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Hippos of the Black Volta River Print E-mail

Map 6. BLACK VOLTA RIVER IN BUI NATIONAL PARK SHOWING STUDY SITES,  SITES OF HIPPO SIGHTINGS AND FEEDING AREAS.

Because of the lack of individual identification, little can be said about daily movement patterns of hippo groups. Local fishermen claimed that areas of rapids (even very fast white water such as Fagoo) present no obstacle to hippos, who often simply walk through these areas. The main obstacle to hippo movement is dense vegetation, which may limit their movements away from the river to areas of more open forest and grassland.

Of nine foraging zones identified as "hippo lawns" eight were on the western riverbank (Map 6)  Area of these zones was estimated by eye. The steep topography of the Northern bank must be at least partly responsible for this trend. It is presumed that steep hillsides are not suitable for hippo foraging, regardless of their vegetation types.

Observations on hippos in late afternoon and early evening suggest that large males leave aggregations before dusk and presumably forage away from the rest of the group. Based on the numbers of hippos tracks leading to and from the river, most animals in one group must leave the water by the same route, although thereafter they may disperse to forage.  Following tracks made by foraging hippos was relatively easy, but because animals tend to use previously established tracks it was not possible to estimate mean nightly distance travelled. Some tracks indicated that a single large individual (presumably the mother) foraged with a very small individual at least twice over a ten day period in the vicinity of the Coco Stream.

Attempts at observing hippo foraging behaviour were not successful. Nocturnal censusing of the type described by Ogen-Odoi and Dilworth (1987) is inappropriate for this area because hippos are not accustomed to vehicles (or engines of any type). Two tree houses were built in an area that appeared to be a major foraging ground for hippos. The buildings were constructed over six days and thereafter were manned nightly. No hippos were seen from the treehouses, although on some nights they could be heard nearby,  in or at the edge of, the river. It is likely that the disturbance caused by treehouse construction deterred the hippos from foraging in this area.

Because it was not possible to deduce how many animals had been feeding in any location, measurements of the total feeding area (i.e. the area of "hippolawns") are not meaningful. Attempts to measure footprint size and therefore assign spoor to individual animals were not successful, probably because of differential shrinkage of footprints depending on the moisture content of the mud.

Two excursions on foot further upstream (to Abru Bhunu) suggest that hippopotamus density increases further into the park This is based on the higher incidence of tracks seen and the fact that wherever the riverbank was accessible hippos could be seen or heard. Although it was not possible to make estimates of numbers in these areas, desnities appeared to be much higher than in surveyed areas of the river.

During riverbank surveys it was noted that hippos tended to remain in one place for at least several hours at a time. They are much easier to see when they are resting than when they are travelling through the water. In the latter case their presence is usually revealed only as a distinctive zigzagged wake.

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Above & below: The hippos of Bui photographed with a 600mm lens on 800ASA film.

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