Marie Read / American avocets (Recurvirostra americana) two during aggressive (territorial) encounter, Bear River Migratory Bird Refuge, Utah, USA, May.

Alan Murphy/ BIA / Baltimore Oriole (Icterus galbula) males fighting, Texas

Alan Murphy/ BIA / Baltimore Oriole (Icterus galbula) males fighting, Texas

Thomas Marent / Boulenger's Green Anole (Anolis chloris) male displaying, Tatama National Park, Colombia

Winfried Wisniewski / Hippopotamus (Hippopotamus amphibius) in territorial display, Mkhuze Game Reserve, KwaZulu-Natal, South Africa

Sean Crane / Northern Elephant Seal (Mirounga angustirostris) male calling in territoral display with breath visible, San Simeon, California

Alan Murphy / Clay-colored Thrush (Turdus grayi) and Great Kiskadee (Pitangus sulphuratus) pair fighting, Texas

Thomas Hinsche / Ring-necked Pheasant (Phasianus colchicus) male in terriorial display, Texel, Netherlands

Suzi Eszterhas / Hyacinth Macaw (Anodorhynchus hyacinthinus) pair fighting, Pantanal, Brazil.Sequence 3 of 4

Mark Raycroft / Elk (Cervus elaphus) bull approaching car and tourist in territorial display, North America, sequence 2 of 3

Vincent Grafhorst / Hippopotamus (Hippopotamus amphibius) bull marking territory by flicking dung, Chobe National Park, Botswana

Vincent Grafhorst / Hippopotamus (Hippopotamus amphibius) bull charging in territorial display, Botswana