Jachman, H., 1984. Status of the Mwabvi rhino (Diceros bicornis). Nyala 10 (2): 77-90, figs. 1-8, table 1
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| Location: |
Africa - Southern Africa - Malawi |
| Subject: |
Ecology - Census Methods |
| Species: |
Black Rhino |
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Malawi, census by measuring rhino droppings. Rhino tend to scatter their droppings with their hind-feet, fortunately often missing some of the boli, which can be measured for circumference. The area directly west of the camp (about 1 km) was solely used by rhinos 1 and 2, for which two ranges of boli-circumference measurements were found. For rhino 1, circumference measurements ranged from 36 to 38 cm and for rhino 2 from 40 to 43 cm. It is striking that the distribution of circumference values for both rhinos is skewed. We can interpret this as follows; during the latter part of the dry season, rhino mainly eat woody browse and some leaves. A maximum intake of highly fibrous material will stretch the intestines, producing boli with a maximum circumference. A lower intake of food in general or a larger ratio of digestable to fibrous material will produce boli with a slightly smaller circumference. Hence the distribution of bolus circumference values per rhino will always be skewed, with a maximum value decreasing to a minimum value, both depending on the quality of the diet. Of the total sample, a large percentage of boli belonged to rhinos 1 and 2, solely because the area next to the camp was surveyed more thoroughly than the rest of the Reserve. Fresh footprints next to fresh droppings were also found of rhino 3, leaving the remaining circumference values for rhino 4. In order to check on the method, the mean bolus circumference value was plotted against the mean fore-foot diameter for rhinos 1 to 4. Regression analysis was applied and the relationship appeared to be highly significant (P < 0.001, r = 0.997; y = 0.384x + 6.456), supporting the results of both the footprints and droppings method. The remaining boli with circumference ranging from 26 to 27, 29 to 30 and 32 to 34 cm belong to rhino 5 and one or perhaps even two more unidentified young rhino. A fore-foot diameter of 18.2 cm (rhino 5) would give a mean bolus circumference of 30.8 cm (Fig. 6), located halfway between the second and third peak of the second-order average in Fig. 5. This would imply that rhino 5 is possibly represented by a bolus circumference range of 29 to 34 cm, which;. seems unlikely given the circumference ranges of rhino 1 to 4. Therefore we reject 18.2 cm as fore-foot diameter of rhino 5, but maintain 16.5 cm as either fore- or hind-foot diameter. Using the droppings method, we may conclude that Mwabvi Reserve contains 6 or 7 rhino.
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Status of the Mwabvi rhino (Diceros bicornis)
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