|Northern white rhino at San Diego Zoo|
(taken in 2007 - I don't know if he's still alive)
It is, incidentally, not at all clear why this animal is called the "white" rhino. Not only is it quite manifestly grey or brownish in colour, it's not even a noticeably different shade from the black rhino. There are a number of theories for the name, but no particularly strong evidence for any of them. Perhaps some of the first individuals seen happened to have been rolling in chalky soil. Or maybe egrets had been pooing on them. Perhaps it's a corruption of the Dutch word wijd (meaning "wide"), and so-named because it has a broader, flatter, snout than the "black" species. Maybe racist European colonists thought they were less fierce than the "black" species. Or maybe... well, we just don't know.
Anyway, there are two subspecies of white rhino, and this is where the complexity comes in. The southern subspecies, found across southern Africa from Namibia to Mozambique and South Africa, is the one that's doing well. We cannot say anything like the same for the northern white rhino, native to a much smaller region in central Africa in the northeast of the Democratic Republic of Congo. This is classified as "critically endangered", meaning that it could go extinct at any moment.
Back in the 1980s, the only individuals in the wild were living in Garamba National Park. However, the last time anyone checked, they couldn't find even one of them. Granted, if you want to a hide a rhino anywhere, a dense jungle is probably the best place... but even so, we are talking about the fourth largest species of land animal (after the three elephants). If there really aren't any left in the national park - and, frankly, it looks pretty likely - then the only ones left alive must be those in captivity.
And we know that that isn't very many. In fact, from a certain perspective, it may be even worse than it sounds. That's because the northern white rhino may not be a subspecies at all, but an entirely separate species (Ceratotherium cottoni) in its own right. It depends a lot on how you define a species, and it's far from uncontroversial, but, if it's true, we may have discovered that there are six living species of rhino just in time to have to reduce it down to five again.
As of 2005, only two zoos held any northern white rhinos, quite possibly representing the entire worldwide population of the animals. One was San Diego Zoo, and the other was at Dvůr Králové, in the northern Czech Republic. It was the latter that apparently held the larger population. The problem was - they weren't breeding. Obviously, even in the best zoos, animals aren't living in their natural environment, and this might not be good for their libido. The zoo wondered if there was anything in the social environment of the animals that might be causing them stress, and to this end, researchers Ivana Cinková and Vitěslav Bičík undertook a five month study of the rhino's behaviour.
Up until this point, the zoo had been keeping its northern white rhinos in two groups. One consisted of three sisters, the young daughter of one of them, and a male. Indeed, the young rhino, named Fatu, had been, in 2000, the last to be born in the zoo, her father having since died. The other group consisted of a single male and the zoo's only wild-born rhino, a female named Nesari. With nothing much going on in terms of breeding, the zoo decided to switch the males, and also to move Nesari in with the captive-born females. How would they take to each other?
The researchers sat watching the rhinos for a total of over 300 hours, meticulously recording how they reacted to each other. They classified their behaviour into three categories: friendly, playful, and agonistic. For example, every time that a rhino gently rested its head on another, lay down beside it, or even rubbed it passing, that counted as "friendly".
At this point, I should probably explain, for those unfamiliar with the word, what zoologists mean when they say "agonistic". It really sounds like it ought to be the opposite of "antagonistic", but, in fact, it's one of those weird instances in English where two words that sound as if they should be opposites are effectively synonyms - "flammable" and "inflammable" being, perhaps, a better known example. Technically, agonism is fighting something, and antagonism is fighting against something. It's pretty hard to see what the heck the difference is supposed to be there, and these days, its only zoologists who still use the former word in its original sense. (For what it's worth, biochemists use it as well, but, oddly enough, not to mean the same thing)
But, anyway, agonistic behaviour in rhinos; that would mean snarling, charging, having a serious go at one another with their horns, and that kind of thing. Playful behaviour, on the other hand, is pretending to wrestle with their horns, something that males, at least, seem to quite like doing.
The researchers noticed a distinct dominance hierarchy forming within the group, with the male being picked on the most, and ending up easily at the bottom of the pile, even below the smallest female, Fatu. This, apparently, doesn't happen in the wild, at least among females, and may have been a response to being kept in what may be a large paddock to human eyes, but is doubtless rather smaller from the perspective of a species that likes to roam free across the landscape. In terms of friendly activity, there were clear stable bonds between the mother and daughter, and between the other two sisters, leaving Nesari somewhat isolated.
The reason for including her in the first place was that there is some evidence that the presence of wild-born females makes those born in captivity more likely to mate. Indeed, this seemed to work, with the male showing clear interest in the females, despite his generally submissive behaviour towards them. He was most interested in Fatu, the youngest female, perhaps because she experienced the first oestrus of her life during the study period, and was therefore presumably undergoing the rhino equivalent of a sexual awakening.
Before she, or any of the others, could get pregnant, though, Nesari had to be moved out of the group. Much older than the other rhinos, she had begun to develop painful joints, and could not be left in the sometimes chilly outdoor paddock where the others were staying. Her absence changed everything.
Suddenly, the remaining rhinos became more aggressive towards one another, the established pattern of dominance forced into a new hierarchy. While they stopped short of true violence, they seemed warier, and less comfortable. That, in all probability, stressed them out, and that's never good for breeding - something that's a common problem in zoos. The sexual activity declined, and, even four years after the study concluded, there had still been no new rhinos born.
But then, zoos aren't the best place for rhinos, or any other animal. Don't get me wrong; we need zoos, as a safe environment to protect rare species, and a source of income for conservation work. In the case of northern white rhinos, putting them back in the wild would be even worse, because then they'd probably be shot and killed for their horns. On the other hand, if they aren't going to breed, in the end, it makes little difference to the species as a whole.
In 2009, the zoo decided to do the best that it could. Four of the rhinos, including both the surviving males, were moved to a 700 acre conservation centre in Kenya, giving them a better environment than they could hope for in the Czech Republic. They're still there today, under 24-hour armed guard.
Nesari, born in the wild around 1972, was too old and infirm to make the journey. She died at the zoo in 2011, unable to see Africa again. So far as we know, the entire worldwide population of northern white rhinos may be as low as... seven.
And they still aren't breeding.
[Photo by "Sheep81" from Wikimedia Commons]