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November 2001

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Kenya's Mzima Spring Comes Alive

By Mark Deeble and Victoria Stone
Mzima. The word means "alive." Yet the life of Kenya's Mzima Springs is largely born of ash and dung. In the neighboring Chyulu Range stand porous peaks of volcanic ash, whose youngest cones formed about 500 years ago. Rising 7,000 feet (2130 meters) above an arid plain, these hills trap up to three feet of rain each year from moisture-laden winds. All that rain soaks into the sponge-like ash and percolates down until it hits impervious bedrock and begins its underground journey to Mzima Springs, some 25 miles (40 kilometers) away. Filtered over many years, the pure water gushes forth at a steady pace of more than 50 million gallons (190 million kilograms) a day, creating an oasis at the heart of Kenya's Tsavo West National Park. We camped there for two years with our two young sons, studying Mzima's hippos, whose copious deposits of dung nurture a pyramid of life.

Cool and shallow, a shaded spring offers buoyant relief to a herd of ponderous hippos, one of four groups that loll all day in the protected waters of Mzima's three main pools. By night the hippos graze on nearby grasslands. When they return, their yellowish waste fertilizes the water with vital organic matter.

Nostrils pinched to block out water, an adult hippo stands in a wreath of dung stirred by its footsteps. The consistency of chopped wet hay, the dung provides a hiding place for predatory insects and food for snails and fish. Insects, fish, birds—one feeds the next in an intricate chain anchored by the bulky herbivores that can eat more than a hundred pounds of grass a night. After death, hippos themselves provide food for scavengers like turtles, which lay their eggs on Mzima's shore. There, in wet-season puddles, shaggy coats of algae sprout on the shells of juveniles. When the turtles later enter the springs, tiny Garra fish mow the shells clean.
One Garra became a meal for a water scorpion. The insect hid in hippo dung, then ambushed the fish, snatching it with raptorial forelegs. Larger fish are the favored quarry of the rare African darter, or snakebird, which cocks its neck and strikes like a serpent to spear prey.
It took nearly a year of trial and error with various gear to begin to capture our own quarry—photographs of rarely seen behaviors among Mzima's wildlife.
In the vulnerable first months of life young hippos rely solely on their mothers for defense against crocodiles, virtually the only predatory threat at Mzima. Once a hippo reaches one year, it is robust enough to stand its ground and is rarely bothered.
Hippos display almost whalelike adaptation to life in the water. Infants may be born in water and will even suckle there, raising their heads from time to time to breathe. After a secluded period of bonding, mother and calf will return to the herd, usually composed of a dominant male, cows, and calves of both sexes.
For decades the number of hippos at Mzima Springs has remained constant at 60 to 70 animals. Blessed with a steady flow of water, the springs are spared seasonal fluctuations that can stress populations and prompt crowding and fights at drying pools. We saw no fights, but we did see an infanticide, one of only a handful documented. It was doubly rare because the attacker was not the dominant male but a young hippo, which repeatedly bit and dunked a newborn male until it died. The distressed mother carried off the carcass. It's possible the aggressor was a male trying to eliminate a future rival.
Like a jowly king at ease with his attendants, a hippo passes with a retinue of fish. It has long been known that hippos and fish are constant symbiotic companions. Fish clean hippos and are in turn nourished by the algae, parasites, and dead skin scraped from hippos' hides. What wasn't known—and what we photographed for the first time via remote submerged cameras at Mzima—amazed us.
We discovered that certain fish specialize in cleaning specific body parts. The ubiquitous Labeo, in the carp family, is the main cleaner, using its wide rasping mouth to scour a hippo's hide. Barbus feeds directly on dung and cleans the cracks in the soles of the feet. Small cichlids graze around the tail bristles. And tiny Garra cleans out wounds.
Hippos are far from passive recipients of these services. We saw them deliberately splay their toes and spread their legs to provide easy access or to solicit cleanings. They would even visit "cleaning stations" where fish congregate—much like pampered clients going for a massage or manicure at a spa.

Gloriously clear and inviting, this nameless spring about 50 miles (80 kilometers)  west of Mzima lured us for a dive. We discovered and entered a narrow cave opening. Inside a labyrinth of blind tunnels we found scores of jumbled hippo, crocodile, and turtle bones, some so old they crumbled at our touch. Clearly the spring once held hippos and all their attendant life, but today its waters are nearly lifeless.

Clues to the cause of this sterility can be found just beyond the spring's steep banks. The surrounding landscape, which lies outside a national park, is crowded with small subsistence farms. Hippos likely would have eaten or trampled crops during nightly grazing forays. We assume that farmers chased off the hippos or killed them for meat. Without hippos and their dung, the spring died. As for the bones, we speculate that hippos occasionally blundered into the cave, became disoriented, and drowned. Attracted by the smell, crocs followed and met the same fate.
Safely ensconced in a national park, Mzima should be spared the starkness so apparent just beyond its borders.


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