The Megaherbivores
The rhinos along with elephants, hippos, and giraffes constitute an interesting ecological group of animals that are called the Megaherbivores; animals whose body mass exceeds 1000 kgs and feeds on terrestrial plants. In many ways, these species are just the remnant of a much larger community of massive animals that used to dominate the landscape over many continents. During the Mesozoic (65-200 million years ago) the megaherbivores were represented by a remarkable diversity of dinosaurs and then during the Pleistocene (2.5 million to 12,000 years ago) many of the ecosystems had a wide range of strange-looking mammalian megaherbivores like mastodons, giant sloths, and woolly mammoths.
Herbivores are in an arms race with their predators and to avoid being eaten they must either be faster, more agile and more astute than the predators or, they must grow to a size where they can defend themselves. Megaherbivores have taken the latter approach, sucking as much energy and nutrients as they can from plants and growing so large that predators can only bring them down when the adults are injured. To grow to such a size, these megaherbivores must have a slow life history, taking many years to obtain the energy to become massive, armed with a good thick skin and weapons to defend themselves with like tusks and horns. This slow life history entails long generation times with delayed maturity and few young each year which also means populations can’t recover fast after a catastrophe or period of heavy hunting, and constant high mortality drives their population towards extinction. Indeed, the dominant explanation for the demise of the megaherbivores at the end of the Pleistocene was the combined effects of a change in climate with human over-exploitation through hunting. Not too different from the situation our remaining megaherbivores are currently facing.
Excessive and illegal hunting of elephants and rhinos is the major threat faced by the megaherbivores. Initially the hunters were primarily after the large quantities of meat but, this is not the case today, it is now mostly for their tusks and horns which are used in both eastern medicine and are considered signals of wealth. These megaherbivores consume large quantities of vegetation and are often destructive, so are hardly compatible with modern agricultural practices. As such they are limited to the remaining, and often fragmented, wildlands and protected areas of the world. Even in protected areas they are still persecuted by illegal hunting for ivory and horns. We have explored this in previous issues where we have examined both Indian and African elephants, the giraffes and now turn our attention to the Greater One-horned, or Indian Rhinoceros (Rhinoceros unicornis) which have shown a good recovery of numbers through protection and transloaction.
The recovery of the Indian Rhino
The Indian rhino was persecuted for many years. By the end of the 19th century, the population had been decimated through excessive trophy hunting and by 1980 there were only 12 rhinos left in Kaziranga, an important national park in Assam, that should hold the focal population. Since then, the recovery of this species has been one of the great success stories of Indian conservation and it is good to see and celebrate such successes. The Indian rhino was brought back from the very brink of extinction through action by the Indian government in concert with the state of Assam so that now the IUCN estimates there to be about 3588 individuals in the wild. By 2012, more than 96% of the Indian rhinos were in Assam and the species had been eliminated from Bhutan, Bangladesh, and Pakistan. In contrast, the Indian population is now burgeoning with good populations not only in Assam but also in Utter Pradesh, West Bengal and across the border in Nepal. They inhabit the alluvial flood plains in the foothills of the Himalayas, often spending large amounts of time in the tall grasslands along the valley bottoms. This deep and difficult habitat offers protection from attack by tigers, so rhinos have a competitive advantage over other herbivore species.
Translocation to spread the extinction risk:
Megaherbivore numbers can recover from heavy poaching if the poaching pressure is eliminated totally, and the habitat is in a good state with plenty of food and free from disease. However, when the habitat is fragmented, the rhinos can’t disperse to the isolated islands of habitat and so we need to give them a helping hand to translocate them to the new sites. Occasionally translocations are also needed when small, isolated populations have lost their genetic diversity and the animals need new blood to improve genetic diversity and prevent inbreeding depression. I can’t stress enough how important it is to ensure that the limiting factors have been removed from the area before the animals are translocated otherwise you are just feeding the precious animals to a mortality factor. With some other species, like Bighorn sheep, we have seen tragedy where the animals are reintroduced into areas where the habitat is not sufficient or the pressure from disease causes mortality.
With the recovery of the Indian rhino population, the IUCN downgraded their status from Endangered to Vulnerable in 2008. The real threat to them now is habitat loss and fragmentation, with more than 70% of the current population in Kaziranga. This makes the whole species vulnerable to a catastrophic event such as a fire or a disease outbreak that could devastate the population. For example, in 2020 there was an outbreak of anthrax in Jaldapara National Park that killed at least 5 female rhinos out of a population of about 204 and this could have been much worse, so it is important to have multiple populations to spread the risk and reduce the likelihood of extinction.
There are several areas where there used to be healthy rhino populations on the border between Assam and Bhutan, but the populations have been wiped out by human persecution, either by poaching or during civil conflict. The areas are good habitat and simply need rhinos and so in 2005 the Indian government and the state of Assam launched the Indian Rhino Vision 2020 program with the objective of increasing numbers to 3000 rhinos in Assam by the year 2020, spread over seven protected areas. Initially, they planned to translocate and reintroduce rhinos into four new protected areas, but this became possible only in Manas. As a part of this program, 18 rhinos were translocated from Pobitora Wildlife Sanctuary and Kaziranga National Park between April 2008 and March 2012. Four of the animals were calves rescued and hand reared during floods at Kaziranga. Since rhinos can be stressed by long journeys in vehicles over rough roads some rhino translocations have involved moving them by hanging the animal upside down under a helicopter and moving them quickly to remote release sites. The first three months post‐release is the most critical for rhinos to settle down in a new habitat and require careful monitoring.
One of the interesting features of rhinos is that communication between these highly solitary animals is limited. They do call and have a good sense of smell, but their eyesight is weak, and they locate the presence of other animals and discover their reproductive state by visiting fecal middens. When animals are translocated one of the big problems is that this is unknown territory with no other animals so they may just get up and move off through crops and villages looking for other rhinos. To stop this wandering behavior the translocation crew introduced middens along the edge of the reserve so the animals would visit them and think there were other animals beyond. Indeed, this did seem to work for the first two individuals released, subsequent releases then knew of the presence of the original two. Interestingly, while rhinos are solitary the released animals formed casual bonds with no aggression and spent time moving together through the new habitat.
More than 200 rhinos have been translocated through this vision program and by 2018 the Assam population had reached 2650 and the best estimate was that the final 2020 population was probably not far off the target of 3000. Reintroductions were followed up with active rhino guarding and the poaching risk has fallen dramatically. This has been so successful that the chief wildlife warden for Assam has called for a second Vision program to increase rhinos again with introductions into Laokhowa Burasapori, Panidihing, and Dibru Saikhowa National Parks, areas where poaching had previously eliminated the rhino.
Other Threats
There are a few instances where the quality of the habitat has declined through the invasion of weeds into the habitat and overgrazing by domestic animals. For example, Chitwan National Park carries the second largest population of Indian rhinos and the numbers have declined because fewer female rhinos are producing calves, and this is considered indicative of negative changes in habitat quality through weed invasion. An alternative explanation could be inbreeding depression and, while there is no evidence to support this, there are concerns in Jaldapara and Gorumara where the sex ratio is almost 4 males to 1 female and the male’s fight frequently. In such situations, the loser often tries to disperse away from the park but then they walk into neighboring agricultural areas and come into conflict with people.
Conservation action clearly requires strict anti-poaching measures and at times the use of fences to stop the rhinos from damaging crops. Many areas also require targeted programs to control invasive plants and prevent the spread of woodlands into wetlands through appropriate water management. Grazing by domestic animals must be controlled and the use of buffer areas which allows some domestic animal grazing and retention of wetlands could be helpful for the rhino population in contrast to the hard edges of the protected areas. Indeed, the rhinos are a species that need wetlands and to prevent them wandering away from the reserve into opportunities for poachers, they need to retain water and moist grasslands within the sanctuary.
