Results and observation
1.1
The intertidal bird surveys were conducted on 16
January 2009. The weather was fine and
the sky was foggy. The temperature ranged
from 8.6 to 18.2oC, and the humidity ranged from 47 to 80%.
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 Abundance and Species Composition of Shorebirds on the Exposed Mudflats (100m x 100m Quadrat) at Ngau Hom Shek and Sheung Pak Nai – 16 January 2009
1.3
At the NHS impact
monitoring site, four species of 23 individuals of shorebirds (Great Egret Egretta alba, Little Egret Egretta garzetta, Eurasian Curlew Numenius arquata and Grey Heron Ardea cinerea) were recorded; whereas at the SPN control site, seven species of 17
individuals of shorebirds (Great Egret Egretta alba, Little Egret Egretta garzetta,
Eurasian Curlew Numenius arquata, Grey Heron Ardea cinerea, Osprey Pandion haliaetus, White Wagtail Motacilla
alba and Little Ringed Plover Charadrius dubius) were recorded.
1.4
The
intertidal mudflat quadrats at the NHS impact site
and SPN control site recorded approximately the same abundance and diversity of
shorebirds, indicating that shorebird communities are not adversely affected by
the operation of the HK-SWC.
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 16 January 2009 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 |
23 |
17 |
4 |
7 |
|
Previous EIA |
2.3 |
4.2 |
1.3 |
1.8 |
1.6
The
shorebird density and diversity 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 and abundance of shorebirds recorded during this survey were higher
than the previous monitoring survey conducted in November 2008 (three species
of 11 individuals at NHS, and one species of three individuals at SPN). The density and abundance recorded during winter
months are often higher than those recorded in other months, as a large
population of passage migrants and winter visitors has arrived in
Tideline Monitoring
1.8
Graph
4.2 presents the abundance and species composition of shorebirds recorded on
the 500m x 10m tideline transects at NHS and SPN.
Graph 4.2 Abundance and Species Composition of Shorebirds
along the Tidelines (
1.9
At the NHS impact
monitoring site, six species of 162 individuals of shorebirds (Great Egret Egretta alba, Little Egret Egretta garzetta, Grey Heron Ardea cinerea, Chinese Pond
Heron Ardeola bacchus, Eurasian Curlew Numenius
arquata and Black-capped
Kingfisher Halcyon pileata) were recorded; whereas at the SPN control site, six species of 46
individuals of shorebirds (Great Egret Egretta alba, Little Egret Egretta garzetta, Grey Heron Ardea cinerea, Common Sandpiper Actitis
hypoleucos, Great Cormorant Phalacrocorax
carbo, and Little Ringed Plover Charadrius dubius) were recorded.
1.10
The
tideline transects at the NHS impact site and SPN
control site recorded the same diversity of shorebirds, while NHS recorded a
higher abundance. The results indicate
that the shorebird communities were not adversely affected by the operation of
the HK-SWC during the survey.
1.11
A
parametric t-test suggests that there is statistically significant difference
between the bird abundance along the tidelines at NHS
and SPN (p<0.001). Nevertheless, the diversity at both sites is
the same, and that the NHS impact site has higher shorebird abundance than the
SPN control site. Therefore it is considered
that the operation of HK-SWC has no impact on the shorebird communities at NHS
during the survey.
1.12
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 16 January 2009
along the Tidelines (
|
|
Density of shorebird (birds/ha) |
No. of species |
||
|
|
Ngau Hom Shek |
Sheung Pak Nai |
Ngau Hom Shek |
Sheung Pak Nai |
|
Current survey |
324 |
92 |
6 |
6 |
|
Previous EIA |
23.2 |
58.2 |
1.8 |
2 |
1.13
The shorebird density and diversity at both of the NHS
and SPN sites
recorded during this survey is higher than that recorded during the previous
EIA, indicating that
the operation of HK-SWC had no effect on the shorebird communities during this survey.
1.14
The densities of shorebirds at NHS and SPN recorded
during this survey were higher than the previous survey conducted in November
2008. In the previous survey, there were
140 birds/ha and 54 birds/ha at NHS and SPN respectively; during this survey,
there were 324 birds/ha and 92 birds/ha at NHS and SPN. For species diversity, the numbers recorded
during this survey, six for NHS and six for SPN, were about the same as those
recorded in the November 2008 survey, five for NHS and eight for SPN.
Monitoring of Effects of Shade
1.15
During
the survey, three sets of data, ‘In Shade’, ‘Under Bridge’ and ‘On 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 Abundance and Species Composition
of Shorebirds on the Strips of Mudflats (
1.17
At
the strip of mudflat right under HK-SWC (Under Bridge), two species (Little Egret Egretta garzetta and Grey Heron Ardea cinerea) of five individuals were recorded; where ‘Under Shade’, four species (Great Egret Egretta alba, Little Egret Egretta garzetta, Black-capped Kingfisher Halcyon pileata and Grey Heron Ardea cinerea) of eight individuals were recorded;
and that two species of ten individuals (Great Egret Egretta alba and Little Egret Egretta garzett) were recorded on exposed mudflat.
1.18
The
recent monitoring survey show that shorebird abundance on the surveyed area “Under
Bridge” and “In Shade” were slightly lower than that on “Exposed Mudflat”, suggesting
that the operation of the HK-SWC may have potential impacts on the distribution
of shorebird community.
1.19
As
discussed in the operation monitoring report dated November 2007, distribution
of shorebirds may be affected by a number of abiotic
or biotic factors apart from the operation of the HK-SWC, and they are listed
below:
l
Early-staged
establishment of benthos communities in the mudflat under bridge after the
construction phase provide less food resource for shorebirds, which may account
for the lower number of shorebirds recorded under the bridge. However, benthos communities in mudflat under
the bridge are expected to build up gradually in long-term and such factor should
be diminished in the future.
l
The
curve-shaped tideline at some locations may provide
less feeding area and feeding opportunities for shorebirds, which may affect
their distribution at NHS.
l
The
uneven and patchy distribution of shorebirds in nature means that it may cause
bias in statistical analysis.
l
A succession of oyster farms was
found located on the mudflat approximately
1.20
A
statistical one-way anova test found no statistically
significant difference between the bird abundance within the mudflats ‘In shade’,
‘Under Bridge’ and ‘On Exposed Mudflat’ (p=0.6559). This result suggests that
the physical existence of the HK-SWC and its shade has no significant adverse impact
on the shorebird communities at NHS during the recent survey.