Male black grouse (Lyrurus tetrix) fighting on snow covered field, Finland

Chinstrap penguin (Pygoscelis antarctica), ecstatic display at breeding colony at Half Moon Island, Antarctica, Polar Regions

Adult bull southern elephant seal (Mirounga leonina) issuing a bellow towards another male, Gold Harbour, South Georgia, Polar Regions

Eider duck (Somateria mollissima), male and female. Eider male and female interacting with each other in a winter raft. Demonstration of size difference between male and female.

Pheasant (Phasianus colchicus), mating male, flapping wings, calling, Blankenfelde, Germany, Europe

African penguin (Spheniscus demersus), adult, on land, calling, mating, Betty's Bay, Stony Point Nature Reserve, Western Cape, South Africa, Africa

Bull elk (Cervus canadensis) with misty breath in winter, Denver, Colorado, United States of America

Bull elk (Cervus canadensis) bugling in a field, Denver, Colorado, United States of America

Bull elk (Cervus canadensis) bugling, Denver, Colorado, United States of America