STUDYING TIGERS
By Dr. Anish Andheria.
Dr.
Anish Andheria, a wildlife biologist, is the director of both the Wildlife
Conservation Trust and Sanctuary Asia .
Wildlife areas certainly need to be
free of human interference, but it is also essential that we study our forests
to know exactly what is happening within them. The biodiversity value of
forests is measured in the health and numbers of their wildlife populations and
communities.
Science is a tool for the proper
management of Protected Areas and helps us gauge whether the protection enjoyed
by the forest is adequate and whether the strategies adopted to sustain and
increase faunal and floral populations are legitimate and effective. In recent
years in India
Radiotelemetry is probably the best
technique to generate information about the movements and behaviour of cats. It
involves tranquilising the animal and then attaching a light, unobtrusive
collar containing a radio transmitter around its neck. With the help of a
receiver and an antenna, researchers can then follow the animal and record its
activities. Most of the existing information we have about tigers can be
attributed to radiotelemetry studies.
The camera-trapping method has proven
to be the most reliable method of estimating tiger population densities. The
equipment used for this method of enumeration consists of two cameras with
inbuilt flash, one infrared transmitter, one receiver and two metal housings to
protect this equipment from animals and weather. One camera each is mounted on
a post approximately 3-4 meters away on either side of a forest road or an
animal path. The infrared beam is set just below the camera at a height of approximately
half a meter from the ground. Tigers regularly patrol forest trails,
communicating with other tigers through scent markings. Camera-trap points are
selected based on the presence of tiger signs such as scats, scrapes, tracks,
claw markings and scent deposits along these forest trails. Date, time and
location of each photographic capture of a tiger are noted and the shapes and
stripe pattern and position of the photographed individuals are carefully
compared to minimise confusion. Each tiger has a unique stripe pattern just as
every human has a unique finger print. The differences in the stripe pattern
are used to differentiate every single photo-captured tiger from the other.
Additionally, prey density is also an
important measure of the carnivore carrying capacity of an area. Line Transect
Sampling of prey was developed to estimate this. This method involves walking
along demarcated routes every morning and evening when animal activity is at
its peak and counting the number of individuals of a prey species seen along
with their distance from the observer. The special focus of line transect is on
species that form the bulk of the tiger’s diet. In India
Data collected by a combination of
such scientific methods gives us the best results. Till very recently, apart
from direct sightings, the only method used for calculating tiger densities was
pugmark identification using tracers and plaster. However, this technique was
ad hoc and now it is widely accepted that pugmarks can at best provide
additional information about tiger movements and are not good enough for
identifying individual tigers and therefore tiger densities.
A widely-used field technique for
understanding the tiger’s diet is identification of recognisable parts of prey
in their scats. Scats provide a snapshot of types of prey consumed and have an
advantage over other techniques because of the relative ease of obtaining
samples and the non-destructive nature of the sampling procedure. New molecular
biological techniques for extracting DNA of tigers from their scats and the
ability to identify individual tigers using this DNA offers another method for
estimating the abundance of tigers. Continued progress in improving the
accuracy of individual identification from scat derived DNA makes it
increasingly relevant in estimating tiger numbers in the future.
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