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Title
Remote sensing for resources development and environmental management
Author
Damen, M. C. J.

The habitat categories 31 and 34 most
accurately represent the conditions of the
woodlands surveyed by Woolhouse. The total
area of these habitats can thus be used to
predict bird species numbers. However, these
conclusions can only be accepted tentatively.
This apparent relationship may have occurred
purely by chance. Unfortunately field data
only exists for one year therefore the
relationship cannot be retested. A backup
test was conducted. If the relationship
between the total habitat area of categories
31 and 34 and the number of breeding species
was real, one would expect all the bird
species which breed to have either 31 or 34
as one of their habitat requirements. It was
found that 20 of the 27 species known to
breed in Saltswells wood had habitats 31 or
34 listed as one of their preferred habitat
types. This leaves the breeding of 7 species
unexplained. Two conflicting conclusions can
be drawn. The apparent relationship between
the actual number of breeding bird species
and the number estimated using the Woolhouse
equation has occurred by chance or the
relationship is real but the habitat patterns
allocated to each bird species are
inaccurate. The results of this analysis
remain therefore inconclusive and indicate
that further work needs to be conducted.
Woolhouse, in the same paper also suggests
that species abundance can be predicted from
the area of woodland.
In I = 0.679 In A + 3.082
Where In I is the natural log of species
abundance.
Using the total habitat area of categories 31
and 34 the expected number of individuals is
174.12. However, according to the field data
289 individual birds were recorded. This
large discrepancy suggests that this equation
may not be used with the area totals of 31
and 34 identified from the air photographs
for urban woodlands. The field data
collected by Woolhouse was obtained in rural
woodlands. Various studies about bird
populations in urban environments for
example, Emlen 1974, Tomialojc and Profus,
1977 suggest that although species numbers
are lower in urban environments than rural,
actual bird densities are often higher in
urban areas. As Saltswells wood is an urban
wood this may be the cause of the
discrepancy.
There is not enough evidence available to
indicate whether the equation put forward in
the literature concerning the relationship
between area and bird species numbers can be
used successfully with air photographs. The
results of the analysis are inconclusive.
However this does not necessarily suggest
that it is impossible to predict the bird
carrying capacity of a wood from habitat area
data extracted from air photographs.
Further analysis was conducted by
calculating the total amount of suitable
habitat available in the reserve for each
likely bird species.
The photographic area data suggested that the
species which were identified as breeding in
the field survey were those which had the
largest area of suitable habitat available in
the reserve. Two statistical tests, Chi^ and
Mann Whitney U test were conducted to
investigate whether the available habitat
totals for breeding and non-breeding species
were from the same population or whether
there was a significant difference between
Table 2. Species habitat area
Bird
Species
Suitable Habitat
categories
Total
area
habitat
(ha)
Black bird
34/43/44/45
16.95
Woodwarbler
31
14.43
Willow
Warbler
44/45
1.02
the two groups. The rejection level in both
instances was 0.05.
The Chi^ test suggested there was no
difference between the area totals but the
Mann Whitney U test indicated that there was
a significant difference, that is, the bird
species which are found to breed in the
reserve are those with the largest amount of
habitat available to them. However this test
does not indicate the magnitude of the
difference, nor does it provide any
indication of a critical value of available
area above which bird species are likly to
breed. The parameters needed for prediction
have not been identified.
Further tests were thus felt necessary to
discover whether any other differences could
be identified from air photographs between
the habitats of breeding and non-breeding
species. It was believed the level of
dispersion of suitable habitat types may have
an influence on whether a bird species
breeds. The previous tests have looked at
the relationship between the numbers of
breeding birds and the total amount of
suitable habitat. However in reality, in the
reserve, the habitat types are fragmented
into a number of small units rather than
individual large blocks.
This fragmentation may result in suitable
habitat blocks being below the territorial
requirements of an individual species so
being of little use. It was therefore
suggested that the bird species with the
least divided habitat will be more likely to
breed. They will have more chance of finding
a suitable sized block of the required
habitat type.
It is easy to identify the number of units
of each habitat type from the air
photographs. Mann Whitney U tests were
carried out on data from breeding and
non-breeding birds. The tests looked at:
a) whether any significant difference
existed between the numbers of units of
suitable habitat for breeding and
non-breeding bird species,
b) whether any significant difference
existed between the amount of area per unit
and
c) whether any significant difference
existed between the average number of units
per habitat type for breeding and
non-breeding species.
In each instance the rejection level was
set at 0.05. In each case no significant
difference was found. No conclusison could
therefore be drawn about the affects of
habitat unit dispersion and the likelihood of
birds breeding in the urban woodland.
6 CONCLUSION
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literature concerning the usefulness of
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