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Problems of identification of camera-trapped tigers
Indian Wildlife - challenges in the new millennium
The greying of India
On the road to extinction
A Tribute to Rumbha - the elephant  
State development project threatens state bird - Sarus
Shahtoosh ban gains momentum worldwide
The road to disaster
Killing nilgais in the name of crop protection
Warring NGO's may spell doom for the tiger
Where have all the sparrows gone?
Cuckoos that fly out of crows' nests
Corbett park woes continue to mount
A question on post mortem examinations in the wild
Is it time to 'cry wolf' again?
Lifting of US sanctions may boost wildlife conservation
Migratory waterfowl may be hit by war in Afghanistan
UP wetlands to provide improved habitat to waterfowl
Anthrax as a potent wildlife killer
Man-elephant conflict takes heavy toll
Demoiselle cranes fly to safety in India
How long lasting are conservation victories
Fake tiger skins : a knotty disguise
Who cares for the wild here anyway?
A tribute to Charger - the long living tiger
Draining of wetlands threatening wildlife
Wildlife management needs rapid response units
Dudhwa loses another tiger
Indian Wildlife Board meets after five years
Problems of identification of camera-trapped tigers
by S.P. Goyal and A.J.T. Johnsingh
( Wildlife Institute of India, Dehra Dun 248001, India )

One of the major problems facing tiger conservation today is our inability to accurately estimate the population in a given tract. Population estimation based on pugmarks, the traditional method (Choudhury, 1970; Panwar 1979), has been questioned (Karanth 1995) as most of the parameters used for population estimation have not been statistically validated. Gore et al. (1993) concluded that sex can be identified, but the technique for individual identification needs to be refined.    

It is believed that individual tigers can be identified based on facial markings and stripe patterns (Champion 1927, Schaller 1967, McDougal 1977). Based on this assumption, Karanth (1995) had applied capture-recapture technique for tiger population estimation. He used self-activated cameras to identify individual tigers based on stripe pattern. Data on individuals identified during a time period were then used to estimate the population.    

Since December 1994, in Dholkhand, the mini-core area in Rajaji National Park in north-western India, we have been using self-activated camera units to photograph tigers. Till November 1995, tigers were photographed six times over 85 camera trap nights. Three new facets about the use of camera trap technique arose when we asked our colleagues at the Institute to identify individual tigers based on these photographs. In one case, the face of a tiger was photographed twice with a time difference of nine seconds. In the first picture, one of the face stripes is connected with the eye and in the second, due to a slight change in posture, the stripe looks as if separated from the eye. This had made 100% of our colleagues (N=20) identify the photographs as belonging to two different tigers.    

Another time, two photographs of the lateral side of a tiger were taken one after the other. All (N=l3) identified them as two different individuals. The track data, however, had shown that only one tiger had walked in front of the camera. When we examined the face pictures of these two tiger photographs, 10 major stripes were seen in both the pictures. But in the second picture a loop had been formed due to a change in posture, Seventy-eight per cent of our colleagues (N=9) identified these face pictures as belonging to two animals.    

When we critically looked at the reason for this confusion we discovered that 24 stripes above the belly and shoulder were identical in both the photographs. There were considerable variations, however, between the two photographs when the stripe pattern on the flank above the elbow joint and hind quarters of the body were compared. We observed similar variations in the stripe pattern of a tiger photographed in Delhi Zoo. The left side of the tiger was photographed three times and the right side four times. When photographs of a particular side were compared to one another, all showed individual variations. These variations are attributed to the loose nature of the skin on the upper parts of the body. As a result, slight changes in the body posture bring about variations in the way stripes appear from one photograph to the other.    

1.Movements are likely to cause least variations in the stripes on the face as the skin is tight. But we have to ascertain, based on photographs of captive animals, whether there are enough variations in face stripes to identify individuals.

2.Shift in posture causes considerable variations in the stripe patterns on the hind quarters and flank above the elbow joint and this is attributed to the loose nature of the skin on these parts of the body.   

3.Stripes above the belly and shoulder show least variations due to movements. This, however, needs to be ascertained with a large sample from captive tigers.     

We conclude that identifying individual tigers based on stripe patterns may not be as easy as it appears to be. Variations could appear in photographs of the same animal due to slight changes in posture. These findings need to be taken into account in any future programme to estimate the population of tigers based on camera traps.