Results and observation
1.1
An
intertidal bird survey was conducted on 2 November 2007. The weather was overcast and there was light
breeze. The temperature was 20oC
and the humidity was 66%.
Intertidal Mudflat Monitoring
1.2
Graph
4.1 shows the number and species of shorebirds recorded at the 100m x 100m mudflat
quadrats at NHS and SPN.
Graph 4.1 Comparison of
the Abundance and Species Composition of Shorebirds on the Exposed Mudflats
(100m x 100m Quadrat) at Ngau Hom Shek and Sheung Pak Nai – 2 November 2007
1.3
At
the NHS impact monitoring site, 4 species of 14 individuals of birds were
recorded; whereas at the SPN control site, 3 species of 12 individuals of birds
were recorded.
1.4
The
mudflats at NHS and SPN had very similar density of shorebirds (14 birds/ha and
12 birds/ha). The numbers of species at both sites were also very similar (4 at
NHS, 3 at SPN). The similar density and
species number suggest that the operation of HK-SWC had no obvious effect on
the shorebird communities during the survey on 2 November 2007.
1.5
Table
4.1 compares the density and number of shorebird species recorded during the
EIA and the recent survey.
Table 4.1 Density
and Number of Shorebird Species Recorded during the Previous EIA and the Survey
on 2 November 2007 on the Exposed Mudflats (100m x 100m Quadrat) at Ngau
Hom Shek and Sheung Pak Nai
|
|
Density of Shorebirds (Birds/Ha) |
No. of species |
||
|
|
Ngau Hom Shek |
Sheung Pak Nai |
Ngau Hom Shek |
Sheung Pak Nai |
|
Current Survey |
14 |
12 |
4 |
3 |
|
Previous EIA |
2.3 |
4.2 |
1.3 |
1.8 |
1.6
The
shorebird densities and the number of shorebird species at NHS and SPN recorded
during this survey were both higher than the numbers recording during EIA. The results of this survey suggest that the
operation of HK-SWC had no effect on the shorebird communities during this
survey.
1.7
The
density of shorebirds had an obvious increase during this survey when compared
to the previous operation monitoring survey conducted in September 2007. In the previous survey, there were only 2
birds/ha and 9 birds/ha at NHS and SPN respectively. During this survey, there
were 14 birds/ha and 12 birds/ha at NHS and SPN respectively. The increase in density could be explained by
the beginning of winter migration.
Migratory birds might have started to aggregate in the waters of
Tideline Monitoring
1.8
Graph
4.2 below presents the abundance and species composition of shorebirds recorded
on the 500m x 10m tideline transects at NHS and SPN.
Graph 4.2 Comparison of the
Abundance and Species Composition of Shorebirds along the Tidelines (
1.9
At
the NHS impact monitoring site, 5 species of 39 individuals of birds were
recorded; whereas at the SPN control site, 4 species of 36 individuals of birds
were recorded.
1.10
The
tideline transects at NHS and SPN had very similar
shorebird density (78 birds/ha and 72 birds/ha). The number of species at
both sites were also very similar (5 at NHS and 4 at SPN). The similar density and species of shorebird
suggest that the operation of HK-SWC had no obvious effect on the shorebird
communities during the survey on 2 November 2007.
1.11
Table
4.2 compares the density and number of shorebird species recorded during the
EIA and the recent survey.
Table 4.2 Density
and Number of Shorebird Species Recorded during the Previous EIA and the Survey
on 2 November 2007 along the Tidelines (500m x 10m transect) at Ngau Hom Shek
and Sheung Pak Nai
|
|
Density of shorebird (birds/ha) |
No. of species |
||
|
|
Ngau Hom Shek |
Sheung Pak Nai |
Ngau Hom Shek |
Sheung Pak Nai |
|
Current survey |
78 |
72 |
5 |
4 |
|
Previous EIA |
23.2 |
58.2 |
1.8 |
2 |
1.12
The
shorebird densities and the number of shorebird species at NHS and SPN recorded
during this survey were both higher than the numbers recording during EIA. The results of this survey suggest that the
operation of HK-SWC had no effect on the shorebird communities during this
survey.
1.13
The
density of shorebirds had an obvious increase during this survey when compared
to the previous survey conducted in September 2007. In the previous survey, there were 56
birds/ha and 58 birds/ha at NHS and SPN respectively; during this survey, there
were 78 birds/ha and 72 birds/ha at NHS and SPN. Migratory birds might have started to
aggregate in the waters of
1.14
A
parametric t-test found no statistically significant difference between the
bird abundance at NHS and SPN (P=0.738).
This further supports that the operation of HK-SWC has no impact on the
shorebirds communities at NHS during the survey.
Monitoring of Effects of Shade
1.15
During
the survey, the weather was overcast with clouds and there was no shade of HK-SWC
on the mudflat. As a result, no data for
‘In Shade’ was recorded during this survey. Only two sets of data, ‘Under
Bridge’ and ‘Exposed Mudflat’, were collected.
1.16
Graph
4.3 presents the results recorded during the survey for effects of shade on the
strips of mudflat (
Graph 4.3 Comparison
of Abundance and Species Composition of Shorebirds on the Strips of Mudflats (
1.17
At
the strip right under HK-SWC, 1 species of an individual of bird (Little Egret) were recorded;
whereas at the strip on the exposed mudflat, 4 species of 14 individuals of
birds (Little Egret, Great Egret, Chinese Pond Heron and Common Sandpiper) were
recorded.
1.18
The
results of the recent monitoring survey show that bird abundance on surveyed
area under HK-SWC was lower than that on exposed mudflat, suggesting that the
presence of the HK-SWC structure may have a potential impact on the distribution
of shorebird community.
1.19
While
only two sets of data were collected, the Kruskal-Wallis
test was used to test the statistical difference between the sets of data for
this survey. The non-parametric Kruskal-Wallis test suggests that there is a statistically
significant difference between the bird abundance right below the bridge and on
the exposed mudflat (P=0.008), although the sample size is small (n = 15).
1.20
Table
4.4 compares the results recorded during the previous survey (September 2007)
and the recent survey (2 November 2007) at the strips of mudflats (250m x 40m))
at Ngau Hom Shek.
|
|
Under Bridge |
Exposed Mudflat |
||
|
|
Sep 07 |
Nov 07 |
Sep 07 |
Nov 07 |
|
Abundance |
3 |
1 |
6 |
14 |
|
No. of Species |
2 |
1 |
3 |
4 |
1.21
It
is noted that results of the previous monitoring survey in September 2007 also showed
that a lower number of shorebird was recorded at the strip of mudflat right
under the bridge than on the exposed mudflat, though the difference was not
statistically significant. Compared with the results of September survey,
recent survey recorded similar bird abundance and number of species on surveyed
area under the bridge, but a higher number in abundance on surveyed area of
exposed mudflat. Overall, the total numbers of species recorded in these two
surveys are similar but that of bird abundance is higher in recent survey.
1.22
The
difference of total number in abundance between the two surveys may be taken
into account that the recent survey was conducted at the beginning of winter
migration season, when large population of winter visitors arrived in local
areas. The difference in shorebird abundance between the strips under the
bridge and on the exposed mudflat could possibly be amplified by this factor. Considering
that the abundance and species number remain similar and low at the strip under
the HK-SWC in September 2007 and November 2007 surveys, the difference between
the two strips of mudflat recorded in recent survey may not be as significant,
if the result is not affected by the influx of winter visitors.
1.23
Since
the substrates of mudflat under the bridge was disturbed by the construction
activities during construction phase of HK-SWC, it is suggested that benthos
communities in the mudflat under bridge have not re-established yet and food availability
of shorebirds may be limited, which may account for the lower number of waterbirds in this survey area. However, benthos
communities in mudflat under the bridge are expected to re-establish gradually in
a longer period and such factor would be diminished in the future.
1.24
Besides,
as level of mudflat along the shoreline is not even, the tideline
was observed to be in curve line at some locations. Since the shorebirds
usually stay at area near the tideline for feeding,
the more curved tideline at some location (e.g. exposed
mudflat) may provide more feeding opportunities for them, which may be a factor
affecting the distribution of waterbirds on the mudflat.
1.25
It
is also noted that the distribution of shorebirds on mudflat was uneven and
patchy in the nature. The survey area of exposed mudflat, which is located next
to the bridge alignment, was found utilized by group of shorebirds as feeding ground
while the other exposed mudflat next to the survey area more far away from the
HK-SWC bridge alignment was not found utilized by as many shorebirds as the
survey area. The uneven distribution of waterbirds
means that the population is not randomly distributed and may cause bias in
statistical analysis, especially when the data is lack of replication. Statistical
analysis using pooled data collected from 1-year monitoring may provide more
meaningful inference on the effects of bridge and its shade on the distribution
of waterbirds in Ngau Hom Shek.