|
after puberty there is a marked acceleration in the growth - the post-pubertal growth spurt - leading to great differences in the size of mature males and females. Hence adult bulls are twice as heavy adult cows and taller. Distribution and number
About 6,000 years ago, the range of the Asian elephant extended from the Euphrates-Tigris river systems in the west to China in the east. Today it is distributed discontinuously in India, Nepal, Bhutan, Bangladesh, Myanmar, Thailand, Peninsular Malaysia, Sabah (Malaysian part of Borneo), Kalimantan (Indonesian part of Borneo), Cambodia, Laos, Vietnam, South-eastern China, and the islands of Sumatra (Indonesia) and Sri Lanka. A feral population occurs on some of the Andaman Islands (India). Modern DNA studies reveal that Borneo’s elephants are genetically distinct and that they may have diverged up to 30,000 years ago from their closest relatives in Peninsular Malaysia. There were nearly 12,000 elephants in Sri Lanka at the turn of the 19th century, but today total is estimated to be about 4,200 (or roughly 10% of the global population of Asian elephant). The decline in numbers by almost 65% is largely due to the expansion of agriculture to sustain an ever-growing human population. The present human-elephant ratio in Sri Lanka is 4,760:1. IUCN lists the Asian elephant as an endangered species, while CITES places it in Appendix 1.
Ecology
Elephants occur in discrete populations. The basic population unit is the herd, consisting of an integrated group of closely related elephant of all classes excluding adult males. Elephant society is multi-layered, ranging from the mother-calf or nursery unit, through the family unit, the 'kin' or bond group (2-5 family units which associate freely), the clan (a number of family units and bond groups in an area), the subpopulation (a number of clans using a particular part of the range), to the whole population. Females remain in the cow herds of their birth, which are essentially a matriarchy being led and co-ordinated by the oldest reproducing cow, who is probably the mother, aunt or grand-mother to most of the females. Larger herds with older, more experienced matriarchs are more successful in exploiting high quality habitats, and thus ensure better survival of young, than smaller herds with younger, less experienced cows. When a herd splits up into family units and is reconstituted, the reunion is usually a highly vocalised, emotional greeting ceremony, during which members will often touch each others' mouths, faces or genitals, and rub each others' heads or bodies to reaffirm their links and relationships. Herd size ranges from 8-20 animals. The matriarch’s presence is crucial to the survival of the herd, for she is the repository of knowledge.
While females become sexually active between 9-12 years, males reach sexual maturity between 12-15 years at which time they are forced out of their natal herds to prevent inbreeding. Adult bulls live alone, or in small temporary groups ("bull herds") with weak social bonds. The composition of the bull groups changes both in space and time. Bull elephants exhibit the phenomenon of musth, similar to the rut in deer, during which the amount of testosterone in blood soars to much higher levels than usual. Although the secretions of the temporal glands are associated with heightened sexual activity and aggressiveness among bulls, males can successfully mate with females even in the absence of musth. Bulls in musth constantly dribble strong-smelling urine, shake their heads and wave their ears in order to waft the temporal gland scent to other bulls or to receptive cows. Musth even affects conversation between males and females. Elephants are extraordinarily vocal animals which communicate on infrasound (14-24 Hz) audible to other elephants but not to us. Bulls are usually the strong, silent type probably because unlike cows, they haven’t got large vocabularies. Females are in heat only for a short time, and they announce their brief receptive periods in advance through chemical, auditory and behavioural signals increasing the likelihood that multiple males will be available as mates to choose from, and they prefer older males. Often it is the 40-50 year old bulls which father most calves. Sexual maturity alone does not guarantee access to estrus females; young bulls have to be socially mature as well. This would take an additional 8-10 years, which is too long a wait even for an elephant with sex on its mind. It is a case of SINBAD: Single Income, No Babe, Absolutely Desperate! Females have a long reproductive period, from about 12 to 60 years, during which time they could produce as many as 12 calves. From the moment a calf is born, after a gestation period of nearly two years, it becomes the centre of attention of the herd, fussed and fondled by the herd members. Juvenile female helpers known as 'allomothers' are important in the rearing of calves. A calf that is born into a large family with several allomothers has a better chance of surviving than one born into a small family with few or no allomothers. Calves suckle on demand, but male calves are known to demand more milk than female calves, and so become bigger even by the time they are juveniles.
Given their large size and intemperate appetite, elephants in the wild need to consume huge quantities of food per day. Hence they are less discriminating than other herbivores in what they eat. They browse and graze on a variety of plants. But the proportions vary both in time and space. During dry season, 70% of an elephant’s diet is browse, while in wet season, grasses make up about 55%. Elephants may feed on more than 60 species belonging to 30 families. Nevertheless, just a few species may account for an elephant's total intake. Bamboo and sugarcane among grasses, and fruits of Tamarind (Tamarindus indica), Wood apple (Limonia acidissima) and Palmyrah palm are preferred. Elephants in Sri Lanka are also known to feed on fallen, over-ripe and already fermenting fruits for their alcoholic content, after which they often move about and stagger in a disorganized manner like their countrymen under similar situations. Elephants may also include bark in their diet in order to provide roughage. As the elephant does not have a rumen, cellulose is digested in the large caecum and the colon, with the help of symbiotic microorganisms. The passage of food through the gut is fast, and the ingested food is only partially digested, with between 44-48% ending up as waste. Elephants may spend 17-19 hrs a day feeding, during which they may consume up to 150 kg of wet weight. They also defecate about 16 times a day, producing about 100 kg of dung. The recycling of dung is very important for the health of the ecosystem. Dung also helps disperse germinating seeds.
Elephants in Sri Lanka do not make long distance migrations as their cousins do in Africa. They tend to restrict their movements to a particular segment of their habitat, which is referred to as their home range. While home ranges of individual African bush elephants (Loxodonta africana) may stretch across thousands of km2, those in Asia tend to be rather small, and in Sri Lanka, smaller still. Radio-telemetric studies indicate a home range size of 50-150 km2 for herds, and 380 km2 for solitary bulls.
Conservation
Sri Lanka has already lost almost 80% of its original forest cover. The elephant is running out of space among 20 million people living in the island. In 1870 when the human population was 2.4 million, the land:man ratio was 2.7 ha. Today, the land:man ratio is 0.35 ha but could be as low as 0.15 if chena, pasture and patanas are excluded. Over much of the island, there is no longer room for elephants to move about and adjust their densities to changing vegetation patterns. Almost 70% of the elephant range lies outside the system of protected areas. Changes in land-use patterns are resulting in a continuous contraction of habitat available to the elephant. When elephants lose their range, they die. Sri Lanka has set aside 8,580 km2 of land (or 13% of the total area) for nature protection. But most of the conservation areas are small with low area:perimeter ratios and farmers living along the periphery are vulnerable to elephant depredations.
Given that for every wild elephant in Sri Lanka there are 4,760 people, it is inevitable that conflict between man and elephant would be intense. Between 1950 and 1970, a total of 1,163 elephants died in the wild, while between 1990 and 2001, a further 1,369 perished. Elephants are not being killed in Sri Lanka for ivory, since tuskers are rare; they are not being killed for meat, since no one eats elephant steak; they are not being killed for leather, since the hide has no commercial value. Instead elephants are being destroyed simply because they interfere with agriculture. The long-term future of elephants outside the protected areas is inextricably linked to the tolerance of man. The human-elephant conflict has replaced poaching as the biggest conservation issue in Sri Lanka. The conflict is real and it is leading in just one direction: the destruction and eventual elimination of elephants from agricultural areas, unless innovative measures are adopted to address the concerns of the farmers. The management of human-elephant conflict has to be integrated into a proper land-use policy and it must also recognize the elephant as an economic asset. If local people could perceive the elephant as an economic asset instead of an agricultural pest, then they will tolerate it in their neighbourhood. Unless people value living with elephants, the slaughter will go on. Given that the human-elephant conflict is already bad today, it may become worse tomorrow. Even if we cannot eliminate the conflict altogether, we need to reduce it to tolerable levels.
The Asian elephant is often referred to as one of the world's important and charismatic
"Flagship" species. It is also an
"Umbrella" species, given that its conservation will benefit other sympatric species. The elephant is also known as a
"Keystone" species, to emphasize the vital role it plays in the structuring of natural communities. Thus, the conservation of the elephant will ensure the maintenance of biological diversity across a much larger area. Reference
to the above material from:
©
Charles
Santiapillai1, S.
Wijeyamohan2 and Rajnish
Vandercone1 (2003)
1
Department of Zoology, University of Peradeniya, Sri
Lanka
2
Department
of Biological Science, Vavuniya Campus of the University of
Jaffna,
Sri
Lanka
>> Back
to the Main Page
|
