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In this article we will discuss about how to conduct wildlife census.
Resource inventory is a pre-requisite for any management process. This holds good for wildlife management too. Practice of making inventory is not new to the forest department. Scientific management of forests in our country started in the late 19th century with preparation of working plans for the forests. List of plants and animals found in an area was carefully documented in the working plans and were updated regularly during the plan revisions.
During those days, timber production was given the top most priority of management and hence detailed account on population density of animals, their sex ratio, etc. were not made. However, certain areas like Corbett, Gir, etc. were managed with wildlife as the main focus.
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Wildlife received the much needed attention and the practice of managing areas exclusively for wildlife started growing across the world. This lead to the systematic inventory making of the wildlife resources at all levels (from a protected area to national to global level). Along with this, attempts were made to estimate the population of a species in an area. This process of estimating the population of a species/animal community is called as census.
Census started with simple counting of all individuals of a species in area to more complex methods involving statistical analysis. For a manager, is this number regarding a species enough? Not really, additional information about the population structure like age class and sex ratio helps the manager in proper decision making. Is information about just a species enough? Obviously No, because they live in communities along with various other species; all are inter-dependent and collectively they influence the ecosystem.
This necessitates collecting information on all major species so that by appropriate management interventions, they can be perpetuated for posterity. Further, the number of animals occupying a place too varies by season. Hence, census of animals in an area is not conducted as one time affair but done a periodical basis.
Census can be either conducted by direct counting or by indirect counting methods. In the direct count method the individuals are seen and counted whereas in indirect count method evidences left by animals are recorded to estimate the population.
1. Direct Count Method:
Under the direct count method either all the animals present in an area can be counted (total count) or can be done by sample counts. Sampling could vary from a simple random sampling to complex stratified sampling. Counting all the animals in area particularly large tracts involves lot of resources and hence should be avoided. Among the direct count method Vehicle transect and King’s census method is widely used in India.
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i. Vehicle Transect or Road Count Method:
Vehicle transect involves counting of animals on roads by travelling in a vehicle at a fixed speed and during a fixed time. The distance for such transect is fixed and the counting is done on the transect regularly.
Density of the animal is calculated using the formula given below:
When the density figures of corresponding period are compared, they give a clear picture about the trend of the population. Say density of Peacock calculated in the month of April should be compared with the density figure of April the next year to arrive at a reasonable conclusion regarding the population trend. Transects should be placed in such a way that they cover all types of ecosystems found in an area. Adequate number of transects should be placed to capture the real picture of the area.
ii. King’s Census:
Under the King’s census, data regarding sighting of animals is collected from transects by the observers walking on transects. Transects are laid to cover all the ecosystems present in an area. Any single transect laid should as far as possible cut across all the vegetation type/ecosystem. If there are grasslands, shrub land and forests, then the transect should run through all these three vegetation type and not just one.
An observer along with one more person walks on the transect preferably in the early morning hours and record all the sightings on the transect with the angle of sighting and distance (angular distance). With the angular distance and angle of sighting the perpendicular distance of animals from the transect line is calculated. This perpendicular distance is used in calculating the area of the transect walked. The density of animals is calculated with the use of the formula.
Width of the transect could be varying like the one illustrated above or may be fixed. In the fixed width transect (generally done in areas with good ground visibility), the width of the transect is fixed and the observations beyond the fixed width is not recorded. Density calculated for a particular transect is then extrapolated for similar areas to arrive at density figures for the entire area.
2. Indirect Count Method:
The pug mark technique is one of the indirect count method still widely used in our country for estimation of larger carnivores like tiger and leopard. Generally, Pellet count method is used to estimate the ungulate density in most of the protected areas in our country.
Under pellet count method, pellet groups are counted in sample plots preferably laid out on the transects (laid for conducting King’s Census) and the density of the animals (species wise is estimated) is calculated with the data collected on the number of pellet groups. Information on defecation rate for animal surveyed, knowledge on pellet size and pellet rate in a day is required.
3. Other Methods:
Apart from the methods discussed above there are certain methods which are not included in the direct or indirect count method viz.:
i. Water hole census
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ii. Capture-recapture method
i. Water Hole Census:
In absence of trained and experienced staff, generally “Water Hole Census” is conducted to estimate the densities of animals. In this method, observations on sighting are collected at water holes (during summer) for 24 hours preferably from 6 PM to 6 PM on full moon days. The basic assumptions made in this method are that every animal has an equal opportunity to visit a water hole and every animal drinks water at least once in a day.
Number of animals sighted are counted and recorded throughout the 24 hours and later on, the data is compiled species wise to arrive at the density figures. This method also gives an index or trend regarding the population and not the estimate of the population. If information on frequency of water consumption by animals for the area is collected, the figures compiled can be corrected for the repeat visitors and the trend can be refined a little. This is one of the easiest methods and with little training (along with volunteers from colleges, NGO’s, etc.) even the illiterate staff can collect some useful information. For these reasons, this is the most popular method in many parts of our country.
ii. Capture-Recapture Method:
This is neither a direct method nor indirect method but a combination of certain elements from both. This method is used in monitoring works of turtles, tortoises, crocodiles, birds, etc. First, certain numbers of animals are captured, marked and released. Second, again some animals are captured from the same area and checked for the marked animals.
From the ratio of the marked and unmarked animals an estimate regarding the population can be made using the following formula:
