Results and observation
1.1
The intertidal bird surveys were conducted on 20 November
2008. The weather was fine and sunny. The temperature was between 13-21oC
and the humidity was between 49-66%.
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 Abundance and Species Composition of Shorebirds on the Exposed Mudflats (100m x 100m Quadrat) at Ngau Hom Shek and Sheung Pak Nai – 20 November 2008
1.3
At
the NHS impact monitoring site, three species (Little Egret Egretta alba, White-breasted Kingfisher Halcyon smyrnensis and Eurasian
Curlew Numenius arquata) of 11 individuals were recorded;
whereas at the SPN control site, one species (Little Egret Egretta alba) of three individuals were recorded during the
survey. While higher diversity and
abundance were recorded at the NHS impact monitoring site, there was no
evidence to suggest any adverse impacts from SWC operation on shorebird
communities during the survey.
1.4
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 20 November 2008 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 |
11 |
3 |
3 |
1 |
|
Previous EIA |
2.3 |
4.2 |
1.3 |
1.8 |
1.5
The
shorebird density and diversity at NHS recorded during this survey were higher
than the numbers recorded during EIA. These results suggest that the operation
of HK-SWC had no effect on the shorebird communities during this survey.
1.6
The abundance and diversity of
shorebirds recorded at NHS during this survey (three species of 11 individuals)
were similar to the previous monitoring survey conducted in September 2008 (two
species of 11 individuals). The
densities recorded during the recent surveys (November, September, July and May
2008) were lower than those recorded in winter months (e.g. January 2008), when
large population of passage migrants and winter visitors in local areas could be
the cause of the higher numbers.
Tideline Monitoring
1.7
Graph
4.2 presents the abundance and species composition of shorebirds recorded on
the
Graph 4.2 Abundance
and Species Composition of Shorebirds along the Tidelines (
1.8
At the NHS impact
monitoring site, five species of 70 individuals of shorebirds (Great Egret Egretta alba, Little Egret Egretta garzetta, Grey Heron Ardea cinerea, Chinese Pond Heron Ardeola bacchus, and
White-breasted Kingfisher Halcyon smyrnensis) were recorded; whereas at the SPN control
site, eight species of 27 individuals of shorebirds (Great Egret Egretta alba, Little Egret Egretta garzetta, Grey Heron Ardea cinerea, Euraisan Curlew Numenius arquata, Common
Sandpiper Actitis hypoleucos,
Little Ringed Plover Charadrius dubius, Red-rumped Swallow Hirundo daurica and Common Magpie Pica pica) were recorded.
1.9
The
tideline transect at the NHS impact monitoring site
recorded higher bird abundance than, and similar species diversity with, the
SPN control site, indicating that shorebird communities were not affected by
the operation of the HK-SWC during the survey.
1.10
A
parametric t-test found statistically significant difference between the bird abundance
along the tidelines at NHS and SPN (P=0.015). As the NHS impact monitoring site is the one
that has higher bird density, the result suggests that the operation of HK-SWC
has no adverse impact on the shorebird communities at NHS during the survey.
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 20 November 2008 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 |
140 |
54 |
5 |
8 |
|
Previous EIA |
23.2 |
58.2 |
1.8 |
2 |
1.12
During this survey, the shorebird density and
diversity at the NHS impact monitoring site were higher than that recorded
during the previous EIA; while the SPN control site recorded similar density
and species diversity with the previous EIA.
The results of
this survey suggest that the operation of HK-SWC had no adverse effect
on the shorebird communities during this survey.
1.13
When compare the recent survey with the previous
survey conducted in September 2008, the densities of shorebirds recorded during
this survey was higher at NHS impact monitoring site (140 birds/ha), but lower
at SPN control site (54 birds/ha) than the previous survey (92 birds/ha at NHS,
136 birds/ha at SPN). For species
richness, the numbers recorded during this survey, five for NHS and eight for
SPN, were about the same as those recorded during the September 2008 survey, three
for NHS and seven for SPN.
Monitoring of Effects of Shade
1.14
During
the survey, only two sets of data, ‘Under Bridge’ and ‘On Exposed Mudflat’,
were collected, as the shade was right under the bridge.
1.15
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 (
dfddfd
1.16
At
the strip of mudflat right under the HK-SWC (Under Bridge), two species (Great Egret Egretta alba and Little Egret Egretta garzetta) of 4 individuals of shorebirds were
recorded during the monitoring survey; whereas one species (Little Egret Egretta garzetta) of five
individuals were recorded on exposed mudflat.
1.17
The
recent monitoring survey show that bird abundance and diversity were similar on
the strips of mudflat “Under Bridge” and “On Exposed Mudflat”. Moreover, a statistical Mann-Whitney Rank Sum
test found no statistically significant difference between the bird abundance
within the two strips of mudflat (P=0.10). This result suggests that the physical
existence of the HK-SWC and its shade has no adverse impact on the shorebird
communities at NHS during the recent survey.
1.18
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