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Detailed Ecological Assessment Report 2008 – Keenjhar Lake
2.3.6 Identification of species
The specimens were identified with the help of most recent keys available
in literature (Khan, 2003, 2006).
2.3.7 Data analysis
There are several numerical indices in use, which quantitatively describe different
levels of diversity and evenness in samples collected from different localities or at
different times from the same environment. One such commonly used diversity
index is called “Shannon-weaver” index of diversity, which combines the number
of species present and evenness into a single index. The formula is given as: D =
-Σ pi in pi where “i” stands for an index number for each species present in a
sample, “pi” can be calculated through “ni/N” in which “ni” represents the number
of individuals within a species divided by the total number of individuals “N”
present in the entire sample and “ln” stands for natural log. In this way the
proportion “pi” of each species in the sample times the natural log of that same
value “ln pi” the values for each species and finally multiplied by –1. The value of
“D” is always higher when species are equally abundant. Similarly species
evenness is calculated by the formula as: E = eD/s, where “e” is the Shannonweaver
constant valuing 2.7, “D” is the value of Shannon-weaver index and “s”
represents the number of total species in a sample. Species evenness, thus,
separates the effect of different population sizes (number of individuals within
species) from number of species (species diversity).
2.4 Birds
2.4.1 Survey method
Each major habitat type in the study area was identified and records were kept of
species of birds found in each discreet habitat such as lakes, canals, ponds,
marshes, coastal areas, creeks, forest, agriculture fields, mangrove areas, vicinity
of human habitation and fallow lands. The number of birds observed in each
habitat type was also recorded with particular emphasis on the key species and
to relate the data to other components of the study area such as vegetation,
water and soil etc.
The most commonly used field method in bird surveying is the “Line Transects”
method. It is based on recording birds continually along a predefined route within
a predefined survey unit. It can be used in terrestrial, freshwater, and marine
systems to survey individual species, or group of species. It is used to examine
bird-habitat relationships and to derive relative and absolute measures of bird
abundance.
Line Transects are suitable for extensive, open and uniform habitats and for large
and conspicuous species. Double counting of birds becomes a minor issue as the
observer is continually on the move. Line Transects are suited to situations where
access is good and these are very useful for bird-habitat studies (Gregory et al
2004).
In the present studies, each sample area was transversed / examined by 2
observers, separately. Birds were searched on each side of the strip for 150m so
that each study strip was 300m wide. Use of binoculars and telescopes was
made to identify bird species, count or assess bird numbers, particularly in case
of water-birds.
WWF Pakistan – Indus for All Programme Page 29 of 165