Explained: How are tigers counted in wild?

The Centre in its recent report announced the presence of five tigers in Goa. This comes after Goa responded in the negative to the same report, saying that there are no tigers in the state.

As per the Centre, population of the big cat only seems to be growing in Goa.

The Status of Tigers-2022 report was launched by the Union Environment Ministry on Saturday. It claims that five tigers were recorded from the forests of Goa last year, a rise from three tigers recorded in the 2018 census.

Amid this state vs Centre dispute on the tiger count, let's dig in and find out how the population of these majestic big cats are calculated in the wild.

How it all began?

Counting of tigers in India began in 1973. The forest officials would use glass and butter paper to track pugmarks. Just like human fingerprints, every tiger has a unique footprint.

Forest rangers would trace the joint marks of the tiger's foot and trace it on butter paper to imprint the pugmark. They later use it to track the same tiger in future.

However, this is more difficult than it sounds. Pugmarks of a tiger differ when it's sitting, standing, running, or resting. This made the entire effort cumbersome and prone to discrepancies.

Over the years, this practice evolved and became more of a statistical method. Rangers have now switched to capture-mark-and-recapture technique. This is mainly used to estimate the tiger count based on collected samples.

According to Northern Arizona University, the key here is to capture a small number of tigers, put a harmless mark on them, and release them back into the wild. "At a later date, you catch another small group and record how many have a mark. In a small population, you are more likely to recapture marked individuals, whereas, in a large population, you are less likely. This can be expressed mathematically."

Elusive species? Not anymore. Thanks to camera traps

Form the mighty Himalayas to dense forests, tigers are as elusive as they can get. They are not just hard to count, but hard to locate as well. However, thanks to camera traps placed in the jungles by forest officials, the behaviours and movements of tigers are not a mystery anymore.

Catering to 60 per cent of the entire global tiger population, India uses these camera traps extensively in its tiger reserves. Interestingly, this technique makes India's tiger counting efforts the largest camera trapping exercise in the world.

During the tiger census of 2018-19, about 27,000 camera traps were used in India which clicked over 34 million pictures, out of which 76,651 were of tigers. This massive effort has been registered in the Guinness World Records.

Why is it important to keep tab on tiger population?

India conducts tiger census once in every four years. This helps in determining the number of tigers roaming in the wild.

The data collected via these surveys are crucial as it helps in keeping track of tiger population trends, highlighting concern areas, and sometimes, even encouraging success stories.