, Bosque del Apache National Wildlife Refuge, New Mexico, USA

Mark Carwardine / Sandhill cranes (Grus canadensis) feeding with Snow geese (Anser / Chen caerulescen) flying, Bosque del Apache National Wildlife Refuge, New Mexico, USA

Mark Carwardine / Snow goose (Anser Chen caerulescens) flock flying, Bosque del Apache National Wildlife Refuge, New Mexico, USA

Mark Carwardine / Snow geese (Anser / Chen caerulescens) flock on ground feeding with some flying, Bosque del Apache National Wildlife Refuge, New Mexico, USA

Mark Carwardine / Snow geese (Anser / Chen caerulescens) flying, Bosque del Apache National Wildlife Refuge, New Mexico, USA

Mark Carwardine / Two Snow geese (Anser / Chen caerulescens) flying, Bosque del Apache National Wildlife Refuge, New Mexico, USA

Donald M. Jones / Snow Goose (Chen caerulescens) group flying, Fairfield, Montana

Donald M. Jones / Snow Goose (Chen caerulescens) flock taking flight, Fairfield, Montana

Tom Vezo / Snow Goose (Chen caerulescens) blue and regular phase flying, Bosque Del Apache National Wildlife Refuge, New Mexico

Tom Vezo / Snow Goose (Chen caerulescens) juvenile, Bosque Del Apache National Wildlife Refuge, New Mexico

Tom Vezo / Snow Goose (Chen caerulescens) blue phase, Bosque Del Apache National Wildlife Refuge, New Mexico

Tom Vezo / Snow Goose (Chen caerulescens) blue phase, Bosque Del Apache National Wildlife Refuge, New Mexico

Tom Vezo / Snow Goose (Chen caerulescens) blue phase flying, Bosque Del Apache National Wildlife Refuge, New Mexico

Tom Vezo / Snow Goose (Chen caerulescens) flock taking flight, Bosque Del Apache National Wildlife Refuge, New Mexico

Tom Vezo / Snow Goose (Chen caerulescens) flock flying in formation during migration, Bosque Del Apache National Wildlife Refuge, New Mexico

Todd Mintz / Snow goose (Chen caerulescens) flock resting during northern migration in spring, Canadian prairies, Saskatchewan, Canada, March

Todd Mintz / Snow goose (Chen caerulescens) three in flight on northern migration in spring, Canadian prairies, Saskatchewan, Canada, March

Todd Mintz / Snow goose (Chen caerulescens) flock in flight on northern migration in spring, Canadian prairies, Saskatchewan, Canada, March

Roger Powell / Lesser snow goose (Chen caerulescens) small flock in flight over water, East Chevington, Druridge Bay, Northumberland, UK. September

Roger Powell / Lesser snow goose (Chen caerulescens) small flock in flight over water, East Chevington, Druridge Bay, Northumberland, UK. September

Loic Poidevin / Snow goose (Chen caerulescens) flock migrating south, Quebec, Canada, October

Loic Poidevin / Injured Snow goose (Chen caerulescens) with part of a drinks can stuck on its beak, Quebec, Canada, October

Loic Poidevin / Snow goose (Chen caerulescens) wounded by a hunter, Victoriaville, Quebec, Canada, October

Loic Poidevin / Arrival of Snow geese (Anser / Chen caerulescens) large flock on water and in flight, Victoriaville, Canada, October

Loic Poidevin / Snow goose (Chen caerulescens) in flight, Quebec, Canada, October

Loic Poidevin / Three Snow geese (Chen caerulescens) in flight, Quebec, Canada, October

Loic Poidevin / Six Snow geese (Chen caerulescens) flying during southward migration, Quebec, Canada, October

Loic Poidevin / Juvenile Snow goose (Chen caerulescens) feeding, Quebec, Canada, October

Loic Poidevin / Snow goose (Chen caerulescens) juvenile grazing, Quebec, Canada, October

Loic Poidevin / Group of Snow geese (Chen caerulescens) adults and juveniles, Vitoriaville, Quebec, Canada, October

Loic Poidevin / Flock of Snow geese (Chen caerulescens) in flight, migrating south, Bic National Park, Quebec, Canada, October

Loic Poidevin / Snow goose (Chen caerulescens) in flight, calling, Quebec, Canada, October

Todd Mintz / Snow goose (Chen caerulescens) large flock gathered on flooded plains during migration, Saskatchewan, Canada.

Todd Mintz / Snow goose (Chen caerulescens) large flock flying during migration, Saskatchewan, Canada.

Charlie Summers / Snow Goose (Chen caerulescens) in flight, preparing to land. Bosque del Apache, New Mexico, December.

Charlie Summers / Snow Geese (Chen caerulescens) calling on water - immatures in dusky plumage. Bosque del Apache, New Mexico, December.

Konrad Wothe / Flock of Snow geese (Chen caerulescens atlanticus / Chen caerulescens) at wintering area, Bosque del Apache, New Mexico, USA, November

Konrad Wothe / Flock of Snow Geese (Chen caerulescens atlanticus / Chen caerulescens) on water at sunrise, white and grey phases, Bosque del Apache, New Mexico, USA, November

Konrad Wothe / Flock of Snow Geese (Chen caerulescens atlanticus / Chen caerulescens) in flight, abstract, Bosque del Apache, New Mexico, USA, November

Konrad Wothe / Flock of Snow Geese (Chen caerulescens atlanticus / Chen caerulescens) in flight and on ground at wintering area, Bosque del Apache, New Mexico, USA, November

Konrad Wothe / Snow Geese (Chen caerulescens atlanticus / Chen caerulescens) in flight, white and grey phase, Bosque del Apache, New Mexico, USA, November

Konrad Wothe / Flock of Snow Geese (Chen caerulescens atlanticus / Chen caerulescens) in flight and on ground at wintering area, Bosque del Apache, New Mexico, USA, November

Konrad Wothe / Large flock of Snow geese (Chen caerulescens atlanticus / Chen caerulescens) on water at sunrise with flock of waterfowl flying overhead, Bosque del Apache, New Mexico, USA, November

Chadden Hunter / Snow geese (Chen caerulescens) standing on ice, Arctic. Taken on location for BBC Frozen Planet series, 2008

Chadden Hunter / Snow goose egg hatching (Chen caerulescens) taken on location for BBC Frozen Planet series, 2008

Chadden Hunter / Snow geese goslings (Chen caerulescens) taken on location for BBC Frozen Planet series, 2008

Loic Poidevin / Two Snow Geese (Chen / Anser caerulenscens) in flight. Breton Marsh, French Atlantic Coast, March.

Steve Gettle / Snow Goose (Chen caerulescens) flying, Bosque del Apache National Wildlife Refuge, New Mexico

Steve Gettle / Snow Goose (Chen caerulescens) flying, Bosque del Apache National Wildlife Refuge, New Mexico

Steve Gettle / Snow Goose (Chen caerulescens) flying, Bosque del Apache National Wildlife Refuge, New Mexico

Steven Kazlowski / Snow goose (Chen caerulescens) eggs in a down feather nest along Kasegaluk lagoon, outside the arctic village of Point Lay, Alaska, USA, June

Steven Kazlowski / Snow goose (Chen caerulescens) eggs in a down feather nest along Kasegaluk lagoon, outside the arctic village of Point Lay, Alaska, USA, June

Charlie Summers / Snow Goose / Blue Goose (Anser / Chen caerulescens) flying. Bosque del Apache National Wildlife Refuge, New Mexico, USA.

B&S Draker / Snow Goose (Chen caerulescens) flock on water at sunrise. Bosque del Apache National Wildlife Refuge, New Mexico, USA, January.

Matthias Breiter / Snow Goose (Chen caerulescens) flock flying above Skagit River flats, Washington

Matthias Breiter / Snow Goose (Chen caerulescens) flock on Skagit River flats, Washington

Matthias Breiter / Snow Goose (Chen caerulescens) flock flying above Skagit River flats, Washington

Matthias Breiter / Snow Goose (Chen caerulescens) flocks flying above Skagit River flats, Washington

Sebastian Kennerknecht / Snow Goose (Chen caerulescens) flock taking flight with Sandhill Cranes (Grus canadensis) below, Bosque del Apache National Wildlife Refuge, New Mexico

Sebastian Kennerknecht / Snow Goose (Chen caerulescens) flying, Bosque del Apache National Wildlife Refuge, New Mexico

Sebastian Kennerknecht / Snow Goose (Chen caerulescens) flock flying at sunrise, Bosque del Apache National Wildlife Refuge, New Mexico

Eric Baccega / Snow Geese (Chen caerulescens) in flight. Quebec, Canada, January.

Eric Baccega / Snow Geese (Chen caerulescens) in flight. Quebec, Canada, January.

Eric Baccega / Snow Geese (Chen caerulescens) in flight. Quebec, Canada, January.

Eric Baccega / Snow Geese (Chen caerulescens) in flight. Quebec, Canada, January.

Eric Baccega / Large flock of Snow Geese (Chen caerulescens) in flight. Quebec, Canada, January.

Eric Baccega / Large flock of Snow Geese (Chen caerulescens) in flight. Quebec, Canada, January.

Jeff Vanuga / A flock of Snow Geese (Chen caerulescens) taking flight. Mississippi flyway migration route, USA, December.