Yukihiro Fukuda / Male Japanese giant salamander (Andrias japonicus) protecting its nest from another intruding male, Hino River, Tottori-ken, Japan, September.

Julian Hume / Illustration of extinct birds, Pair of Rodrigues solitaires (Pezophaps solitaria) (Ex.1762) chase an intruding male from their territory. Leguat's rails (Erythromachus leguati) (bottom left) (Ex.1762)...

Roger Powell / Male Stone chat (Saxicola rubicola) aggressively flicking its tail at an intruding male. Guerreiro, Castro Verde, Alentejo, Portugal, May.

Roger Powell / Male Stone chat (Saxicola rubicola) aggressively flicking its tail at an intruding male. Guerreiro, Castro Verde, Alentejo, Portugal, May.

Roger Powell / Male Stone chat (Saxicola rubicola) aggressively flicking its tail at an intruding male. Guerreiro, Castro Verde, Alentejo, Portugal, May.

Roger Powell / Male Stone chat (Saxicola rubicola) aggressively flicking its tail at an intruding male. Guerreiro, Castro Verde, Alentejo, Portugal, May.

Sumio Harada / Red Fox (Vulpes vulpes) fighting with an intruding American Badger (Taxidea taxus) at entrance to burrow, Yellowstone National Park, Montana. Sequence 2 of 3, Yellowstone National Park, Montana

Sergey Gorshkov / Long-tailed Jaeger (Stercorarius longicaudus) flying over intruding Arctic Fox (Alopex lagopus) near its nest, Wrangel Island, Russia

Cyril Ruoso / Chacma Baboon (Papio ursinus) in car, South Africa

Cyril Ruoso / Chacma Baboon (Papio ursinus) group playing with curtains from building, South Africa

Paul Williams / Giant otter (Pteronura brasiliensis) intimidates Yacare caiman (Caiman yacare) who is intruding on the otters territory, specifically latrine, Pantanal, Pocone, Brazil

Mark Moffett / Amazon Ant (Polyergus sp) female worker positioning mandibles to pierce the head of an ant from an alien nest, Sagehen Creek, California