1.1          The intertidal bird surveys were conducted on 21 May 2009.  The weather was sunny.  The temperature was 24.8 oC - 30.9oC and the humidity was 73% - 94%.

 

Intertidal Mudflat Monitoring

 

1.2          Graph 4.1 shows the number and species of shorebirds recorded at the 100 m x 100 m mudflat quadrats at NHS and SPN.

 

Graph 4.1      Abundance and Species Composition of Shorebirds on the Exposed Mudflats (100 m x 100 m Quadrat) at Ngau Hom Shek and Sheung Pak Nai – 21 May 2009

 

1.3              At the NHS and SPN sites, only 1 species, Little Egret Egretta garzetta, was recorded during the survey.  A total of 3 and 4 individuals were recorded at NHS and SPN respectively.  While abundance and species diversity were approximately the same at both sites, 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 21 May 2009 on the Exposed Mudflats (100 m x 100 m 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

3

4

1

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 approximately the same as the numbers recorded during EIA.  There was no evidence to suggest any adverse impacts from SWC operation on shorebird communities during the survey.

1.6          The abundance and diversity of shorebirds recorded at NHS during this survey (1 species of 3 individuals) were lower than the previous monitoring survey conducted in March 2009 (4 species of 28 individuals).   The decrease in abundance is possibly due to the transition from winter period (including March), when large amount of shorebirds aggregate in Deep Bay, to summer period, where all the winter visitors are gone.

 

Tideline Monitoring

 

1.7          Graph 4.2 presents the abundance and species composition of shorebirds recorded on the 500 m x 10 m tideline transects at NHS and SPN.

 

Graph 4.2      Abundance and Species Composition of Shorebirds along the Tidelines (500 m x 10 m transect) at Ngau Hom Shek and Sheung Pak Nai – 21 May 2009

 

 

1.8          At the NHS impact monitoring site, 2 species of 14 individuals of shorebirds (Great Egret Egretta alba, and Little Egret Egretta garzetta) were recorded; whereas at the SPN control site, 3 species of 27 individuals of shorebirds (Little Egret Egretta garzetta,  Great Egret Egretta alba and Green Sandpiper Tringa ochropus) were recorded.

1.9          The tideline transect at the NHS impact monitoring site recorded approximately the same species diversity as, but lower abundance than, the SPN control site.  Although the SPN site recorded higher abundance than the NHS site, nevertheless, a parametric t-test found no statistically significant difference between the bird abundance along the tidelines at NHS and SPN (P=0.148).  The result suggests that no adverse impact on shorebird communities was observed during the operation of the HK-SWC during the survey.

1.10        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 21 May 2009 along the Tidelines (500 m x 10 m 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

28

54

2

3

Previous EIA

23.2

58.2

1.8

2

 

1.11        During this survey, the shorebird density and diversity at the NHS impact monitoring site and SPN control site were approximately the same as that recorded during 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.

1.12        When compare the recent survey with the previous survey conducted in March 2009, the density and species diversity of shorebirds recorded during this survey (28 birds/ha of 2 species) were lower than the previous survey (94 birds/ha of 2 species) at NHS.  While for SPN, this survey also recorded lower abundance than the previous survey in March (this survey – 54 birds/ha of 3 species; previous survey – 110 birds/ha of 5 species).  The decrease in recorded bird abundance is possibly due to the transition from winter period (including March), when large amount of shorebirds aggregate in Deep Bay, to summer period, where all the winter visitors are gone.

 

Monitoring of Effects of Shade

 

1.13        During the survey, only two sets of data, ‘Under Bridge’ and ‘On Exposed Mudflat’, were collected, as the shade was right under the bridge.

1.14        Graph 4.3 presents the results recorded during the survey for effects of shade on the strips of mudflat (250 m x 40 m) at the NHS impact monitoring site.

 

 

 

 

 

 

 

 

 

 

 

Graph 4.3      Abundance and Species Composition of Shorebirds on the Strips of Mudflats (250 m x 40 m) “Under Bridge” and “On Exposed Mudflat” at Ngau Hom Shek – 21 May 2009

              

 

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1.15          At the strip of mudflat right under the HK-SWC (Under Bridge), no shorebird was recorded during the monitoring survey; whereas 1 species (Little Egret Egretta garzetta) of 2 individuals were recorded on the exposed mudflat.

1.16        The recent monitoring survey showed that bird abundance and diversity were not of significant difference between 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=0.690).  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.

1.17        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 50 m 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.