Very early Saturday morning kossack noweasels published this fine diary, detailing the news that Nesari, one of only eight northern White Rhinos in existence had died. Even without knowing that astonishingly small number of individuals, the fact that the death of an individual rhinoceros in the Czech republic was international news indicates the gravity of the plight of the northern Whites.
It seemed appropriate to devote this week's diary to the plight of rhinos in general and to discuss how their very size works against them in this modern age. I apologize for not getting this diary out at my quasi-regular sometime on Sunday evening but my preparations yesterday were interrupted by a violent thunderstorm.
Rhinos belong to the order Perissodactyla, the odd-toed ungulates. These are hoofed animals that have either 3 toes or one toe on each foot. There are only three living groups of odd-toed ungulates: the horses (including zebras), tapirs, and rhinos. None of these groups have very many living species and, with the exception of the domesticated horses and donkeys, none of the living species are particularly abundant.
The family Rhinocerotidae includes the five (possibly six) living rhinoceros species and many extinct species. Fossil rhinoceros species are known from over most of the continental land masses of Eurasia and North America and also in Africa and Central America. No fossils are known from Australia, South America, or Antarctica. Some species were considerably smaller than current forms, the smallest being dog-sized. Others include giant forms including the giraffe-like Paraceratherium which stood over 25 feet tall with its head raised and had a five foot long skull. It may be the largest ever land mammal.
The living species of rhinoceros fall into three distinct groups and include some of the most endangered mammals on earth. In some ways rhinos are poster children for how to become an endangered species. What makes them so vulnerable?
All living rhinos are large herbivores. With the possible exception of the smallest species, the Sumatran rhino, adults probably suffered little predation before encountering humans. A major cause of death in at least some species was wounds suffered in combat with other rhinos.
Baby rhinos are more vulnerable and like many other ungulates rhinos are born at a fairly large size and advanced state of development (so they can run when they are as young as possible). A consequence of this is that rhinos only have one offspring at a time and fairly infrequently.
So rhinos are large (so need a lot of space), aggressive (don't do well living near humans), slow to reproduce, and generally not fearful of predators. Not a combination of traits that does well in contact with humans. And particularly not with humans that can kill a rhino safely at a distance with a high-powered rifle. Adding to the danger, some humans have decided that rhino horn is extremely valuable either as dagger handles or medicine. Rhinos are somewhat unusual for a land animal today in that poaching is actually a bigger threat to their survival than habitat loss, especially for the African species.
Rhinos are a really good example of organisms with a Type I survivorship curve. A survivorship curve is the pattern of mortality in a species or population as individuals age. Type I organisms have few and fairly large offspring. Juveniles have low mortality and take a fairly long time to become adults. Unfortunately these characteristics mean that even under ideal circumstances the rate of population growth is fairly slow (consider what would happen if every individual offspring of a Type III species (e.g. an alligator or an oak tree) survived to adulthood - the population would grow a thousand fold every generation). So rhino populations will decline rapidly under hunting pressure and recover slowly.
Let's take a look at the status of the living rhino species.
Africa - Black and White Rhinos
Africa has traditionally been considered to have two rhino species: the White Rhino and the Black Rhino. These names are confusing as both species are the same color - gray! It is thought that the term white is corruption of the Dutch word for wide. The White Rhino can distinguished by its broad, squared off mouth and snout which is primarily used for eating grass. It contrast, the head of a Black Rhino comes to more of a point with a prehensile upper lip that allows it to grasp twigs and leaves. The African species are almost mirror images when it comes to conservation.
The White Rhino has two subspecies: Northern and Southern. These two have been historically quite separate and may not have been in contact for a million years. So some biologists consider them separate species. White Rhinos are the largest living Rhinos with large males ranging up to 3500 kilograms and the all time record animal weighing 4500 kilograms. After the Elephant species and the Common Hippopotamus, it/they is/are the largest living land mammal(s).
Southern White Rhino showing the wide mouth.
Note I am using the metric system (this is a science diary after all). A kilogram is just about 2.2 pounds so a 4500 kilogram animal is almost 10,000 pounds!
The Southern White Rhino is found in South Africa and adjacent countries. A century ago it was the rarest of rhinos with only a couple of hundred animals left. The population decline was due to hunting (then legal) both by farmers and big game hunters. Today approximately 2/3 of all rhino individuals on the planet are Southern Whites (somewhere in the vicinity of 15,000). The success of Southern White Rhino conservation is due to the resources and protection that South Africa, a relatively wealthy country has been able to provide. Also, Southern White Rhinos can be bred in captivity reasonably well in contrast to some of the other species.
The Northern White Rhino is at the other end of the spectrum. The last group of wild individuals appears to have been wiped out in the eastern Congo about five years ago, leaving a global population of only eight captive individuals at that time. The four most likely breeders have been sent to a facility in Kenya where they are being maintained in semi-natural conditions either as a pair or with a group of Southern White Rhinos. With only four individuals it is highly unlikely that a new population can be established by 'pure' breeding and so interbreeding with the Southern Whites is considered preferable to complete extinction. The remaining captive individuals (now three in number) are not considered to be likely to breed under any circumstances either due to age or behavioral issues.
The Black Rhinoceros was the most abundant rhino species on the planet with a global population estimated at 70,000 just forty years ago. It is about half the mass of the White Rhino on average with large males reaching 1600 kilograms. The black rhinoceros is known as a quick and aggressive species and is probably the most dangerous species to humans. Poaching has led to extreme declines in Black Rhinos, particularly in the northern part of it range and the global population appears to be around 4,000 individuals. There is considerable uncertainty about this number (ten years ago it was thought to be half that) largely due to this species being spread across many countries, many of which have local conditions that make an accurate census difficult. Extreme measures have been taken to protect individuals of this species including individual armed guards for Rhinos and cutting off their horns.
Black Rhino
Asia - Indian, Sumatran, and Javan Rhinos
The Asian Rhinos are not as well known as the African species. Asian species mostly live in forests and are not as easily observed and filmed. In contrast to the African species, whose population declines really started in the 19th or 20th centuries the Asian species appear to have been in decline for a long time. Their common names are also problematic as none of the species are actually restricted to the location for which they are named (and all had quite wide ranges in earlier times).
Indian Rhino and calf at the Buffalo Zoo
The Indian Rhinoceros is a very impressive animal. It is only slightly smaller than the White Rhino with some individuals achieving weights over 3000 kilograms. It has a massive stocky body and thick skin that forms great folds. The overall impression is of an animal encased in armor. Unlike the two African species individuals only have a single horn. Indian Rhinos range across northern India and southern Nepal. Two individuals have been introduced into a national park in Pakistan where the species once occurred. All individuals are now found in preserves. The global population is somewhere between 2500 and 2700 individuals and has been increasing over consistently over time for several decades. Around 70% of the global population is found in Kaziranga National Park in northern India and over half of the other individuals are in Chitwan National Park in Nepal.
The Javan Rhinoceros is the rarest species save for the Northern White and may be the rarest large mammal on earth. Once occurring through much of southeast Asia this species is now restricted to two preserves: one at the western end of the island of Java in Indonesia and another in southern Vietnam. The Vietnamese preserve is estimated to have only eight individuals and the Javan preserve between 40 and 60. No individuals exist in captivity. The extensive series of conflicts in Indochina in the 1960s and 1970s are probably a major factor in the almost complete extinction of this species in that area. The Javan rhinoceros is very similar in appearance to its close relative the Indian rhinoceros but is a smaller animal. It appears to be similar in size to Black Rhinos but there is a shortage of data.
Javan rhinos in the wild in 1930
The final species is the Sumatran Rhinoceros. This species is fairly distantly related to the all the other living rhinos Instead it is thought to be more closely related to the extinct woolly rhinos. It is easily the smallest rhino species with large individuals weighing about 800 kilograms (more in captivity) and is further distinguished by having more extensive hair than other rhinos. Unlike the other two Asian species it has two horns. In most individuals the horns are quite small, particularly in females where they may be no more than bumps. Some individuals do have longer horns. Sumatran rhinos are solitary forest dwelling animals and are only marginally better known to science than the Javan rhinoceros.
Historically this species occurred from Sumatra and Borneo up the western side of Indochina to extreme eastern India. Today six substantial populations remain, four in Sumatra, one in peninsular Malaysia, and one in eastern Sabah, a Malaysian province in northern Borneo. It is possible that a handful of individuals remain scattered elsewhere in its range, most likely in Borneo or Sumatra. Population estimates of this species are particular difficult to make because of its solitary forest-living way of life but only somewhere between 200 and 300 individuals remain in the wild. A large scale plan to breed the animals in zoos in the 1980s was not successful and is largely responsible for the decision to not attempt captive breeding with the Javan rhinoceros. Most of the individuals died and successful breeding did not occur until the past decade when a pair at the Indiana Zoo produced multiple offspring. Malaysia has kept small numbers in captivity but does not seem to have seriously pursued captive breeding. In 2004 a par of Sumatran rhinos were being kept in large enclosures within the forest at the Sepilok Orangutan sanctuary in Sabah and we were charged extra if we wished to see them.
Sumatran Rhino in forest pen in Sabah, Malaysia
It is possible, although unlikely, that one or the other (or both) of the Sumatran rhinoceros and Javan rhinoceros may persist in Burma as that country has been largely closed to outsiders for many decades.