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Thread: Sundarbans: Counting cats: Position update

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    Default Sundarbans: Counting cats: Position update

    November 1, 2015.
    Kolkata Xtra!
    Weekend Focus
    -Krishnendu Mukherjee

    Summary with some Excerpts:

    This almost full page article titled 'Counting Cats' commences with an immaculate image of a Tiger walking through an opening with mangroves of the Sunderbans in the background and image of one of the pair of lenses fitted on a tree at a height which would not get inundated during high tide.
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    "The image illustrates how a camera trap works. Behind the tiger is one of a pair of lenses that make up a camera trap. Whenever an animal passes between the pair of lenses, each lens takes a shot.

    Digital eyes keep watch on more than 2500 sq km of forest land in the Sunderbans. Thanks to them, we know the mangroves is home to at least 103 Tigers. But there is more to counting tigers than just taking pictures. Krishnendu Mukherjee decodes the technology that helps enumerate and identify the elusive swamp tiger.

    It was a close shave, wildlife biologist Ratul Saha still feels a chill run down his spine whenever he recounts it. In 2012, Rahul and a team of researchers were installing a remote camera in the dense vegetation of the Sunderbans, hoping to capture images of a tiger. Six minutes after the team left, the camera clicked the first still of a big cat. "It means the tiger was very near us, possibly even watching us, even as we were fixing the camera," the researcher says.

    "But a camera trap," he adds "is the most reliable gadget for counting and photographing big cats in the swamp." That's because both the Sunderbans itself and the tigers that live there are very, very different. The mangrove forest -- by virtue of its topography -- poses unique challenges to a scientists. And the tigers are also more elusive than their counterparts elsewhere.

    There was no reliable estimation of tiger number in the Sunderbans until 2012, when WWF-India's Sunderbans chapter took up the project to carry out a camera-trap survey in the mangroves. The next year, it declared the presence of a minimum of 103 tigers -- a number backed by State's forest department. The current count (for 2014) has been finished and the data has been sent to Dehradun-based Wild Life Institute of India (WWI).

    Spy in the Swamp:

    Dividing the forest into almost almost 600 grids, each spread over a 4 sq km area, the biologists laid camera trap stations where tiger signs were found. Since 2012, WWF has covered 2351 sq km of the forest under this drive. But how do the camera traps work? In essence, it's an automated digital device that's LAID IN PAIRS. It takes a photo whenever an animal triggers the sensor BY COMING BETWEEN THE TRANSMITTER AND THE RECEPTOR. " The cameras are left in the forest for 30-40 days; only the memory cards are replaced after 15 days of installation," informs a member of Ratul's team.

    Spot the Difference:

    Identifying a tiger is n't an easy job even though each has a unique stripe pattern. It's a problem of plenty, say the WWF researchers. "So far our camera traps have taken 1000 pictures and videos of tigers. And identifying 103 unique individuals from them was very difficult," says Ratul,, as he recalls the long shifts and sleepless nights during summers of 2013 and 2014.

    According to him, a tiger does not get a permanent ID unless both its flanks are photographed. "Images of both flanks help us identify individuals faster and accurately.," Ratul explains.
    So, what happens to those tigers who have only one flank clicked?

    "The stripe patterns on each flank of a tiger are different from the other. If we have 5 left flank pictures and 10 right flank images, we ignore the flank with least pictures, and take into account the side which has the most. That reduces the chances of repetition," says Ratul.

    45206 number of total stills and videos (all Animals) from the cameras have been taken which includes presence of Golden Jackals also. The camera traps are laid near sweet water ponds, places where there are signs of tigers and prey animals and areas free from human disturbance.

    Best season for installing cameras is between October and February. Mixture of rotten eggs and meat is pasted on trees at the camera locations. Distance between 2 cameras is kept at about 15-20 ft. In the Sunderbans, the trap cameras are usually withdrawn after 30 to 40 days. But the memory chips of the cameras need to be replaced after 15 days of installation.
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    Let us hope that WII will validate the presence of more number of tigers in the Sundarbans during 2014 count published in the article.


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    Good to know the camera trap method is used so well in Sunderbans for tiger census. This initiative of WWF will surely help in conservation of not only Tigers but also other rare species in Sunderbans. Thanks for sharing the detailed information.

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