Hippopotamus amphibius: The River Horses of Lake Manyara, Tanzania

18 Jul
[ Blogger’s note: The following photographs were all shot during an extended stay in Tanzania and Kenya in February of 1988.  As they predate my use of a digital camera, these images were scanned from prints and cleaned up using Photoshop.]
 

Like most North Americans, the only hippopotamus (Hippopotamus amphibius) I’d ever encountered was a disembodied pair of huge nostrils, bulging eyes, and twitching ears protruding a couple of inches above the surface of the murky waters of a concrete pool in a zoo enclosure. My enduring impression of hippos was one of lethargic seldom-seen behemoths that spend their lives submerged and barely moving.

When my driver collected me at Serena Lodge earlier that morning, he said the day’s trip was to Tanzania’s Lake Manyara, about 3 miles south of the small town of Mto Wa Mbu. “Oh, yes… and we’ll stop to see a few hippos along the way.” So when our Land Rover pulled off the dirt track, I wasn’t prepared for the sight of a few hundred animated and actively socializing animals immersed in and occupying the banks of the Hippo Pond located a little inland from the northern shores of the lake!

Male hippo - Lake Manyara

A large male hippo warily scouts the frontier of his territory.
(Click on image to view a larger version.)

Because we arrived at the pond a bit after sun-up, we were treated to the sight of several individual hippos exiting the water to trundle off in different directions for some solitary foraging. These individual forays onto land are the only times that this wholly aquatic mammal leaves the water and the company of its fellow pod members.

walking hippo - Lake Manyara

This hippo has abandoned the cooling muddy water of his home pond to do a little early morning solitary foraging.
(Click on image to view a larger version.)

The hippopotamus is thoroughly adapted to its aquatic environment. It is able to thrive in its watery home by means of several unique behavioral and physical adaptations, about which zoologists and other mammalian researchers knew relatively little when I took the following photographs back in 1988. The following is a list of some of the more interesting and unusual adaptations.

  • Hippos are members of the Order Artiodactyla (even-toed ungulates) and the Infraorder Cetancodonta, the only living members of which are hippos (Family Hippopotamidae) and  whales and porpoises (Family Cetacea). This taxonomic relationship is based predominantly on genetic rather than physical similarities.
  • The common ancestor of hippos and cetaceans split off from the other Artiodactyls about 60 million years ago; the earliest fossil identified as a hippopotamus (Kenyapotamus sp.) is more than 15 million years old.
  • The eyes, ears, and nostrils of hippos are placed high on the roof of their skulls. This allows them to be in the water with most of their bodies submerged.
  • Hippos possess a very robust and highly specialized graviportal skeletal system that is well able to support their great mass (mature adults can reach more than 4.5 meters in length and weigh more than 1.8 metric tons). In addition, the water in which they spend most of their lives reduces the burden of excessive weight; this accounts for the hippo’s relatively short legs.
  • Its body’s specific gravity allows a hippo to be able to sink in fresh water so that it can easily walk at a good pace on the bottom of its home stream or pond, despite its relatively poor swimming and floating skills.
submerged hippos - Lake Manyara

The members of a dominant male hippo’s harem keep well submerged in the cool muddy water, allowing only their eyes and snouts above the surface.
(Click on image to view a larger version.)

  • A hippo’s skin is relatively thick (15 cm), but its subcutaneous fat layer is surprisingly quite thin. Its skin secretes a reddish-brown liquid that acts as both a strong sunscreen and natural insecticide.
  • Hippo males are extremely territorial, but only in water; on land they emerge individually to graze peacefully at a good distance from one another.
  • Mothers are extremely protective of their young and are always accompanied by them when they forage on dry land. A mother will ferociously defend her baby from any predator, including crocodiles and the occasional dominant male bent on eliminating his youthful competition.
male hippos - Lake Manyara

A dominant bull (extreme left side of photo) sees off a smaller rival, instigating a violent chase shortly after I snapped this picture.
(Click on the image to view a larger version.)

  • While defecating to mark their territory, male hippos spin their tails to distribute their excrement over a greater area.
  • Hippos are also retromingent (that is, they urinate backwards), making it easy to mark one’s territory while on land with a good strong stream of piss. I’m sure the ducks in the photo below have a wary appreciation of that hippo characteristic…  B-)
hippo & ducks - lake manyara

The big male in the foreground is the dominant bull along this stretch of lakefront. I counted about 20 other hippos that appeared to be females in his harem.
(Click on the image to view a larger version.)

  • Hippos mate exclusively underwater, both partners remaining submerged during most of the encounter, emerging occasionally to catch their breath.
  • Baby hippos are born underwater and weigh as much as 100 pounds (45 kilograms) at birth. The newborn must swim to the surface to take its first breath.
  • Young hippos often rest on their mothers’ backs when the water is too deep for them. Although babies commonly swim under water to suckle, they may also suckle on land when Mom leaves the water to forage.

Conservation Status

In 2012, Hippopotamus amphibius was listed as a VULNERABLE species on the International Union for Conservation of Nature’s (IUCN) Red List of Threatened Species. The world population is estimated at 125,000 to 150,000 individuals. Tanzania’s population is the largest at about 20,000-30,000 individuals. Hippos are declining steadily on the African Continent due to loss of habitat and the reduction of bodies of readily available freshwater. Hippos are also being taken by poachers as a source of “bush meat” and ivory (their tusks).

hippo carcass - Lake Manyara

The carcass (stripped clean by scavengers) of a recently killed hippopotamus. This rare sight allowed me to glimpse the impressive skull and mouth furniture of one of the most dangerous and aggressive animals of Sub-Saharan Africa.
(Click on image to view a larger version.)

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4 Responses to “Hippopotamus amphibius: The River Horses of Lake Manyara, Tanzania”

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  3. Deruiter 1 September 2014 at 11:02 AM #

    An outstanding share! I have just forwarded this onto a co-worker who had been conducting a little research on this. And he actually bought me breakfast due to the fact that I discovered it for him… lol. So let me reword this…. Thank YOU for the meal!! But yeah, thanks for spending some time to talk about this matter here on your web page.

  4. Frank Rice 26 July 2013 at 3:29 AM #

    interesting, Mike… I enjoyed the journey…

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