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