David Pattyn / Bewick's swans (Cygnus bewickii) four in flight, Den Bosch, The Netherlands, January

Paul Hobson / Bewick's swan (Cygnus columbianus bewickii) flying across a full moon, UK, February 2011

David Kjaer / Small flock of Bewick's / Tundra swans (Cygnus columbianus) on water, in snow covered landscape, Gloucestershire, England

Steve Knell / Two Bewick's swans (Cygnus columbianus bewickii) in flight, Slimbridge WWT, Gloucestershire, England, January

Steve Knell / Bewick's swan (Cygnus columbianus bewickii) alert on water, Slimbridge WWT, Gloucestershire, England, January

David Tipling / Bewick's swans on water {Cygnus bewickii} WWT Slimbridge, Gloucestershire

David Kjaer / Bewick swan {Cygnus columbianus columbianus} in flight. UK.

David Kjaer / Two Bewick swans {Cygnus columbianus bewickii} flying with full-moon in sky. UK.

Rolf Nussbaumer / Bronzed cowbird {Molothrus aeneus} chick in nest of Bewick's wren, Texas, USA

Rolf Nussbaumer / Bewick's wren with nest material {Thryomanes bewickii} Texas, USA

David Kjaer / Bewick's swans, silhouette of four flying after sunset {Cygnus bewickii} UK

David Kjaer / Two Bewick's swans in flight {Cygnus bewickii} UK

David Tipling / Bewick's swan {Cygnus bewickii} on water. Slimbridge, UK. Winter Gloucestershire

Chris Packham / Bewicks swans in winter. (Cygnus columbianus bewickii) England Hampshire, UK

WILLIAM OSBORN / Bewicks swan standing on ice portrait (Cygnus columbianus bewickii) UK

Geoff Simpson / Bewick swan on water {Cygnus columbianus bewickii} Washington WWT, Co Durham, UK

Nick Upton / Bewick's swan (Cygnus columbiana bewickii) flapping its wings as it stands on a frozen marshland pool, Gloucestershire, UK, February.

Nick Upton / Bewick's swan (Cygnus columbiana bewickii) sliding on ice as it lands on a frozen marshland pool with other swans and Canada geese (Branta canadensis) in the background, Gloucestershire, UK, Febru...

Nick Upton / Bewick's swan (Cygnus columbiana bewickii) sliding on ice after landing on a frozen marshland pool, Gloucestershire, UK, February.

Nick Upton / Bewick's swan (Cygnus columbianus bewickii) in flight overhead, Gloucestershire, UK, February.

Nick Upton / Bewick's swan (Cygnus columbianus bewicki) preening as it stands in a freshwater lake, Gloucestershire, UK, February.

Nick Upton / Bewick's swan (Cygnus columbianus bewicki) calling as it bathes on a freshwater lake, Gloucestershire, UK, February.

Nick Upton / Bewick's swan (Cygnus columbianus) adult pair with one wearing a GPS logging neck collar for satellite tracking of migratory movements, WWT Slimbridge, Gloucestershire, UK, February.

David Kjaer / Bewick's swan (Cygnus columbianus) in flight with rainbow, Gloucestershire, England, UK, February.

David Kjaer / Bewick's swan (Cygnus columbianus) in flight with rainbow, Gloucestershire, England, UK, February.

Nick Upton / Tufted ducks (Aythya fuligula) and a Coot (Fulica atra) diving to forage in a shallow lake, before a Bewick's swan (Cygnus bewickii) swims in to feed, Gloucestershire, England, UK, December.

Nick Upton / Bewick's swan (Cygnus bewickii) dabbling in a lake, with a Coot (Fulica atra) swimming nearby, Gloucestershire, England, UK, December.

Nick Upton / Bewick's swan (Cygnus bewickii) dabbling in a lake near two Shelduck (Tadorna tadorna) and some diving Tufted ducks (Aythya fuligula), Gloucestershire, England, UK, December.

Nick Upton / Large mixed flock of Wigeon (Anas penelope) and Lapwings (Vanellus vanellus) taking off and in flight, over partially flooded pastureland, with alert BewickÕs swans (Anser columbianus bewickii) in the...

Nick Upton / Panning shot of Lapwings (Vanellus vanellus) taking off from partly flooded pastureland past swimming Pochard (Aythya ferina) and BewickÕs swans (Cygnus columbianus bewickii), Gloucestershire, England...

Nick Upton / Lapwings (Vanellus vanellus) landing on partly flooded pasture, with BewicksÕs swans (Cygnus columbianus bewickii) in the background, Gloucestershire, England UK, January.

Nick Upton / A group of Greylag geese (Anser anser) walking past a mixed flock of swimming Wigeon (Anas penelope), resting Shelduck (Tadorna tadorna) and BewickÕs swans (Cygnus columbianus bewickii), Gloucestershi...

Nick Upton / A pair of Common cranes (Grus grus) 'Monty' and 'Chris' reintroduced by the Great Crane Project walking on a flooded pasture past resting BewickÕs swans (Cygnus columbianus), Wigeon (Anas penelope) an...

Nick Upton / Canada geese (Branta canadensis) grazing on flooded pasture in heavy rain, with Wigeon (Anas Penelope), Lapwings (Vanellus vanellus) and BewickÕs swans (Cygnus columbianus bewickii) foraging in the ba...

Nick Upton / Bewick's swan (Cygnus columbianus bewickii) standing on flooded pastureland, surrounded by grazing Wigeon (Anas Penelope) and Lapwings (Vanellus vanellus), Gloucestershire, England, UK, February.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) group of four on water, Champagne, France, November.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) two in flight, Champagne, France, November.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) profile, Cygnes de Bewick, Champagne, France, November.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) two feeding, Champagne, France, November.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) group of three in flight, Champagne, France, December.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) group on water, Champagne, France, November.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) in flight, Champagne, France, November.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) in flight, Champagne, France, November.

Fabrice Cahez / Tundra swans (Cygnus columbianus) in flight, Champagne, France, November.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) group on water, Champagne, France, November.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) group on water, Champagne, France, November.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) group on water, Champagne, France, November.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) group in water, Champagne, France, December.

Fabrice Cahez / Bewicks swan (Cygnus columbianus bewickii) Champagne, France, December.

Rolf Nussbaumer / Bewick's wren (Thryomanes bewickii), adult perched on icy branch of Christmas cholla (Cylindropuntia leptocaulis), Hill Country, Texas, USA. January

Rolf Nussbaumer / Bewick's wren (Thryomanes bewickii), adult perched on icy branch of Possum Haw Holly (Ilex decidua) with berries, Hill Country, Texas, USA. February

Mark Carwardine / Bewick's swan (Cygnus columbianus) head portrait, Slimbridge, Gloucestershire, UK January

Mark Carwardine / Bewick's swan (Cygnus columbianus) head portrait, Slimbridge, Gloucestershire, UK, January

Mark Carwardine / Bewick's swan (Cygnus columbianus) swimming profile, Slimbridge, Gloucestershire, UK, January

David Kjaer / Bewick's swan (Cygnus columbianus) two in flight, Gloucestershire, UK January

David Kjaer / Bewick's swan (Cygnus columbianus) in flight, Gloucestershire, UK February

David Kjaer / Bewick's swans (Cygnus columbianus) two in flight, Gloucestershire, UK February

David Kjaer / Bewick's swans (Cygnus columbianus) small flock in flight, Gloucestershire, UK February

David Kjaer / Bewick's swans (Cygnus columbianus) three in flight, Gloucestershire, UK February

David Kjaer / Bewick's swan (Cygnus columbianus) in flight, Gloucestershire, UK February

Staffan Widstrand / Wild Wonders of China / Bewick's or Tundra swan (Cygnus columbianus), wintering at the Poyang Ho Lake, Jiangxi province, China

Staffan Widstrand / Wild Wonders of China / Bewick's or Tundra swan (Cygnus columbianus) and a Ruddy shelduck (Tadorna ferruginea), wintering at the Poyang Ho Lake, Jiangxi province, China

Alan Murphy / Bewick's Wren (Thryomanes bewickii), Texas

David Kjaer / Bewick's swan (Cygnus columbianus) flying, Gloucestershire, UK, December.

David Kjaer / Bewick's swan (Cygnus columbianus) group flying, Gloucestershire, UK, December.

Andy Rouse / Bewick's dwan (Cygnus columbianus) flying in at sunset, Slimbridge Wildfowl and Wetland Trust, Gloucestershire, UK, December.

Nick Upton / Bewick's swans (Cygnus bewickii) displaying and calling on flooded pastureland, Gloucestershire, UK, January.

Nick Upton / Bewick's swan (Cygnus bewickii) in flight, Gloucestershire, UK, February.

Markus Varesvuo / Three Bewick's swans (Cygnus columbianus bewickii) in flight, Estonia, April

Markus Varesvuo / Flock of adult Bewick/Tundra swans (Cycnus columbianus bewickii) in shallow water. Estonia, Baltic. April.

Nick Upton / Lapwings (Vanellus vanellus) and Golden plover (Pluvialis apricaria ) fly over Canada geese (Branta canadensis) Pochard (Aythya ferina), Tufted ducks (Aythya fuligula) and Bewick's swans (Anser bewick...

David Tipling / Common Cuckoo (Cuculus canorus) wood engraving by Thomas Bewick published in History of Land Birds Vol 1, 1797.

Robert Royse / Bewick's Wren (Thryomanes bewickii), California

Alan Murphy / Bewick's Wren (Thryomanes bewickii) singing, Texas

Alan Murphy / Bewick's Wren (Thryomanes bewickii), Texas

Alan Murphy / Bewick's Wren (Thryomanes bewickii) singing, Texas

Bence Mate / Bewick's swan {Cygnus bewickii} Hyde park, London, UK

David Welling / Bewick's wren (Thryomanes bewickii) perched on a twig in Kern County, California, United States, March

David Welling / Bewick's wren (Thryomanes bewickii) perched on a twig in Kern county, California, United states

Marie Read / Bewick's Wren (Thryomanes bewickii) portrait. Mono Lake Basin, California, USA, April.

Marie Read / Bewick's Wren (Thryomanes bewickii) portrait. Mono Lake Basin, California, USA, April.

Marie Read / Bewick's Wren (Thryomanes bewickii) perched with cocked tail. Mono Lake Basin, California, USA, April.

David Kjaer / White-fronted Goose (Anser albifrons) and a Bewick's Swan (Cygnus columbianus) on water. Gloucestershire, UK, March.

David Kjaer / Bewick's Swan (Cygnus columbianus) fighting on water. Gloucestershire, UK, March.

David Kjaer / Bewick's Swan or Tundra Swan (Cygnus columbianus) fighting by water. Gloucestershire, UK, March.

David Kjaer / Bewick's Swan or Tundra Swan (Cygnus columbianus) fighting by water. Gloucestershire, UK, March.

David Kjaer / Four Bewick's Swan / Tundra Swan (Cygnus columbianus) in flight. Gloucestershire, UK, January.

David Kjaer / Bewick's Swan or Tundra Swan (Cygnus columbianus) fighting on water. Gloucestershire, UK, March.

David Kjaer / Bewick's Swan (Cygnus columbianus) in flight. Gloucestershire, England, January.

David Kjaer / Bewick's Swan or Tundra Swan (Cygnus columbianus) foraging in water. Gloucestershire, UK, March.

David Kjaer / Bewick's Swan (Cygnus columbianus) in flight, one wearing radio transmitter around neck. Gloucestershire, England, January.

Ernie Janes / Flock of Bewick swans (Cygnus columbianus) feeding at dusk in winter, Cambridgeshire, UK,

Nature Production / Two Bewick's Swans (Cygnus columbianus bewickii) sleeping with head tucked under wing, Niigata, Japan, January

Bryan and Cherry Alexander / Nenets girl posing with pet Bewick's swan cygnet (Cygnus columbianus bewicki) at summer camp near Nadym, Yamal, Western Siberia, Russia, 2000.

Bryan and Cherry Alexander / Nenets girl playing with pet Bewick's swan cygnet (Cygnus columbianus bewicki) at summer camp near Nadym. Yamal, Western Siberia, Russia, 2000.

Bryan and Cherry Alexander / Nenets children feeding a pet young Tundra / Bewick's swan (Cygnus columbianus bewicki) at a summer camp near Nadym. Yamal, Western Siberia, Russia, 2000.