Kruger National Park's lion population faces an uncertain future - or does it?
That was the question facing scientists at a Lion Bovine Tuberculosis Disease Risk Assessment Workshop held in 2009.
The collection of scientists from around the globe found answering the question of how Kruger's lion (Panthera leo) population would respond to the increasing prevalence of bovine tuberculosis (bTB) in the Parks' buffalo herds more challenging than most had expected.
This was despite having sophisticated mathematical models designed to answer such questions and the results of a number of research projects conducted on the lions. The problem was that predictive models are only as good as the information they are using.
The reliability of the model and validity of the results it provides are highly dependant on the both the quantity of data channelled into the model, but more importantly the quality of that data. To model the population effect of a specific disease like bovine tuberculosis, a detailed understanding of both the disease transmission rate and the demographic response to the disease in lions is required. Unfortunately, there are big gaps in current knowledge when it comes to both these aspects of the disease.
Undeterred by the extent of information required, SANParks has commissioned one of the largest investigative studies of its type, to gather the information needed to model the effect of bTB on Kruger's lion population. It is a multi-faceted research programme, dependant on expertise from across a number of SANParks departments including Scientific Services, Veterinary Wildlife Services, as well as researchers from the University of Pretoria and Onderstepoort Veterinary Faculty.
Dr Sam Ferreira, SANParks' large mammal ecologist, heads the programme. He explains that the aim of this project is to collect data which will try and fill the current gaps in knowledge. These gaps include understanding both the vertical and horizontal transmission rates of the disease.
Vertically transmission is via predation, with buffalo being the primary hosts for bTB in the park and one of the lions' favourite food sources. The lions catch bTB from feeding on diseased buffalo. There is a concern that male lions could be particularly susceptible, as they often get first choice at a kill and will frequently select the most disease-ridden parts, including the lungs.
Horizontal transmission is intra-species transmission from lion to lion. Lions are social animals, feeding, sleeping, playing, and hunting in prides. Due to their social nature, lions tend to be particularly susceptible to horizontal intra-pride transmission, as bTB is an airborne disease and lions breathe over one another constantly, especially around a kill.
Another gap in current knowledge is the demographic response of lions to bTB. Little is known about how bTB affects the birth intervals, fecundity, cub survival rates, life spans and pride takeovers in lions.
Sam's programme aims to test all this, by collecting detailed information from 30 prides over a six-year timeframe. Kruger will be split into three distinct regions - southern, central and northern - and ten prides will be studied in each. These regions will differ in the amount of prey available and prevalence of bTB, both of which can influence the demographic response in the lions.
However, no distinction will be made between the different zones, granite and basalt, within each region. Re-sampling of each pride will happen every two years, although every two months, researchers will spend three days and nights with the pride, using radio collars to track their every move and recording the behaviours they witness.
Before this can happen, the 30 prides have to be caught so that collars can be attached and initial samples taken. Collaring 30 prides carries a large cost, both financially and logistically. The programme has therefore been split into three smaller projects, according to the different regions, to make it more feasible.
Currently collaring and sampling of lions in the southern region has started, with a team from SANParks going out on a week of night captures. Using a fresh carcass and a calling station the team hopes to draw in a pride from the vicinity. Audio calls are particularly important, and a lot of work is going into what sounds work best.
Traditionally, buffalo distress calls and the sounds of hyenas noisily celebrating a kill have been used. Both bring in lions, however, the lion's response differs dramatically. Hyena calls will bring lions in from a great distance however it will tend to be male lions looking for a fight, whereas the buffalo distress call tends to bring whole prides in, but from a lesser distance.
Small factors like these need to be considered when setting up call-ups given that SANParks wish to attract prides and not only males. When the lions have been called in, vets from Veterinary Wildlife Services dart as many of the individuals of a pride as possible.
Several tests commence once lions have been retrieved at the capture site with assistance from the Operations Unit. Currently there is no solid test to diagnose bTB in lions, so two associated projects under the auspices of the KNP Veterinary Unit aim to evaluate methods of testing in the hope of finding a reliable, standardised test for bTB.
Alongside testing for bTB, screening for a number of other feline diseases will be carried out, including testing for feline aids (FIV). A pioneering study by Dr Dewald Keet stimulated a lot of the discussion surrounding bTB in Kruger's lion population and identified a potential correlation between the effects of bTB and lions that have also have FIV. Dr Danny Govender from Scientific Services screens captured lions which hopefully will shed some light on how the various feline diseases affect the survival and reproduction of lions either on their own, or in combination.
As well as the physiological studies, a behaviour study will also be undertaken. From each pride selected females will be collared. These will hopefully provide scientists with a lot of the data they are currently missing. Researchers will follow the prides and will document everything from interactions on a kill to litter sizes. These observations will provide the team with the life history data for bTB prides they are currently lacking as well as giving them much better insights into disease transfer rates.
One of the aspects of lion capture which makes it such a drawn out process, is waiting for the lions to wake up after being anaesthetised. Male lions from different coalitions are notoriously hostile to resident pride males, so the team have to stay with the lions until the effect of the drugs has totally worn off, otherwise other prides might come in and take advantage of the sleeping or drowsy lions.
The team is addressing this by looking at new drug combinations. Dr Peter Buss, from Veterinary Wildlife Services, is also involved in this project. He is looking at refining a drugs trial he initiated in October 2009, which would replace zoletil (the traditional drug used for darting lions) with a combination of drugs that includes butorphanol, medetomidine and midazolam.
This new combination of drugs will enable the vets to reverse the drug effects, when and if required. So the lions can be quickly back on their feet after all the sampling has been completed, reducing the waiting time dramatically. It also gives the vets the option of using the reversal drugs if the lions experience any troubles under the anaesthetic, an option previously not available to them, lessening the risks associated with anaesthetising lions.
The project is in the very early stages. Lion capture in the southern region of Kruger started in early March this year. 10 females from 10 prides have been successfully collared and a total of 51 lions caught and tested. It won't be until 2011 that all 30 prides will have been selected and even then that is just the beginning of an intensive six years of data collection.
However, these initial efforts by the SANParks team, their colleagues from various academic institutes and the sponsors, who have made all this research possible, will result in a significant difference in six years time.
Then when asked whether "Kruger Nationals Park's lion population faces an uncertain future due to bTB" the scientists and managers of Kruger National Park will be able to have a better understanding of what influences lion survival in the Kruger and how significantly TB is playing a role in lion survival.
By Katy Johnson