This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Thimmayya, a Jenu Kuruba tribesman who lives in the Nagarahole Tiger Reserve is leading the way. Following him is Killivalavan Rayar, a senior research associate working with WCS India Program. They tread along a forested trail, silent and observant. Suddenly, to the left, they hear a crack made by the snapping of a branch. The sound is all too familiar. Thimmayya turns towards the researcher and points out a large, gray figure feeding in a nearby thicket. Elephant!
Careful to not alarm the animal, lest it move, or worse, charge towards the duo, the researcher lifts a laser range finder to measure the distance of the elephant from the trail they were walking. This trail is a “line transect,” and we walk them every year across the Malenadu region to count deer, pigs, elephants and more.
Tigers are the largest cats in the world. In Malenadu, adult females average in excess of 120 kilograms in body mass and about 100 inches in body length, while males grow considerably larger. Sustaining such large frames require prey species in good abundance––a tigress for instance needs to feed on approximately 50 mid-sized deer weighing about 60 kilograms each to survive the year. Each tiger in fact needs a pool of about 500 mid-sized deer within its home range to support its annual diet. Healthy populations of prey species thus hold the key to tigers surviving and reproducing in the wild.
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Counting tiger prey is a key research activity that we undertake in Malenadu each year. We carry out these counts while walking along systematically placed trails known as line transects. A transect is a straight line through a forest, on either side of which, we count the animals that we see––the species we count range from the 20-kilogram muntjac to the 3-ton Asian elephant. We also record radial distances and compass bearings of the observed animals to the line. This allows us to estimate how far from the line animals can be effectively counted, and how the chances of us spotting an animal varies with distance from the transect line. We thus account for the possibility that not all prey animals may be seen during transect surveys, working on the assumption that the best chance of us seeing an animal is on or near the transect line.
Before these transects can be walked, however, there is a lot of preparatory grunt work that needs to be done. At the start of the field season, our research teams first mark out the transect lines that are to be walked. During our initial years of research in the late 1980s and 1990s, we would mark and walk transects that were simple straight lines. But the logistics of dropping and picking up observers walking such lines can be a real test of efficiency for even the most organized of field managers!
We have since modified our survey design in favor of transects that are in the shape of a square, thereby allowing observers to end where they began. We mark these square transects with red paint, ensuring that each arm of the square is a straight line 800 meters in length, with every 100 meter segment marked. About 40 to 50 such transects dot each of our study reserves within Malenadu, adequately and systematically covering the expanse of a given reserve and allowing reliable estimation of prey abundance therein. More importantly, in addition to estimating prey numbers, we use this field data to see which conservation interventions are actually helping. The analysis relies on advanced techniques and provides useful feedback to the managers of protected areas.
The transects need to be walked within a short span of 20–30 days, as a transect survey is meant to be a snapshot in time. To add to this challenge, each transect has to be walked multiple times to ensure sufficient replication of the survey effort. Manpower––warm bodies of sweat and blood, impervious to biting ticks and sucking leeches––is thus essential to complete this task we set for ourselves each year.
Dr. Ullas Karanth devised a ‘citizen science solution’ to the problem. He engages volunteers thirsting for time in the wilds of Malenadu and provides them with field training before recruiting them to walk the lines. Many of the transect volunteers are committed wildlife professionals today, pursuing the science and conservation of species such as the endangered tiger far and wide.
For previous posts in this series, "Along the Tiger's Trail," click here.