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.