Rhino

Sumatran Rhinoceros

Dicerorhinus sumatrensis

 With over an 80% reduction in population size in just over five decades and still in decline, with fewer than 250 individuals left in the wild and one of its three critically endangered subspecies possibly extinct, with the remaining small populations separated, the Sumatran rhino Dicerorhinus sumatrensis worryingly jointly carries the title of the planets most endangered big mammal with the Javan rhinoceros Rhinoceros sondaicus.

The two Indonesian rhinoceros species, the Sumatran and Javan rhinoceros can easily be told apart from their physical characteristics (described more below) – the Sumatran rhinoceros is characterised by long reddish hairs and the possession of two horns.

Physical Description

The two horns, fringed ears, wrinkles around eyes, reddish-brown colour and a covering of long hairs distinguish this rhinoceros species from the others.  The Sumatran rhinoceros is the smallest of all currently living rhino species, with a length of 2-4 metres, height of 1-1.5 metres and a weight of 600-950kg! The existing subspecies of the Sumatran rhinoceros differ only at the genetic level.

Range and Distribution

The Sumatran rhinoceros once ranged from the Himalayan foothills in Bhutan through to the islands of Borneo and Sumatra.  However poaching for its horn (for use in traditional Chinese medicine and ornamental purposes) and habitat fragmentation (mainly through giving poachers easier access to the rhinos) has reduced this species to a very small percentage of its former range and population.  Its remaining range includes Sabah in Borneo (Tabin Wildlife Reserve) of which the Sumatran subspecies D. s. Harrissoni resides, and parts of Sumatra where D.s. sumatrensis currently resides.  Sumatra is the stronghold for this species where the majority of the remaining individuals of this species resides within Bukit Barisan Selata, Way Kambas and Gunung Leuser national parks.  Some individuals of the subspecies D. s. lasiotis may remain in northern Myanmar.

Ecology

 Diet & Behaviour- Sumatran rhinos are optimistic feeders consuming a broad variety of plant species (such as bamboo) in tropical forests – feeding on leaves, bark, twigs and fruit (especially wild mangos and figs).  They may occasionally move into cultivated crops to eat and will roam over large distances (5-10km) in search of salt licks.

Sumatran rhinos are mostly solitary animals (except when opposite sexes meet for courtship or when a mother is with its calf) living at low densities and are thought to be territorial.  Home range size is currently unknown but thought to be no more than 500ha for females and larger for males.  Adults are very traditional in their home ranges and will not move unless disturbed severely.

Life History- Every 3-4 years females give birth to a single calf (females are thought to become sexually mature at 6-7 years and males at 10 years); and in accordance with the regional rainy season (October-May).  Before leading solitary lifestyles, when calves become independent (after 16-17 months) they may join other juveniles.  The lifespan and sexual maturity of males and females of this species is not known but it is thought to be similar to other rhinos (35-40 years in the wild).

Habitat- The Sumatran rhinoceros inhabits mountain moss forest and tropical forests in hilly areas near to water sources and is dependent on salt licks.  This species occurs mostly in primary forest in protected areas and exhibits seasonal movements – moving uphill during seasonal flooding and wondering into secondary unprotected forest in search of water during the dry season.

Threats

The primary threat to this species (as with other rhinoceros species) is poaching for its horn to meet demands for its use in traditional Chinese medicine and for ornamental purposes.  As well as this, loss of habitat, in addition to increasing the threat of poaching has pushed the last remaining animals into small and separated populations.  This brings a considerable risk of inbreeding depression (the reduced survival probability of a population as a direct result of related individuals breeding) and reduces the viability of the remaining populations – breeding activity is not common, reproduction is not always successful and males and females don’t often come into contact in the wild.  Due to the large uncertainty around the biology of this species captive propagation programmes have worryingly so far brought very limited.

Conservation

Since 1975 the Sumatran rhinoceros has been on the CITES appendix 1 list and is protected legally in all its current range states. To stop this umbrella and flagship species going extinct, work to conserve the Sumatran rhinoceros is centred on both preventing poaching directly (through the implementation of Rhino Protection Units, RPU’s) and indirectly (reducing the demand for rhinoceros horn). Additionally the development of breeding centres to build upon recent advances of successful capture breeding techniques have offered hope for the Sumatran rhinoceros – two successful births occurred in Cincinnati Zoo with one individual being transferred back to a breeding centre in Sumatra.  Further survey work is required to determine the status of any remaining possible populations such as in Myanmar.

Sam Morton – AWF Mammalian researcher