Results and observation

1.1               The intertidal bird surveys were conducted on 11 September 2008.  The weather was fine and sunny.  The temperature was between 26-32oC and the humidity was between 65-82%.

 

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 – 11 September 2008

1.3              At the NHS impact monitoring site, two species (Little Egret Egretta alba and Great Egret Egretta alba) of 11 individuals of birds were recorded; whereas at the SPN control site, five species (Little Egret Egretta alba, Chinese Pond Heron Ardeola bacchus, Green Sandpiper Tringa ochropus, Eurasian Curlew Numenius arquata, and Little Ringed Plover Charadrius dubius) of 18 individuals of birds were recorded.  As the abundance and diversity at NHS and SPN were similar, there is no strong evidence to suggest any adverse impacts from SWC operation on shorebird communities.

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 11 September 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

18

2

5

Previous EIA

2.3

4.2

1.3

1.8

 

1.5               The shorebird density and diversity at NHS and SPN recorded during this survey were both 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 density of shorebirds recorded at NHS during this survey was slightly higher than the previous monitoring survey conducted in July 2008 (2 in NHS and 8 in SPN), whilst the densities recorded during the recent surveys (September, July and May 2008) were lower than those recorded in winter months (November 2007 and 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 500m x 10m tideline transects at NHS and SPN.

Graph 4.2      Abundance and Species Composition of Shorebirds along the Tidelines (500m x 10m transect) at Ngau Hom Shek and Sheung Pak Nai – 11 September 2008

1.8               At the NHS impact monitoring site, three species of 46 individuals of shorebirds (Great Egret Egretta alba, Little Egret Egretta garzetta and White-breasted Kingfisher Halcyon smyrnensis) were recorded; whereas at the SPN control site, seven species of 68 individuals of shorebirds (Great Egret Egretta alba, Little Egret Egretta garzetta, Chinese Pond Heron Ardeola bacchus, Euraisan Curlew Numenius arquata, Common Ringed Plover Charadrius hiaticula, Common Sandpiper Actitis hypoleucos, and Green Sandpiper Tringa ochropus) were recorded.

1.9               The tideline transect at the NHS impact site recorded lower number of bird abundance and diversity than the SPN control site, indicating that shorebird communities may be affected by the operation of the HK-SWC.

1.10           Nevertheless, a parametric t-test found no statistically significant difference between the bird abundance along the tidelines at NHS and SPN (P=0.187).  This supports that the operation of HK-SWC has no 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 11 September 2008 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

92

136

3

7

Previous EIA

23.2

58.2

1.8

2

 

1.12           The shorebird density and diversity at the NHS and SPN monitoring sites recorded during this survey were both higher than that recorded during the previous 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 densities of shorebirds at NHS and SPN recorded during this survey were higher than the previous survey conducted in July 2008.  In the previous survey, there were 48 birds/ha and 40 birds/ha at NHS and SPN respectively; during this survey, there were 92 birds/ha and 136 birds/ha at NHS and SPN.  For species richness, the numbers recorded during this survey, three for NHS and seven for SPN, were about the same as those recorded in the July 2008 survey, five for NHS and four 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 (250m x 40m) at the NHS impact monitoring site.

Graph 4.3      Abundance and Species Composition of Shorebirds on the Strips of Mudflats (250m x 40m) “Under Bridge” and “On Exposed Mudflat” at Ngau Hom Shek – 11 September 2008

 

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1.16           At the strip of mudflat right under the HK-SWC (Under Bridge), no bird was recorded during the monitoring survey; whereas two species (Great Egret Egretta alba and Little Egret Egretta garzetta) of seven individuals were recorded on exposed mudflat 

1.17           The recent monitoring survey show that bird abundance and diversity “Under Bridge” were lower than that “On Exposed Mudflat”.  However, a parametric t-test found no statistically significant difference between the bird abundance within the mudflats ‘Under Bridge’ and ‘On Exposed Mudflat’ (P=0.147).  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 50m away from both sides of the alignment of HK-SWC.  The oyster areas were observed to be a popular feeding ground for shorebirds and were frequently visited.  The abundant food resource in these areas may have a positive effect on the abundance and diversity of intertidal shorebirds on the strip of exposed mudflat at NHS.