Experts from the Indian Statistical Institute and the University of Oxford have devised a new method to accurately count cheetahs after finding that recent estimates of their numbers were a “best guess”.
In the early 1900s, it was believed that around 100,000 cheetahs roamed the earth. The most recent estimate by the International Union for Conservation of Nature (IUCN) stood at 6,600 – mainly in eastern and southern Africa – amid fears that the fastest land mammal is racing towards extinction.
However, a team of scientists from the Kenya Wildlife Trust’s Mara Cheetah Project, the University of Oxford and the Indian Statistical Institute says this number is simply a best guess, given the difficulty of counting cheetahs accurately.
The researchers have now developed a new method to accurately count cheetahs, which in time will help determine the magnitude of the threats they face and assess potential conservation interventions. The study is published in the journal PLOS ONE.
During a three-month period, researchers in five vehicles extensively covered the Maasai Mara National Reserve and surrounding wildlife conservancies in search of cheetahs. The field team photographed each cheetah that was seen and identified each individual based on its unique coat pattern.
These data were then analysed using an advanced Bayesian Spatially Explicit Capture Recapture (SECR) statistical model. This technique, incorporating information such as identity and location, is more powerful than previous methods used for estimating cheetah numbers.
The study revealed an average of 1.28 adult cheetahs/100km2 in the Maasai Mara – an average total of 30 animals. This number is lower than previously thought – around half, in fact.
The ‘spatially explicit’ method used can distinguish ‘visiting’ animals from those that reside permanently within the surveyed area, avoiding potential overestimation. The researchers compare this to counting the population of Manhattan in the daytime, which would give a vastly inflated figure because of the influx of commuters from neighbouring areas.
Co-author Arjun Gopalaswamy, from the Indian Statistical Institute and the Department of Zoology at the University of Oxford, said: “The method we have used accounts for detection probability and is therefore more accurate than other methods that are currently being used to estimate cheetah numbers”.
“In addition, the modelling approach we have used allows for estimating not only abundance and density, which were of prime interest to us, but also provides vital information about adult sex ratios and sex-specific home range sizes”.