January 12, 2015
|
Editor’s Note: “Along the Tiger’s Trail” is a series about the
efforts to monitor tigers and their prey in the Malenad landscape in
southwestern India that harbors one of the world’s largest population of
wild tigers. The series tracks on-going annual activities of the
world’s longest running research project on tiger and their prey,
implemented under the leadership of Dr. K. Ullas Karanth of the Wildlife
Conservation Society. These tales from the Indian jungles will take
you through a virtual journey into the lives and work of people
dedicated to the cause of India’s wild. For more posts in the series click here.
Counting secretive, elusive animals, such as the tiger, is a challenging task. Unlike other big cats that are easily seen in open African savannahs, tigers largely inhabit dense tropical forests. This makes tigers hard to find, and aerial surveys or vehicle-based counts become logistically infeasible and do not yield sufficient information for reliably counting them.
In the 1990s, frustrated with the inaccurate ‘pugmark’ based counting approach
widely used in India, which relies on making and comparing plasters
casts of animals’ footprints, Dr. Ullas Karanth devised an innovative
approach to solve this. He set up motion-sensitive cameras inside
forests that allowed tigers to trigger and click their own photographs.
Camera traps were not new. In India during the 1920s, British forester
F.W. Champion used cameras with tripwires to photograph tigers and
leopards in the Western Himalayan foothills—a primitive wildlife selfie
of sorts. Dr. Karanth adopted this method to identify and count tigers
scientifically.
Camera trapping is a strenuous and sometimes difficult task. It requires driving and walking through rough terrain to set up cameras, discreetly placed along forest roads and trails frequented by tigers. Once set up, cameras have to be routinely checked. Occasionally they are stolen by people or damaged by elephants. Our field season lasts between six to eight months. We set up over 700 camera trap stations covering 6,000 square-kilometers of prime tiger habitat every year in India. The outcome is over 15,000 images of tigers, leopards, dholes, elephants, deer and a suite of other secretive animals.
So how are tigers counted using photographs? Every tiger has a unique
stripe pattern that allows us to identify each individual. As with
human fingerprints, no two tigers have the same stripes. This enables us
to count the number of tigers ‘captured’ in the camera traps.
Innovative statistical modeling also allows us to estimate the
proportion of tigers missed.
Sifting through thousands of tiger photographs to match individuals based on their patterns is a monumental task! Our collection of tiger images spans two decades and we have now identified almost 800 individual tigers. As new tigers are photographed every year, it becomes increasingly difficult to match individual tigers. To make this easier we use a pattern matching software called ExtractCompare (developed by British statistician Lex Hiby). The pattern-matching algorithm extracts stripe patterns to shortlist the most closely matched tigers. Trained technicians help identify the tiger from this shortlist, if it exists in the database.
Over the last two decades, we have expanded from 15 cameras in a
single reserve to 700 cameras in seven tiger reserves across India. We
estimate tiger numbers accurately and have gained fascinating insights
into tiger ecology, behavior, survival, recruitment and dispersal in one
of the most important tiger populations in the world. As a bonus, we
now have information on a host of other rare and elusive animals such
leopards, dholes, leopard cats, civets and mongooses, making tigers the
quintessential “umbrella species” in the Western Ghats of India.
About the Author:
Right and left flanks of a tiger captured in a camera-trap.
Counting secretive, elusive animals, such as the tiger, is a challenging task. Unlike other big cats that are easily seen in open African savannahs, tigers largely inhabit dense tropical forests. This makes tigers hard to find, and aerial surveys or vehicle-based counts become logistically infeasible and do not yield sufficient information for reliably counting them.
WCS field teams set ting camera traps.
Camera trapping is a strenuous and sometimes difficult task. It requires driving and walking through rough terrain to set up cameras, discreetly placed along forest roads and trails frequented by tigers. Once set up, cameras have to be routinely checked. Occasionally they are stolen by people or damaged by elephants. Our field season lasts between six to eight months. We set up over 700 camera trap stations covering 6,000 square-kilometers of prime tiger habitat every year in India. The outcome is over 15,000 images of tigers, leopards, dholes, elephants, deer and a suite of other secretive animals.
A 3D model wireframe fit onto a tiger with ExtractCompare sof tware.
Sifting through thousands of tiger photographs to match individuals based on their patterns is a monumental task! Our collection of tiger images spans two decades and we have now identified almost 800 individual tigers. As new tigers are photographed every year, it becomes increasingly difficult to match individual tigers. To make this easier we use a pattern matching software called ExtractCompare (developed by British statistician Lex Hiby). The pattern-matching algorithm extracts stripe patterns to shortlist the most closely matched tigers. Trained technicians help identify the tiger from this shortlist, if it exists in the database.
Matching tigers' stripe patterns from camera trap images.
Arjun Srivathsa
is a Research Associate with the WCS India Program. He studies dholes,
leopards, tigers and other mammals in the Malenad landscape, and his
research interests include wildlife behaviour and ecology among others.
He was honoured with Sanctuary Asia’s Young Naturalist Award for 2014.
Dr Krithi K Karanth
has been working for wildlife conservation in India for the past 15
years. Declared a National Geograpic Society Explorer in 2012, she is
currently an Associate Conservation Scientist with WCS New York. Her
research encompasses a broad range of issues examining human dimensions
of wildlife conservation.From Scientific American
No comments:
Post a Comment