Current
estimates of the number of cheetahs in the wild are ‘guesswork’, say the
authors of a new study which finds that the population in the cheetah
stronghold of Maasai Mara, Kenya, is lower than previously thought.
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) puts the figure at 6,600 – mainly in eastern and southern Africa – amid
fears that the fastest land mammal is racing to 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.
Lead
author Dr Femke Broekhuis, Project Director of the Mara Cheetah Project and a
post-doctoral researcher at the Wildlife Conservation Research Unit (WildCRU),
Department of Zoology, University of Oxford, said: ‘The truth is that estimates
of cheetah numbers are only best guesses, because cheetahs are a lot harder to
count accurately than one might think. They naturally occur at low densities
and move large distances, making them difficult to find.
‘Whatever
the exact number, we do know that they are extinct in 20 countries and occupy
only 17% of their historical range. We also know the major threats facing
cheetahs: habitat loss, human-wildlife conflict, depleting prey and the illegal
pet trade.
‘What
we have lacked until now is a way to assess whether or not conservation efforts
are effective.’
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 to estimate
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.
The
researchers also identified clear cheetah ‘hotspots’ within the Maasai Mara.
The next step is to determine how the distribution of these high-density areas
is correlated with environmental variables such as habitat, prey, predators, or
anthropogenic factors including livestock grazing.
The
results of this study will allow threats and conservation efforts to be
quantified and monitored in the future.
Dr
Broekhuis said: ‘In order to determine the impact that threats and conservation
efforts are having on the cheetah population, it is necessary to rigorously
monitor their numbers over time. Our results are therefore important, as they
provide the baseline data needed to accomplish this.
‘The
relevance of this study goes beyond cheetahs in the Maasai Mara. This is the
first time that this robust method has been used to estimate cheetah densities,
and it is a method that can be applied to other areas and other charismatic
species such as lions or even elephants.’
Co-author
Dr 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.
‘These
measures provide crucial insights about big cat ecology that aids their
conservation. For example, India has been considering the reintroduction of the
African cheetah. Even in a prey-rich area like the Maasai Mara, the density of
cheetahs is low, suggesting that the resource requirements for these cats are
perhaps much larger than would be available currently in the Indian
subcontinent.’
The
study’s authors say there is an urgent need to rigorously assess the population
size of cheetahs in all the remaining strongholds, using advanced methods such
as this one. They also suggest that relying merely on best guesses of cheetah
numbers at regional levels can seriously mislead cheetah conservation efforts
on the ground.
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