Martin Dohrn / Hippo (Hippopotamus amphibius) in threat pose, Masai Mara, Kenya. Image taken at night using thermal camera technology without artificial lighting.

Edwin Giesbers / Arctic tern (Sterna paradisaea) in flight, vocalising, aggresive behaviour, Farne Islands, Northumberland, UK, June

Nick Garbutt / Male Panther Chameleon (Furcifer pardalis) in aggresive posture, displaying at its own reflection in a mirror. Masoala National Park, north east Madagascar.

Tony Heald / Lappet faced vulture {Torgos tracheliotus} being attacked by an aggresive Black backed jackal {Canis mesomelas} Etosha NP, Namibia

Ashley Cooper / Lesser black backed gull (Larus fuscus) nesting on Walney Island off Barrow in Furness, England, UK, June.

Sergey Gorshkov / Snow geese (Chen caerulescens caerulescens) aggresive male biting neck of another male mating with female, Wrangel Island, Far Eastern Russia, June.

Sergey Gorshkov / Snow geese (Chen caerulescens caerulescens) aggresive male biting neck of another male mating with female, Wrangel Island, Far Eastern Russia, June.

Michel Poinsignon / Arctic tern (Sterna paradisaea) in flight, vocalising, aggresive behaviour, Farne Islands, Northumberland, UK, July

Michel Poinsignon / Arctic tern (Sterna paradisaea) in flight, vocalising, aggresive behaviour, Farne Islands, Northumberland, UK, July

Michel Poinsignon / Arctic tern (Sterna paradisaea) in flight, vocalising, aggresive behaviour, Farne Islands, Northumberland, UK, July

Diane McAllister / Japanese Macaque (Macaca fuscata) aggressive adult male approaches another monkey in Jigokudani, Japan. February

Edwin Giesbers / Sumatran tiger (Panthera tigris sumatrae) walking, and baring teeth in aggresive display, captive