Sumatran rhinoceros, Dicerorhinus sumatrensis (Fischer, 1814), in the Gunung Leuser National Park, Sumatra, Indonesia : its distribution, ecology and conservation

The Sumatran rhino is solitary for most of its life. The home range of a rhino overlaps with the home ranges of several other rhinos and animals occasionally meet, but they do not stay together for any length of time. It may be that young sub-adults, in their first years of independence, form loose associations occasionally, but later they travel alone, wandering round their vast home ranges. A male and female seem to come together for only a short period for mating. Non-breeding females may have very little contact with other rhinos, because they occupy a relatively small range and leave it only occasionally to visit a saltlick.The adult males seem to be more actively searching for contact. They cover a large area and are very active around the saltlicks, apparently searching for signs of other rhinos. Although males have more frequent contact with other rhinos, they never associate with an other rhino for more than a few days. If longer-lasting bonds were usual, the tracks of two or more animals walking together would be found more frequently.A rhino calf remains close to its mother till they separate. When very young the calf stays very close, but older calves do not wander more than a few metres away from the trail of the cow. When the calf is about 16 to 17 months old it separates from the cow. Maternal care for the young is limited to the infant's period of rapid growth, and when the youngster has reached about three-quarters of the adult size, it leaves the cow. There may still be occasional contact between the cow and her independent offspring, but most of the time the young rhino travels singly.While nursing a calf the female rhino moves from her non-breeding range higher on the slopes, to the vicinity of a saltlick. Already during pregnancy the females may make more frequent trips to the saltlicks. The calf is probably born close to a saltlick and during the whole period of nursing cow and calf remain in a relatively small area, about 10 to 15 sq km, around one of the licks. The pair visit the lick about once every three weeks, about two to three times as often as non-breeding females and sub-adults. When there are several females with a calf around one saltlick, their ranges usually overlap and the pairs may meet occasionally. Tracks criss-cross the area, and several routes are used to approach the saltlick.After leaving the cow the calf remains in the area where it was nursed. The cow returns to her non-breeding range, further away from the saltlick. The newly independent rhino, the young sub-adult, initally uses a relatively small area, 10 sq km or less, part of the range it used with its mother. The young rhino roams over the area intensively, often returning to the same places; it seems as though the animal is familiarizing itself with the location. The animal gradually extends its range into adjacent areas, where it was never found with the cow. For at least two or three years the young sub-adults remain in the neighbourhood of the place where they were born and nursed. During this time they grow slowly, and after about three years their footprints are still smaller than those of an average adult and clearly recognisable as from a young rhino.The older sub-adults, aged at least six or seven years by the end of the study occupied relatively large ranges and many were only found occasionally. Animals gradually extend their home range for a number of years with older sub-adults travelling widely into new areas, probably to find a gap between the existing adult ranges. It seems to take several years before a Sumatran rhino is adult and has established a permanent home range. A young rhino remains in the 'nursing area' till it is at least four years of age and it is probably not sexually mature before the age of 7 or 8 years.The adult rhinos have permanent home ranges which are spread rather evenly over the study area, with the centres of the home ranges on the major ridges. The non-breeding females remain in relatively small ranges, no more than about 10 sq km, on the higher parts of the ridges, away from the valleys and the rivers. The tracks of non-breeding females were rarely met, usually only when the animals visited a saltlick and it appears that these normally travel little along the large game trails, perhaps once every 6 weeks to visit a saltlick. The rhino then follows a specific route to the saltlick and returns to its home range immediately, usually along the same route.The ranges of the females in the non-breeding period seem to be well separated and the records do not show any overlap in range, except close to the saltlicks. The paucity of records for non-breeding females makes it difficult to draw firm conclusions, but it seems that they have more or less exclusive territories. It is not clear how the spacing of the female home ranges is accomplished, but it may be that females tend to avoid areas where other females have left tracks and signs. Nursing mothers with calves do not avoid other female's tracks in the vicinity of the saltlick.Although we have no precise records it seems that the interval between births is at least 3 to 4 years, somewhat longer than the time that a female carries and nurses a calf. It may be that the long birth interval is necessary for the female to build up sufficient reserves for another reproductive effort. Although rhino food plants are abundant, they are not particularly rich in nutrients and minerals and the female probably needs a period of limited mobility and seclusion to recover condition between births.Adult males range over much larger areas, 25 to 30 sq kin or more. It seems that male home ranges have a core area where most activity is concentrated. Peripheral areas are visited less frequently and then the animal often follows the game trails for long distances. On average males visit the saltlicks about as often as sub-adults and non-breeding females, but males with ranges close to the lick, visit them much more often. From the saltlicks males usually make several forays in different directions, giving the impression that they are searching for other tracks. Males visit a regular saltlick, but may occasionally also travel to other licks.Male ranges overlap considerably, but it appears that the core areas are distinct and rather evenly spaced over the area. There might be some form of hierarchy among males, because some animals make more marks along the trails than others. Visual and olfactory signs are left by rhinos along the large game trails. They include soil scrapes, faeces, sprayed urine and bent or twisted saplings, in various combinations. All rhinos mark in this way, both males and females. Young sub-adults rarely mark, while the older sub-adults are the most active markers of all groups. Marking may be associated with the process of establishing a permanent home range. The more complicated signs, those consisting of soil scrapes, bent saplings, faeces and/or urine are usually only made by males, and could indicate male territoriality.Saltlicks are an important focal point for rhinos in the Mamas study area. Each lick is visited regularly by several rhinos, and each rhino appears to visit one particular saltlick, not always the one closest to the centre of its home range. A rhino generally uses one particular route to the licks, following it consistently on every visit. Each of the six saltlicks discovered in the study area is used by 5 to 7 different rhinos, each animal visiting a lick on average 6 to 7 times per year. The consistency with which a rhino visits a certain lick suggests that all rhinos using a saltlick may be related. Sadly many rhinos also end their life near a saltlick, because hunting activities are centred at these places.Rhinos drink mineral-rich water at the licks most probably to compensate for a deficiency or imbalance in the mineral composition of the food. In a number of samples of plants eaten by rhinos, the sodium (Na) concentration was found to be very low, also the phosphorus (P) concentration, especially in relation to the calcium (Ca) concentration, was low. If there is a deficiency it is probably in me of these elements. The mineral concentrations in the water of the saltlicks vary considerably. All have about 100 times more sodium than surface water, but the concentration of phosphorous varies between the licks. The amount of minerals that a rhino may imbibe at each visit to a lick is small, less than in a day's intake of fodder. So it is not clear how important one visit a month is for maintaining the animals mineral balance. It is more probable that for adult rhinos the social function of a lick, as a place for meeting other rhinos, is more important than the extra minerals.The daily movements of the rhino seem to be controled by the terrain, and on the slopes they follow the contours or ridges. The larger rivers are important boundaries for rhino. Rhinos have no problem in crossing the rivers, and do so frequently, but they usually do not stay on the other side, but recross the river. The bigger the river the more important it seems to be as a boundary, and the Mamas river forms the boundary of the home range of almost all known individuals. The tracks of only two older sub-adults were found on both sides of the river. The big game trails on the ridges are more often used by the rhino for climbing than descending. This and the habit of turning back at the major rivers, means that a wandering rhino automatically turns back to the centre of its home range, which is usually located on one of the main ridges.When not following a trail the rhinos more or less follow the contours of the slope, crossing small streams and minor ridges. Animals often follow wide trails for some distance or may levae it to wander over the slopes. As they travel rhinos browse or take a mudbath in a wallow. Faeces and urine are found along the animal's trail and occasionally the rhinos lie down.The Sumatran rhino feeds on leaves and twigs of a great many plant species. Fallen fruits are also taken, but these were rare in the Mamas area. When feeding the animal moves in a zigzag fashion through the forest, often going around in circles, browsing on the soft parts of the plants within its reach. Periods of feeding alternate with periods of travel, when the animal often walks several kilometres without feeding, except for an occasional bite from a plant along the trail. When feeding the rhino seems to prefer places with a dense undergrowth of soft, juicy plants. In the mountain forests of Gunung Leuser there is very dense undergrowth along the streams and on the lower slopes, and these seem to be the favoured feeding places. Rhinos also feed on the young regrowth on landslides and at tree falls. Where there is less undergrowth the rhino feeds on small saplings, pushing them over to browse on the crowns, but this type of food appears to be less favoured and also contains less nutrients and minerals. Feeding occurs mainly at night and in the early morning.Rhinos feed on a great many plant species taking only a little material of anyone species. The rhino does not appear to be selective while feeding, but a few species seemed to be favourites, while others, like wild bananas, are ignored. There seems to be abundant food for the rhino in the upper Mamas. Over a large part of the area the forest supports dense undergrowth with numerous accessible saplings. The standing crop of rhino food plants is certainly large, but the production of new growth is very slow. An area that has been browsed and trampled by rhino, takes a long time to recover. This might explain the need for the continuous travels of the rhino. Although productivity is low in the understory there seems to be considerably more food available than can be consumed by the present rhino population (estimated at 13 to 14 rhinos per 100 sq km), and it is probably not the quantity but the quality of the food that is a limiting factor for the population.Rhino faeces are often dropped in streams or along the rhino's trail. The faeces, with characteristic twig fragments, remain visible for a long time, especially at the higher altitudes. The Sumatran rhinos prefer to drop their faeces close to other faeces, but large dung piles are not made. All animals, male and female, normally spray urine backwards over the vegetation.The wallows are a characteristic feature of any rhino area. The pits are often used for a long time and rhino's digging in the banks give the wallow a characteristic shape. It seems that a rhino takes a bath at least once a day and sometimes several times a day. Wallows are used day and night, but rhinos probably spend more time in wallows during daytime. Each wallow is used by several rhinos and on average the wallows along the main trails were used about 4 times per year.The major difficulty in interpreting the data was the disjunct and patchy nature of the records for most of the rhinos. For many individuals there were only few records, spread out over a long period of time; this not only made the identification of the plastercasts more difficult, it made it more difficult to draw conclusions about rhino behaviour and activity from the available data.The remoteness and inaccessibility of the area and our financial limitations made it impossible to maintain a permanent presence in the study area. Because this study focussed on tracks we decided to use the days in the study area to find as many tracks as possible. This required the survey team to keep on the move and left little time for more detailed study of single tracks. By following tracks for a longer period and distance one can discover much about the daily routine of the rhino, information that could only be gathered incidently in this study. Ideally one should monitor movements of the rhino over a large area and also follow single tracks for a number of days.Interpretation of the data is limited by the difficulties in ageing the tracks. One can only estimate the time and the duration of the various behaviours and activities of a rhino from very fresh tracks or when the animal is actually met. These occasions are very rare and normally one can only guess the approximate age of the tracks. Therefore track studies are of little value for studying the animal's daily rhythm, unless one can trail single animals for a few days. With very experienced trackers it is possible to follow a rhino closely, without disturbing it, but this requires a more permanent presence in the study area.