ZSSD / Pygmy Hippopotamus (Hexaprotodon liberiensis) portrait, endangered, native to West Africa

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) pair near fish trap

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) summer, Chobe River, Chobe National Park, Botswana

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) backside, summer, Chobe River, Chobe National Park, Botswana

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) charging, Khwai River, Botswana

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) bull threat yawning, Khwai River, Botswana

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) group, Chobe River, Botswana

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) two bulls fighting, Moremi Wildlife Reserve, Botswana

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) threat yawning, Moremi Wildlife Reserve, Botswana

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) toes coming out of the water as he is rolling, Moremi Wildlife Reserve, Botswana

Gerry Ellis / Hippopotamus (Hippopotamus amphibius) male displaying, Linyanti Swamp, Botswana

Mitsuaki Iwago / Hippopotamus (Hippopotamus amphibius) standing in water, Serengeti National Park, Tanzania

Shin Yoshino / Hippopotamus (Hippopotamus amphibius) pair fighting in water, Masai Mara National Reserve, Kenya

Shin Yoshino / Hippopotamus (Hippopotamus amphibius) group in water, Masai Mara National Reserve, Kenya

Shin Yoshino / Hippopotamus (Hippopotamus amphibius) pair fighting in water, Masai Mara National Reserve, Kenya

Suzi Eszterhas / Hippopotamus (Hippopotamus amphibius) mother with young calf showing aggressive behavior toward other hippo, Masai Mara National Reserve, Kenya

Suzi Eszterhas / Hippopotamus (Hippopotamus amphibius) two week old baby resting atop it's mothers back along the river bank, Masai Mara National Reserve, Kenya

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) pod, Maputaland, South Africa

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) pod resting, Okavango Delta, Botswana

Patricio Robles Gil / Pygmy Hippopotamus (Hexaprotodon liberiensis) grazing in grassland, Ivory Coast, western Africa

Patricio Robles Gil / Pygmy Hippopotamus (Hexaprotodon liberiensis) grazing, Ivory Coast, western Africa

ZSSD / East African River Hippopotamus (Hippopotamus amphibius kiboko) portrait underwater, native to Africa

ZSSD / East African River Hippopotamus (Hippopotamus amphibius kiboko) baby underwater, native to Africa

ZSSD / East African River Hippopotamus (Hippopotamus amphibius kiboko) baby being nudged by mother underwater, native to Africa

ZSSD / East African River Hippopotamus (Hippopotamus amphibius kiboko) underwater, native to Africa

ZSSD / East African River Hippopotamus (Hippopotamus amphibius kiboko) baby examining mother's open mouth underwater, native to Africa

ZSSD / Pygmy Hippopotamus (Hexaprotodon liberiensis) portrait, native to West Africa

Shin Yoshino / Hippopotamus (Hippopotamus amphibius) pair fighting, Masai Mara, Kenya

Mitsuaki Iwago / Hippopotamus (Hippopotamus amphibius) pair nuzzling in water, Serengeti National Park, Tanzania

Gerry Ellis / Hippopotamus (Hippopotamus amphibius) mother and baby emerging from water lettuce in river, Serengeti National Park, Tanzania

Winfried Wisniewski / Grey Heron (Ardea cinerea) standing on sleeping Hippopotamus (Hippopotamus amphibious) in river, Africa

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) warning sign along road near Nelspruit, South Africa

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) yawning, Botswana

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) pair fighting in water, Botswana

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) two interacting, Khwai River, Botswana

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) two interacting, Khwai River, Botswana

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) large bull threat-yawning in the Khwai River, Botswana

Richard Du Toit / Yellow-billed Oxpecker (Buphagus africanus) small flock on Hippopotamus (Hippopotamus sp), Khwai River, Botswana

Shin Yoshino / Hippopotamus (Hippopotamus amphibius) group in water with Flamingos (Phoenicopterus sp) wading nearby, Ngorongoro Crater, Tanzania

Shin Yoshino / Hippopotamus (Hippopotamus amphibius) group in water, Masai Mara, Kenya

Shin Yoshino / Hippopotamus (Hippopotamus amphibius) mother in water with baby riding on her back, Masai Mara, Kenya

Gerry Ellis / Hippopotamus (Hippopotamus amphibius) mother and baby, Serengeti National Park, Tanzania

Shin Yoshino / Hippopotamus (Hippopotamus amphibius) pod at water's edge, Masai Mara, Kenya

Thomas Mangelsen / Hippopotamus (Hippopotamus amphibius) mother and young resting on riverbank with a Red-billed Oxpecker (Buphagus erythrorhynchus), Lake Manyara National Park, Tanzania

Gerry Ellis / Hippopotamus (Hippopotamus amphibius) pair swimming in water lettuce, Serengeti National Park, Tanzania

Gerry Ellis / Hippopotamus (Hippopotamus amphibius) group in river at sunset, Moremi Wildlife Reserve, Linyanti River, Botswana

Gerry Ellis / Hippopotamus (Hippopotamus amphibius) group soaking in Linyanti River, with rainbow in the background, Moremi Wildlife Reserve, Botswana

Gerry Ellis / Hippopotamus (Hippopotamus amphibius) close-up portrait of face, Sub-Saharan Africa

Tim Fitzharris / Hippopotamus (Hippopotamus amphibius) breathing at water surface, Kenya

ZSSD / East African River Hippopotamus (Hippopotamus amphibius kiboko) mother and baby underwater, native to Africa

ZSSD / Hippopotamus (Hippopotamus amphibius) with mouth open in threat display, native to Africa

ZSSD / Hippopotamus (Hippopotamus amphibius) mother and baby swimming in water, native to Africa

Mitsuaki Iwago / Hippopotamus (Hippopotamus amphibius) trio laying in mud beside a river, native to Africa south of the Sahara Desert

Mitsuaki Iwago / Hippopotamus (Hippopotamus amphibius) nursing young while Cattle Egrets (Bubulcus ibis) perch atop their backs, Sub-Saharan Africa

Murray Cooper / Hippopotamus (Hippopotamus amphibius) and Nile Crocodile (Crocodylus niloticus) pair on riverbank, Sabie River, Kruger National Park, South Africa

Paul D Stewart / Illustration of skeleton of a hippopotamus, (Hippopotamus amphibius) skelton, copperplate engraving from Cuvier's 'Ossamens Fossiles'. Cuvier saw that the key to understanding fossils was to relate th...

Konrad Wothe / Hippopotamus (Hippopotamus amphibius) pair coming ashore, Lake Tanganyika, Mahale Mountains National Park, Tanzania

ZSSD / East African River Hippopotamus (Hippopotamus amphibius kiboko) female getting sprayed, native to Africa

ZSSD / East African River Hippopotamus (Hippopotamus amphibius kiboko) playing with calf, native to Africa

Richard Du Toit / Hippopotamus (Hippopotamus amphibius) and Grey Heron (Ardea cinerea), Kruger National Park, South Africa

Suzi Eszterhas / Hippopotamus (Hippopotamus amphibius), northern Botswana

Mark Moffett / Hippopotamus (Hippopotamus amphibius), Selinda Reserve, Okavango Delta, Botswana

ZSSD / Hippopotamus (Hippopotamus amphibius) mother and calf, native to Africa

Kevin Schafer / Hippopotamus (Hippopotamus amphibius) mother and young, Queen Elizabeth National Park, Uganda

Shin Yoshino / Hippopotamus (Hippopotamus amphibius) pair fighting in water, vulnerable, Masai Mara National Reserve, Kenya

Suzi Eszterhas / Hippopotamus (Hippopotamus amphibius) two week old baby resting atop it's mother along the river bank, Masai Mara National Reserve, Kenya

Suzi Eszterhas / Hippopotamus (Hippopotamus amphibius) two week old baby yawning as it rests atop it's mother along the river bank, Masai Mara National Reserve, Kenya

Mitsuaki Iwago / Hippopotamus (Hippopotamus amphibius) pair cross grassland, Serengeti National Park, Tanzania

Konrad Wothe / Hippopotamus (Hippopotamus amphibius) defecating in the water, Aquatic Sub-Sahara Africa

Konrad Wothe / Cattle Egret (Bubulcus ibis) group resting atop floating Hippopotamus (Hippopotamus amphibius), Ngorongoro Crater, Tanzania

Gerry Ellis / Hippopotamus (Hippopotamus amphibius) group in river at dawn, Moremi Wildlife Reserve, Linyanti River, Botswana

Konrad Wothe / Hippopotamus (Hippopotamus amphibius) surfacing in river, Botswana