By Melissa Wray
In Kruger National Park
It is estimated that there are currently 1,600 lions in the Kruger National Park, give or take 225 animals, and they are nearly all in tiptop condition. This is the result of a lion population survey carried out during the winter months of 2005 and 2006. The survey is the first to study the park's entire lion population, as previous lion counts had targeted only certain areas of Kruger.
The research, led by Dr Paul Funston from the Tshwane University of Technology and Dr Sam Ferreira from the Conservation Ecology Research Unit at the University of Pretoria, saw Tshwane students Andrei Snyman and Hennie de Beer spending many nights sitting inside a steel cage on the back of a bakkie waiting for lions to arrive at loudspeakers broadcasting the distress calls of a buffalo calf.
This method of attracting lions to calling stations using distress calls is fairly standard for estimating lion numbers in an area, but this latest Kruger survey incorporated a new twist on the old technique. When the lions arrived at the calling station, the students aimed both a digital camera and a laser range finder at the lions. With these two tools, the lions' ages could be estimated based on their shoulder heights.
By measuring a lion's shoulder height in pixels in the photograph and knowing the distance the lion was from the photographer using the laser range finder's readings, the lion's true height (and age) could be determined. This allowed the researchers to not only count the number of lions in Kruger, but also to group the lions into age classes. This can give an estimate of the lion population growth rate, fertility, and other information.
Previous estimates of the lion population in Kruger have largely been based on work done by Dr Butch Smuts, who made a total count of Kruger's lions in the central region. Extrapolating from Smuts' count and other data, a frequently quoted estimate of lion numbers in Kruger has been about 2,000 animals. Prior to beginning their survey, Funston and Ferreira estimated that Kruger would have about 1,700 to 2,200 lions.
This estimate was based on educated guesses about lion densities in different zones of the park, depending on the rainfall and underlying rock types. Both rainfall and the soils produced by different rock types affect the vegetation in an area, which affects the herbivore numbers, which is related to the number of lions.
During the survey 422 lions visited 229 calling stations scattered throughout the park, and a further 273 lions were spotted by the researchers while going about their work. As the researchers did not attempt to count every single lion in the park, but used a sampling method, their final estimate of the size of the lion population in Kruger is given within standard confidence limits used by scientists. From the data, the survey indicated that there are currently 1600 ± 225 lions in Kruger (95 percent confidence limits of 1158 to 2042).
From the statistics gathered, it is clear that the researchers' early estimates of 12-15 lions/100km2 in the southern basalts and 7-8 lions/100km2 in the northern basalts were on target. However, it seems that Kruger's granite-based landscapes may support fewer lions than previously expected, as the number of lions found in these areas was just slightly under the expected 5-6 lions/100km2 in the north and 10-12 lions/100km2 in the south.
Funston comments "in the north (north of the Olifants River) and far south (south of the Sabie) lions have never before been thoroughly surveyed resulting in us having to guess/extrapolate from other areas" and that this would have contributed to the slight "over-guess".
The lions that visited the calling stations were also scored for body condition on a scale of one to five. A lion scores a five if it looks healthy with lots of muscle mass and tone; a four if it is slightly off peak condition; a three if it is a bit thin and has some major bones starting to show through; a two if it has not eaten in weeks and a one if it is on the verge of death.
Funston says, "Over 98 percent of the lions observed during the survey were either in good or very good physical condition." The average condition score of the lions in the far south was 4.9, in the central area it was 4.6 and in the far north it was 4.3.
With all the data gathered during the survey, the researchers can compare their findings with the 1970s findings of Butch Smuts, who studied the lion population in the central district of the park. Funston comments, "At that time the park was experiencing a severe drought, and artificial waterpoints had just been provided for the game.
Combined these are believed to have resulted in the lion population increasing substantially. The count of 708 lions in the central district in the early 1970s, however, compares quite closely with our current estimate of 670 lions in the same area."
"When Dr Smuts did his total count, he also determined the sex and age ratio of the population, data that is important in determining the reproductive rate and structure of the population. Here there were remarkable similarities between the current and the earlier study, with 53.3 percent and 52.3 percent of the population being comprised of adults then and now respectively. Similarly the subadults comprised 17.1 percent of the population when surveyed by Smuts and 18.7 percent during this survey. The same pattern was also evident for cubs."
With many people concerned about the effects that bovine tuberculosis (BTB) may be having on Kruger's lions, with several lions being euthanased over the last few years after being found in an emaciated condition as a result of the disease, Dr Funston comments, "At this stage we detect no population effects of BTB disease in the Kruger lion population in terms of its populations' size and structure (sex and age ratios) with both being almost identical to surveys done in the central district of the park in the early 1970s before BTB is believed to have been present."
However, Kruger's state veterinarian Dr Roy Bengis cautions that, "Any impact that may be seen in lions will possibly only be apparent when the BTB prevalence in buffalo and other prey species reaches the same levels as in the south."
The survey has not only revealed insights into Kruger's lion population, but also into that of other carnivores. More than 400 spotted hyenas were seen during the survey, along with more than 60 leopards. Cheetahs, wild dogs and black-backed and side-striped jackals also turned up to investigate the broadcasted sounds of the distressed buffalo calf. While the appearance of a carnivore looking for an easy meal is not that surprising, hippo and elephant also paid visits to the calling stations.
Looking back over the nights in the field, Funston says, "While many amazing and fascinating animal interactions were observed during the survey, including a pride of lions unfortunately killing an African wild dog near Crocodile Bridge, the team were most amazed by the arrival of a stray domestic dog at a calling station near Nwanedzi.
The dog came yapping out of the night chasing off some spotted hyenas that were lurking around. However, the arrival of three subadult lions seemed to seal the fate of the dog, especially when the young male lion decided to get hold of it. A determined chase ensued with the plucky little dog weaving and turning itself away from the lion.
When the lion eventually got up to it the dog rolled around, sneered, and growled at the lion, who quite taken aback decided discretion is the better part of valour leaving the little mutt to fight on another day." "This observation is, however, concerning as domestic dogs around conservation areas can be major agents of disease transmission into wild carnivore populations."
The many cold and dark hours spent by the students on the back of the bakkie armed with camera and laser range finder will soon be translated into scientific papers detailing Kruger's lion population. They will also be used in conjunction with other data to gain more insight into how lion densities are affected by rainfall, habitat type and herbivore densities in Kruger.
Predators appearing at the calling stations during the survey. Figures courtesy Dr Paul Funston, unpublished preliminary data.
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