 Reference Base  Further attempts to determine the food habits of the Indi... |
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| Location: |
Asia - South Asia - India - Assam |
| Subject: |
Ecology - Food |
| Species: |
Indian Rhino |
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Kaziranga, Assam. In an earlier communication (Brahmachary et al. 1971) the attempt to determine the food habits of the Rhino in Jaldapara, was described. It was c oncluded that observing the microscopic sections of the vegetal remains in the dung was a good technique, especially for Jaldapara or other similar places where direct observation is difficult due to the nature of the terrain and vegetation.
The present report describes results of a study in Kaziranga during about a fortnight in January, 1972. Unlike at Jaldapara, direct oservation at Kaziranga turned out to be very simple because one can approach the rhinos to very close quarters, while mounted on elephants and the grass being short in certain seasons, the actual grass species fed on by the rhinos can be noted. Over the years the mahouts have also noticed these grasses and plants so that the food habits are largely known. The following are our findings.
Plants germinated in the dung:
This, according to us, is the most important result of the present study. Old dung balls, examined on breaking open, revealed plants germinated inside them. We did not examine the old dung balls in Jaldapara and therefore missed this aspect. At Arimora (Kaziranga) startlingly large numbers of grass stems, producing roots and stems leaflets at nodes, were found inside the dung balls. We also detected two dicot seedlings. As we were not equipped for carrying to Calcutta and cultivating them, we tried to bring only a few packed in a very small tin container and practically none survived the ordeal.
Only one grass stem with leaves, on being transplanted to a pot in Calcutta, grew up to a certain small but detectable size. Although precise identification is not possible.under these circumstances, this grass seemed to be almost certainly Cynodon dactylon. one of the common lawn grasses. Practically all other grass stems germinated inside the dung balls at Arimora were of a different type. They were certainly of the creeping type and from the description 'rooting at nodes' by Mahanta and Neog (1968) seem to 'Alaijabari' (Drymaria cordata).
The interesting point about this preliminary observation is that this can be developed into a technique for determining the habits in terrain where direct observation is difficult or impossible for, the plants can be cultivated locally, in pots or in plots of garden; secondly, the implication points out a new means of dispersal for grass and is therefore of ecological importance. Bor (1960) describes the different mechanisms for dispersal of grass through animal agents but dispersal through alimentation has not been considered probably because the herbivores in general (like cattle or deer) digest the grass thoroughly. The rhino and the elephant pass on large undigested pieces through their alimentary canal and into the dung. We did not find germinating grasses inside the old elephant dung but the large quantities observed in rhino dung effectively prove that this animal plays a role in the dispersal of grass.
Solanum khasianum (Ban-Begun) is often found to grow around rhino dung, as has also been noticed by the local people. We noticed 20 cases of such luxuriant growth of this plant around rhino dung Not a single case of such growth was found in the few plants noticed in places where no dung had been excreted. We also assured that the young plant were growin. from inside the dung ball, and not from the soil below. Birds can also drop the seeds, accidentally, on the fresh dung but this is unlikely in so many instances. T'he Rhino, therefore, seems to act as an agent for dispersal and concentration of this plant. Apparently, the dung also acts as a source of manure and/or moisture, which in turn may -affect the, chemical contents of the plant like solasodine (see later).
Direct observation
We observed Rhinos feeding voraciously on Flemingia lineata, a small shrub. Even plants partially burnt black and apparently totally dry were plentifully eaten. This is the only non-grass species we could directly observe during the actual process of eating. The prehensile upper lip is very handy in manipulating such shrubs and clumps of tall grasses.
The rhnos fed on almost all the grassy growths, the very short grasses creeping on the soil as well as tall grasses from part of their menu. All these grasses can easily be identified if the inflorescence is available. We could collect inflorescence of the following 11 species while Mahanta and Neog (loc.cit.) list 26 species of common grasses. Attempts at other seasons, in particular early monsoon, would not be very fruitful for collecting the remaining species:
local name
1. Imperata cylindrica ulu
2. Eragrostis gangetica
3. Cyperus rotundus
4. Vetiveria zizanioides (see below)
5. Aristida cyanantha
6. Sporobolus diandra
7. Chrysopogon aciculatus bonguti
8. Thysanolaema phragmites
9. Rhynchospora aurea
10. Unidentffied
11. Arundo donax Nal
One of these, locally known as Birina, was identified by the Botanical Survey of India, Calcutta, as Vetiveria zizaniodies although according to Mahanta and Neog it is Erianthus elephantius
Examination of vegetal remains in the dung
It is well known at Kaziranga that the rhinos now plentifully eat Water Hyacinth. We also detected numerous remains of water-hyacinth strips in various dung balls near the marshy places.
More than 1500 undigested stems were collected from various dung balls but it became soon apparent that the technique of examining the microscopic sections of these remains would be unnecessary in case of the openland rhino at Kaziranga. Unfortunately very few stems in good condition were found in the dung balls collected from the woodland. Of the 12 stems which allowed sectioning only 3 were dicot species.
Chemical studies.
It is of great interest to study the nutritional and other chemical aspects of the local plants consumed by the wild animals. Apart from the question of wild game management, such studies might lead to the discovery of superior food for domestic livestock and of useful drugs. Mahanta and Neog sum up the data on total nitrogen content, mineral content etc. in some of the commoner grasses of Assam. An important new aspect of study will be the estimation of certain amino-acids like lysine, cystein, methionine etc. Lysine-rich corn or wheat has appeared as a great boon. Harpstead (1971) reviews the experiments on lysine-rich corn and shows how it may spell the difference between life and death. Leaf protein is however rich in lysine (unlike seeds, grains, etc.). Again, in certain grasses, TCA-soluble and TCA-insoluble nitrogen are about equal amount, so that free amino-acids are present in large quantities and are therefore worth estimating.
These studies can be carried out only in a local laboratory but we have made some preliminary tests with the leaves of solanum and lawn grass (Cynodon dactylon) obtained from the outskirts of Calcutta (which may thus differ from the Kaziranga samples). One dimensional paper chromatography showed only one or two large free pools of amino-acids in solanum leaves while 5 such pools were traceable in Cynodon. With 2-dimensional chromatography, the latter would probably resolve a larger number of amino-acids. None of these amino-acids seemed to coincide with 'marker' lysine.
Remarks:
Laijahari grass (Dtyinai.ia cordata) is the richest in calcium the Assam grasses which are generally calcium poor (Mahanta & 1968). It is good that rhinos eat this species plentifully.
Water-hyacinth is not a very good food for its dry weight is only about 9-10% and of that about 10% is protein. Good grass is preferable to this pestiferous weed.
Cynodon dactylon (dub or lawn grass) can produce HCN under certain conditions of drying so that in certain year such as of extreme drought, places with extensive growth of this grass should perhaps be burnt off.
Solanum khasianiim has gained some reputation as the source an alkaloid (solasodine) which may act as a precursor of steroid hormones and as such may be of interest as a commercial source for drug manufacturers. As manuring has an influence on the alkaloid content, the vigorously growing plants around the rhino dung are worth studying.
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