Tracking Tigers: Guidelines for Estimating Wild Tiger Populations Using the Pugmark Technique

1. What they did

For decades India’s tigers were counted every four years from their footprints, called pugmarks. The preface explains that the method was applied unevenly: sometimes the left foot was measured, sometimes the right, sometimes the front, and field staff were rarely trained. This revised manual, written by tiger researcher L.A.K. Singh for the WWF Tiger Conservation Programme, sets out one standard way of doing it, so that forest guards and their supervisors can be trained in it.

The guide has three parts:

• Biological background. How tigers hold territories, what a pugmark looks like and how soil changes it, how tigers walk, and how to tell tiger tracks from those of leopards and other animals, front from hind, left from right, and male from female.
• Collecting field data. Seasons, schedules, training, field kits, building Pug Impression Pads, and how to trace pugmarks and make plaster casts.
• Analysis and reporting. How tracings are sorted and compared to pick out individual tigers and leopards, and how counts are reported from range to state level, with the data forms in the annexures.

The method aims at a reasonably reliable minimum number of tigers in an area, not a complete count.

2. What they found

Biological basis

• The method rests on territoriality. In good habitats adult males hold large territories that overlap smaller female ones; in medium habitats territories overlap more and transient tigers are more common; in poor habitats territories may be absent. Within the short count period, territory holders do not change, which helps avoid counting the same tiger twice.
• If tracks are recorded systematically over one or two weeks, the tracks of all tigers in an area can be picked up.

Reading the pugmark

• A tiger’s print shows four toes in a semicircle above a pad that has three lobes at the back. The front paw is always larger than the hind paw.
• At a normal walk the hind foot lands on or partly over the front print, so only hind prints are usually intact. The count therefore uses hind pugmarks. In a slow walk the hind print falls behind the front one; in a fast walk it falls ahead.
• Soft slush or coarse sand splays a print and makes the pad look bigger; firm ground with a little dust gives a true print. A pebble can shift a toe.
• Left or right: the leading toe is second from the right on a right foot, and second from the left on a left foot.
• Sexing: a box drawn around a hind print is close to square in males and clearly rectangular in females. Male toe prints tend to be round or oval, female ones longer. In adult males the front print is often wider than long. A ready reckoner (Table 1), built from Simlipal data, gives expected widths for males and females at each length. The guide warns against relying on it alone: in doubt, record “sex unknown”.
• Tiger cub or adult leopard: an adult leopard’s print is about the size of a four month old cub’s. A tiger’s stride is about 10 times its hind print length, a leopard’s 12 to 14 times; with a print of about 9 cm, a cub’s stride is about 80 to 90 cm and a leopard’s over 100 cm. A tiger’s toes are larger relative to the pad. A cub that small would only move with its mother, so if no adult female prints are present, the tracks are taken as a leopard’s.
• Other animals: elephant and rhino tracks, and hoofed animals’ tracks, are easy to separate. Dogs, jackals, hyaenas, wolves, bears and ratels leave claw marks; ratels can confuse beginners but have two lobes at the back of the pad. Cats leave no claw marks.
• Age of the print: fresh prints have sharp edges; wind and dew soften them by the end of one day, though prints near water can last a week or more. Dew in winter leaves drizzle-like marks, so prints on dewy soil were made in the early morning. The guide calls ageing a “fine art” that needs much skill and should not be a mainstream part of the method.
• Look-alike prints in the same or nearby areas are rare and may be siblings. They are counted as one animal unless clearly separated by distance, stride, injury marks or other measurements.

Field work

• Best season: the dry season, December to March; second best, September to November.
• At least seven consecutive field days: all routes searched on days one to three, searched again in the same order on days four to six, with rechecks on day seven.
• Each field unit has three people, at least one knowing the area well. Two keep watch while the third kneels to trace or cast.
• Training runs down from state to range level, starting 60 days ahead. Tourist traffic and similar work should be stopped or restricted, and vehicles kept off routes until 9 am.
• Pug Impression Pads (PIPs): where ground is grassy, hard, rocky or leaf-covered, a strip across the whole road, at least 2 m long, is dug out 2 to 3 cm and filled with finely sieved earth. Pads are laid at least seven days before the count, freshened two to three days before, checked at least twice, and swept clean with a leafy branch after each reading. Clusters of three or four pads, 50 to 100 m apart, go at crossroads and every 500 to 1000 m. Ash is discouraged because it may lead to burning leaves.
• Stride is measured first, then the best hind print is traced on a glass “Tiger Tracer” with the tracer’s eyes directly above it, then a plaster cast is made (about 350 ml of water, a 2 cm wall around a print at least 2 to 3 mm deep). Prints are wiped out after recording.

Analysis

• Tracings of other species are screened out, then lesser cats by size.
• Tracings are coded and linked to their casts; a poor tracing can be redrawn from a good cast pressed into damp sand. The direction of walk comes from the trail, not a single print.
• Prints are boxed and measured, sorted into leopard, tiger cub, male and female, then grouped. Mother and cub groups are accepted on at least one clear set of trails moving together.
• Similar tracings are laid over each other against the light. Six features separate individuals: the shape and slope of the pad’s top edge; the shape and sag of the two side lobes; the shape and size of the middle lobe; the direction the lobe junctions point; a constant distance between pad and leading toe; and repeated injury marks or a consistent paw twist.
• Accepted tracings record each tiger’s measurements and the places it was found (its movement area). Overlaps are removed between neighbouring units, ranges and divisions, and results are mapped by sex and age.

3. What they concluded

• Done on a large scale in a week or two by field staff with limited training, the method can only give broadly reliable estimates, and this should be considered adequate. Used consistently by skilled people over long periods in one area, it can give fairly accurate results on numbers, sex and age structure and ranging.
• It is called the most cost-effective method and the least demanding of equipment, at any scale.
• The preface and foreword accept that the method is controversial and has weaknesses: no method is 100% accurate, there is no foolproof check against deliberately false data, and other methods should be developed and used where practical. A special approach is needed for the Sundarbans mangroves.
• The aim is to standardize the method and build the skills of field staff. The ready reckoner should be tested in other places.

4. How tracking was or was not used

The whole manual is about tracking. It covers tracks and signs identification (telling tiger and leopard prints from other species, front from hind, left from right, male from female, and cub from adult), measuring prints and strides, reading gait, ageing prints, making artificial track pads, recording prints by tracing and plaster casting, and identifying individual animals from their prints. Direction of travel is read from a trail of prints. Kill and sighting records from field staff support the analysis.

5. Tracker or observer certification

No certification or skill test is described. The counts are made by forest guards in three-person field units, at least one member knowing the area, after short training sessions held from 60 to 10 days before the count. The guide stresses that the method needs experience and skill, especially for ageing prints and for the analysis, and says field staff can acquire only limited skills through training.

6. Other technologies, skills or innovations

• The Tiger Tracer: a glass plate held just above the print for tracing, then retraced onto a data form.
• Pug Impression Pads to record tracks on ground that does not hold them.
• Plaster of Paris casts, and redrawing a print by pressing a cast into damp sand.
• A ready reckoner table for sexing tigers from hind print length and breadth.
• Standard data forms (A to G) for habitat, past records, other animals, daily logs, tracings and range, division and circle summaries.

7. Implications for conservation (from the paper)

• Tiger numbers need to be estimated regularly, but the preface warns that counting has become a “numbers game”, with managers judged on tiger increases, so that few believe the figures. Saving tigers also means saving their prey and the ecosystems they live in.
• A standard, well-taught method used across the country would give more reliable population estimates for tiger, leopard and lion.