Southern elephant seal (Mirounga leonina) bull issuing a vocalization challenge at Gold Harbour on 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

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