By Melissa Wray
The Riddle Of The Rare Antelope
In Kruger National Park Ask any lowveld old-timer and they will tell you that sable antelope were once so common in the central lowveld that landowners used to regularly shoot them for meat for their staff. Now a live sable is worth R150,000 on auction, and the numbers of sable, roan and tsessebe roaming wild in the veld are so low that they are verging on local extinction. Intensive farming efforts are keeping the overall number of animals in South Africa up, but the future of these species hangs in the balance in this country. The Kruger National Park (KNP) is home to roan, sable, eland and tsessebe, but a continued downward spiral in their numbers is causing a lot of head scratching amongst scientists and park management as they try to figure out what is causing the population to shrink. In the case of roan antelope, their decline has been so dramatic that park management has protected some of the animals in a 300-hectare enclosure as part of their conservations efforts. The numbers of many of the herbivores in the park began to decline in the late 1980s, probably due to several years of below-average rainfall. With the increase in rainfall in the late 1990s, numbers of most species began to increase, but the roan, tsessebe, eland and sable numbers failed to pick up.
Taking a historical look, this did not seem to be alarming as their populations are known to have cycled over the last century, with park management expressing concerns over low sable numbers in the late 1920s and early 1970s, and then reporting increased numbers in the following decades. When the numbers of the rare antelope continued to dwindle, several linked research projects were started to try and find out more about the root cause of the decline. Much of the work has focussed on sable, as they have a relatively wide distribution in the park and are the most abundant of all the rare antelope species.
However, their numbers have fallen from 2,240 in 1986 to in the region of 300 animals at present. The exact size of the population is difficult to determine as the available census methods are not sensitive enough to give an accurate estimate for such a small population. Part of the research involved placing radio-tracking collars on the sable so that the home range of herds could be figured out and correlated with the type of grasses growing in the area. Births, deaths and herd size over time could also be found out.
After several years of frustrating fieldwork, trying to locate uncommon animals in terrain that is unfriendly to radio-tracking equipment, some facts have emerged about Kruger's sable. It is now known that the sable in Kruger live in much smaller herds than elsewhere in southern Africa, they have extremely large home ranges compared to other sable, and an exceptionally high number of adult female sable die every year. By testing fresh sable droppings, the scientists have also been able to work out that the sable seem to be suffering from some nutritional deficiencies, although the animals look fine to an observer. Taking all these points together, it seems possible that the lack of something in their diet is making the sable roam far and wide to meet their food needs, stressing the animals and increasing their risk of meeting predators.
Some of the theories that have been put forward to explain why the numbers of rare antelope in the park continue to decline relate to the park's artificial water points. In the past, when the waterholes were opened, the extra water encouraged other herbivores like zebra and buffalo to come into areas that were sable and roan strongholds. These animals were then followed by lions, who found the animals to be good pickings and started eating more of them. At the same time, the zebra and buffalo could potentially have changed the types of grass growing in the sable strongholds. Sable are known to be picky eaters, eating only certain grass species and even then only nibbling on selected parts of the plant. Zebra and buffalo are more like mowing machines, cutting a swathe through all types of grass. Just as regularly mowing a lawn keeps the weed population down, herbivorous mowing machines could have changed the composition of the grasses and taken some things off the sable's menu. Many boreholes have now been closed, but just as it is hard to pinpoint exactly what effect the extra water did have, it is now hard to tell if these changes are being reversed.
Other theories on the decline of the rare antelope involve disruptions in the historical rainfall patterns, and the effects of global warming on all weather phenomena. The fencing of the Kruger National Park may also have played a role, as there are reports of sable migrating westwards towards the Drakensberg escarpment. Whatever the reason for this migration, westward movements are now stopped by a fence erected in the 1960s. Technology is now coming to the aid of the sable researchers, and they plan on putting collars on more animals next month. The new collars will be GPS-cellphone collars, which will take a GPS reading at regular intervals and then use an SMS message to send the sable's location to a special website which the scientists have access to. Test runs of these collars have had mixed results, as in some areas where the sable occur there is no cellphone reception. An even newer technology is being considered for future use, which allows a researcher to pick up GPS coordinates from a collar using a VHF receiver, removing the need for good cellphone reception.
With the ability to take many more precise readings through the GPS-cellphone technology compared to the old radio collars, the scientists will get a better picture of exactly what types of vegetation are preferred by sable and how they respond to things like burning of the veld. Collars will also be placed on zebra and buffalo in the vicinity of the sable to see if they eat in the same areas as sable, and to see if sable are as picky about their dining companions as they are about their menu. While it will take many more researcher hours and probably a lot more head scratching to figure out what is causing the rare antelope numbers to drop, this year's good rains have given researchers hope. Recent field sightings have reported a herd of four sable cows with four new calves, a much higher birth rate than has been seen in the recent past.