Angelo Gandolfi / Two European Grey wolves (Canis lupus) one howling, in snow, captive, Bayerisch National Park, Germany

Edwin Giesbers / Two European grey wolves (Canis lupus) interacting, captive, Norway, February.

Peter Cairns / Pair of European grey wolves (Canis lupus) interacting, Tromso, Norway, captive, April

LYNN M. STONE / Grey wolf portrait, Minnesota, USA.

Peter Cairns / European wolf (Canis lupus) running through snow in birch forest, Tromso, Norway, captive, April

Florian Möllers / Wolf (Canis lupus) pack running in deep snow, captive in enclosure of the Bavarian Forest National Park, Germany, February

Tom Vezo / Grey wolf pup on log {Canis lupus} captive, Montana, USA

Edwin Giesbers / Grey wolf (Canis lupus) head portrait, snarling with teeth bared in aggressive expression, captive.

Edwin Giesbers / Two European grey wolves (Canis lupus) interacting, captive, Norway, February.

Edwin Giesbers / Grey wolf (Canis lupus) close up portrait, captive

Eric Baccega / Two European grey wolves (Canis lupus) displaying social grooming behaviour, captive. Bayerischerwald National Park, Germany.

Staffan Widstrand / Grey wolf silhouette in snow {Canis lupus} Toropets, Russia.

Staffan Widstrand / Grey wolf female head portrait, Carpathian mtns, Romania, captive.

Eric Baccega / Two European grey wolves (Canis lupus) play fighting in snow, captive. Bayerischerwald National Park, Germany.

Lassi Rautiainen / Wild Grey wolf (Canis lupus) Kuhmo, Finland, September

Edwin Giesbers / Grey wolf (Canis lupus) individuals showing submissive and aggressive behaviour, captive

Edwin Giesbers / Two European grey wolves (Canis lupus), captive, Norway, February.

Edwin Giesbers / Two European grey wolves (Canis lupus) fighting in snow, captive, Norway, February.

Mary McDonald / Grey wolf (Canis lupus). USA

Edwin Giesbers / Grey wolf (Canis lupus) head portrait, viewed through autumn colours, captive.

Shattil & Rozinski / Mexican wolf howling {Canis lupus baileyi} captive, endangered, USA

Tom Vezo / Grey wolves showing fur colour variation. (Canis lupus)

Wild Wonders of Europe / Widstr / Eurasian grey wolf (Canis lupus lupus) at a vulture watching site in the Madzharovo valley, Eastern Rhodope Mountains, Bulgaria, May 2013.

Tom Vezo / Portrait grey wolf howling

David Welling / Grey wolf snarling over carcass in snow

Wild Wonders of Europe / Widstrand / European grey wolf (Canis lupus) carrying part of a carcass, Kuhmo, Finland, July 2009 Wild Wonders kids book.

Eric Baccega / European grey wolf (Canis lupus) howling in winter, captive. Bayerischerwald National Park, Germany.

George Sanker / Grey Wolf (Canis lupus) pouncing through grass. Yellowstone National Park, Wyoming, USA, June.

Eric Baccega / Two European grey wolves (Canis lupus) howling in winter landscape, captive. Bayerischerwald National Park, Germany.

LYNN M. STONE / Grey Wolf cub at waters edge {Canis lupus} captive USA

Tom Vezo / Grey wolf pup howling {Canis lupus} captive, Montana, USA

LYNN M. STONE / Grey wolves playing in snow {Canis lupus} captive, USA.

Jeff Vanuga / Silhouette of Gray Wolf (Canis lupus) standing on a rock by the Yellowstone River. Yellowstone National Park, USA,

Tom Vezo / Grey wolf (Canis lupus) howling

Claudio Contreras / Mexican wolf (Canis lupus baileyi), Mexican subspecies, probably extinct in the wild, captive.

Staffan Widstrand / European Grey Wolf {Canislupus} hunting rodents in snow, Toropets, Russia

Tim Edwards / Grey wolf among aspen trees. USA

Wild Wonders of Europe / Widstra / European / Grey wolf (Canis lupus) at sunset, Kuhmo, Finland, July 2009. WWE INDOOR EXHIBITION

Lassi Rautiainen / Two Grey wolves (Canis lupus) in woodland wetlands, Kuhmo, Finland, July

Wild Wonders of Europe / Widstr / Wolf (Canis lupus lupus) near Deven, Western Rhodope Mountains, Bulgaria, May 2013.

George Sanker / Grey Wolf (Canis lupus) Yellowstone National Park, Wyoming, USA, May.

Bertie Gregory / Vancouver Island grey wolf (Canis lupus crassodon) subadult on the coastline, Vancouver Island, British Columbia, Canada, August.

Steven Kazlowski / Grey wolf (Canis lupus) female with a black coat in the foothills of the Takshanuk mountains, South-East Alaska, USA

Bertie Gregory / Vancouver Island Grey wolf (Canis lupus crassodon) dark morph Vancouver Island, British Columbia, Canada.

Jeff Turner / Grey wolf (arctic form) with pup near den, Ellesmere Island, Canada

George Sanker / Grey wolf (Canis lupus) walking through water, Yellowstone National Park, USA, North America, May

Roland Seitre / Polar Wolf (Canis lupus arctos), a high arctic variant of the Grey Wolf, yawning. Captive. Lobo Park, Antequera, Spain, January.

Eric Baccega / Male Arctic wolf (Canis lupus arctos) walking on pack ice, Ellesmere Island, Nunavut, Canada, June 2012

Staffan Widstrand / Portrait of Grey (Arctic) wolf {Canis lupus} in snow. Ellesmere Island, Canada.

Lynn M Stone / Grey wolves, white /arctic form running in snow {Canis lupus} captive US

Lynn M Stone / Portrait of grey wolf howling in the snow.

Jeff Turner / White arctic race grey wolf mother and pup (Canis lupus) walking near den, Ellesmere Island, Canada

Jeff Wilson / Adult Arctic wolf (Canis lupus) Ellesmere Island, Nunavut, Canada, June 2008. Taken on location for BBC series, Frozen Planet, Summer