Till 1973, the lion was the national animal of India. In April 1973, Project Tiger was started to step up tiger conservation efforts and the tiger was declared as the national animal. At that time, the number of tigers in the wild stood at 1,827. There was then a rise in the numbers and in 2002 the number of tigers in the country was estimated to be over 3,500. In 2008, a report by the National Tiger Conservation Authority put the number of tigers to only 1,411 which also cast a doubt over the accuracy of the numbers reported in 2002. However, since then the number of tigers have gone up again and in 2014 the number stood at 2,226 which showed that conservation efforts were paying off.
Keeping a count of tigers in the wild or a tiger census is thus an important aspect of tiger conservation. But how are tigers counted in the wild? Let us look at the most common methods.
Pug mark method: This was invented in 1966 by Indian forester SR Choudhary. Like finger prints, each tiger has a distinct pug mark. By getting an idea of the number of pug marks in an area, the number of tigers can be estimated. So, if there are 20 distinct pug marks, there must be a minimum of 20 tigers in that area. In this method, personnel put Pug Impression Pads (PIPs) in paths tigers are most likely to use. The pug mark method is the simplest and cheapest way to count tigers and often involves a lot of local volunteers. Experts can study pug marks and know the age and sex of the tiger. However, this method is not very accurate as one cannot be sure that all tigers have left their pug marks.
Poop method: In this method, poop samples or droppings of tigers in an area are collected and then DNA sampling helps identify an individual animal and further to count the number of tigers in the area. Earlier DNA sampling was done by collecting blood samples from tigers, but collecting poop samples is easier and non-invasive. However, one cannot be sure if one has collected all the tiger droppings in an area. So this process is repeated at short intervals to arrive at a more accurate number.
Radio collar method: Here a tiger is captured, fitted with a radio collar or a transmitter and released back into the wild. This collar releases radio signals which are picked up by receiving device, which can either be a handheld device or a computer. This way one can keep track of the tiger movements and whereabouts and keep a count. This method involves tranquilising and capturing the animal, which can be harmful to the animal in some cases. Also, sometimes radio collars get detached from tigers. Further in areas like Sunderbans, this is not a feasible idea as these devices do not function when exposed to salt water.
Camera trapping method: This method uses infra-red cameras or cameras that can record even at night to record images of tigers. These cameras are placed strategically in areas where tigers are present and are triggered either by motion or by heat of the animal. The recorded images from all the cameras are analysed properly, because sometimes the same tiger may have been filmed twice and researchers arrive at a count. However, like the pug mark method, this is not accurate as all the tigers in a certain area might not have been filmed. Further this method is difficult to apply in salt water areas as that damages the cameras.
Tiger counting is done involving one or more of the above methods. Since tigers reside and hunt in a certain area, such estimates are cross checked by the number of preys hunted by tigers in that area. Also most of these tests are conducted in summer as tigers are more likely to come to waterholes to drink water at that time, thus making it easier to implement these methods.
Accurate counting of tigers is essential to figure out the effectiveness of tiger conservation programs and step up future conservation efforts based on the learning.