Tracing the Source of the Elephant And Hippopotamus Ivory from ...

wide, straight lips of the hippo enable it to graze so close to the soil surfaces that, as
Clemens and Maloiy (1982: 151) point out, considerable amounts of soil is inadvertantly
consumed, thereby strengthening the argument for unselective feeding. Nevertheless,
Eltringham (1999: 78, 80-81) suggests that, despite the unselective physiology and
feeding behavior, the hippopotamus does exhibit preferences since the types of plants
ingested are not in proportion to their occurrence in the natural environment. The hippo
may not select for grass species, per se, but rather selects the patches of grass sward in
which to feed. Swards are usually composed of only a handful of grass species and the
grazing activity of hippos creates an environment which favors the growth of short and
creeping grasses. The lips of the hippopotamus are adept at breaking off the short and
creeping grasses from the ground, whereas course tussock-forming grasses are difficult to
break off as they slip between the lips. Fortunately the short and creeping variety are
what the hippo favors and they tend to grow aggressively, effectively pushing out other
species less agreeable to the hippopotamus.
Several studies have investigated the specific species of grasses in the diet of the
hippopotamus. Field (1970, 1972; cited in Eltringham 1999: 79-81) analyzed the
stomach contents of the hippos in Queen Elizabeth National Park (Uganda) owing to
culling operations, and determined that some species were selected while others were
avoided. Such distinctions were made by comparing the percentage of the plant species
within the hippos’ stomachs with the percentage of the plant species in the natural
environment. If the percentage within the stomach is significantly more than within the
grassland then the species is said to be selected or preferred, whereas if the percentage
within the stomach is less, then the species is avoided. There were, furthermore, seasonal
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