A camera is set inside a rugged waterproof box, which is fixed to a tree or post. This is called a camera trap because, when it senses motion, it records — or “traps” — videos and photos. Most camera traps use infra-red light to see in the dark, though some do use a flash to illuminate the area. Usually, this goes on till the battery lasts or the memory card becomes full; another hazard is a curious animal.
What it catches
A camera trap is extremely useful for documenting wildlife, like taking a tiger count. First, a tiger’s active trail is identified after fieldwork and camera traps are place on both sides so that the animal’s right and left flanks can be captured. As a bonus, other kinds of wildlife, people, even a fluttering moth or a leaf falling to the ground can trigger the camera.
Once the photos are recovered, they are shortlisted on the basis of whether both flank patterns are clearly visible. Tiger stripe patterns are unique to each individual, just like human fingerprints! While recognising individual tigers cannot be done manually, computer and pattern recognition software are a big help. Once the shortlisted patterns are entered into a database, the images are checked against what already exists. If the pattern doesn’t match, then it’s a new tiger.
A camera-trap image of a tiger in the Upper Nilgiris, Tamil Nadu.
- For the tiger census results announced in 2018, camera traps were placed in over 26,000 locations, covering an area of over 380,000 sq.km. Images were collected over 1.5 years.
- Of the staggering of 3.5 crore photographs obtained, only 76,651 were of tigers.
- After processing these, it was concluded that there were around 3,000 tigers in the country.
There’s other information one can get as well. Take this example. Tourists photographed an adult tiger in Bandhavgarh but local guides felt this was a new tiger. Where did it come from? When officials at the Panna Tiger Reserve, 200km away, saw the images, they checked their database and identified it as Chote Pannalal from their reserve. By crossing the fields, villages, roads and mine areas between the two reserve areas, this tiger had established that the corridor between Bandhavgarh and Panna still existed. Images from camera traps have also helped identify the origins of tigers killed by poachers by matching the confiscated skins with patterns in the database.
These techniques are also used to protect other species like leopards, hyenas and other animals with patterns on their skins.
