How heavy is a hippo?

The common hippo is one of the heaviest land animals, behind only elephants and the white rhino (whose bulls average about 2,300 kg). San Diego Zoo Wildlife Alliance, using figures from the hippo expert Hans Klingel, gives an average of 1,546 kg (3,408 lb) for adult males and 1,385 kg (3,053 lb) for females. Norman Owen-Smith’s 1992 book Megaherbivores gives similar means of 1,480 kg for bulls and 1,365 kg for cows.

Our figure of 1.5 tonnes is an average adult bull. Males seem to keep growing all their lives, so old bulls are the heaviest, while females stop gaining at around 25 years old. An adult stands about 1.5 m (5 ft) at the shoulder and can be up to 5 m (16 ft 6 in) long, so most of that weight sits in a low, barrel-shaped body on short legs.

There is a second, much smaller species. The pygmy hippo of West African forests weighs only 179 to 273 kg (395 to 601 lb), roughly a sixth of a common hippo.

Guinness World Records lists the hippo as the heaviest even-toed hoofed mammal and says it can weigh in excess of 2,600 kg (5,800 lb). Owen-Smith reports exceptionally large males reaching 2,660 kg (5,860 lb). Jonathan Kingdon’s East African Mammals (1979) gives higher maximums of 3,200 kg (7,100 lb) for a male and 2,344 kg (5,168 lb) for a female.

Bigger numbers are easy to find. Guinness notes that an upper limit of 8,000 lb (3,630 kg) “is based on a historical rough estimate” rather than a real animal. Several books and websites, including San Diego Zoo’s public animal page, give males up to 4,500 kg (9,920 lb), but the zoo’s own library fact sheet appears to trace that figure to a 1959 source and says it may not be accurate.

Hippos spend most of the day in water, yet they cannot swim or even float. Their limb bones are unusually dense, with the hollow middle packed with bone, which makes the whole body heavier than the water it pushes aside. Instead of swimming, a hippo walks along the bottom or pushes off it in a slow-motion gallop. Adults can stay under for 5 minutes or more, though the average dive lasts about 104 seconds.

In 2009, Beth Coughlin and Frank Fish filmed two female hippos of about 1,360 kg each at Adventure Aquarium in New Jersey. Underwater they moved in bounds, with all four feet off the bottom for part of each stride, and they came back down with an acceleration about 92% lower than gravity on land. The researchers compared it to moving in microgravity: a gait that would be unstable for a 1.4 tonne animal on land becomes easy when the water carries most of its weight.

A newborn hippo weighs 25 to 55 kg (55 to 121 lb). Calves are born on land or in shallow water; if one is born underwater, its mother pushes it to the surface to breathe. They can nurse underwater, with ears that fold and nostrils that close, and are weaned at 6 to 8 months.

The most famous exception is Fiona, born at the Cincinnati Zoo on 24 January 2017, six weeks early. She weighed just 13 kg (29 lb), about half the lowest birth weight recorded for the species before her, and was too weak to stand or nurse. Bottle-fed and given round-the-clock care, she passed 1,000 lb (454 kg) in December 2018, still only about a third of the weight of an adult female.