Results and observation

1.1               The intertidal bird surveys were conducted on 6 May 2008.  The weather was fine but cloudy. The temperature was about 25oC and humidity was 81%.

 

Intertidal Mudflat Monitoring

 

1.2               Graph 4.1 shows the abundance 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 – 6 May 2008

 

 

 

1.3               At the NHS impact monitoring site, two species (Great Egret Egretta alba and Little Egret Egretta garzetta) of three individuals of birds were recorded; whereas at the SPN control site, one species (Little Egret Egretta garzetta) of two individuals of birds were recorded.

1.4               The shorebird density and species richness at the NHS impact monitoring site is slightly higher than the SPN control site.  There is no significant evidence to suggest that adverse impact on bird communities was caused during the operation of 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 6 May 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

3

2

2

1

Previous EIA

2.3

4.2

1.3

1.8

 

1.6               The shorebird density and species richness at NHS was slightly higher than that recorded during EIA; whereas the density recorded at SPN was slightly lower than that recorded during EIA.  These results suggest that the operation of the HK-SWC had no effect on the shorebird communities during this survey.

1.7               The density of shorebirds recorded during this survey was similar to the previous findings from monitoring survey conducted in March 2008.  In the previous survey, there were 8 birds/ha and 4 birds/ha at NHS and SPN respectively; while 3 birds/ha and 2 birds/ha were recorded at NHS and SPN during the recent survey. 

 

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 (500m x 10m transect) at Ngau Hom Shek and Sheung Pak Nai – 6 May 2008

 

1.9               At the NHS impact monitoring site, six species (Great Egret Egretta alba, Little Egret Egretta garzetta, Chinese Pond Heron Ardeola bacchus, Black-crowned Night Heron Nycticorax nycticorax, Green Sandpiper Tringa ochropus and Terek Sandpiper Xenus cinereus) of 35 individuals of shorebirds  were recorded; whereas at the SPN control site, six species (Great Egret Egretta alba, Little Egret Egretta garzetta, Chinese Pond Heron Ardeola bacchus, White-breasted Kingfisher Halcyon smyrnensis, Wood Sandpiper Tringa glareola and Green Sandpiper Tringa ochropus) of 32 individuals of shorebirds  were recorded.

1.10           The tideline transects at NHS and SPN recorded the same level of species richness (six species), and that shorebird abundance is approximately the same for both sites (35 for NHS, 32 for SPN).  There are no indications that shorebird abundance was affected by the operation of the HK-SWC.

1.11           A statistical t-test found no statistically significant difference between the bird abundance along the tidelines at NHS and SPN (P=0.857).  This further supports that the operation of HK-SWC had no impact on the shorebird communities at the NHS monitoring site 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 6 May 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

70

64

6

6

Previous EIA

23.2

58.2

1.8

2

 

1.13           The shorebird density and species richness at both of the NHS and SPN sites were higher than the values recorded during EIA.  The results of this survey suggest that the operation of HK-SWC had no effect on the shorebird communities during this survey.

1.14           The densities of shorebirds at NHS and SPN were higher than the previous survey conducted in March 2008.  In the previous survey, there were 36 birds/ha and 24 birds/ha at NHS and SPN respectively; during this survey, there were 70 birds/ha and 64 birds/ha at NHS and SPN.  For species richness, the numbers recorded during this survey (6 for NHS and 6 for SPN) were also higher than those recorded in March 2008 (2 for NHS and 3 for SPN).  The increase in numbers during this survey could be due to the influx of spring passages and migrants to Hong Kong from other regional areas during the survey period.

 

Monitoring of Effects of Shade

 

1.15           During the survey, the weather was fine but the sky was cloudy.  The shade of HK-SWC was right underneath itself.  As a result, only two 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 (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 / In Shade” and “On Exposed Mudflat” at Ngau Hom Shek – 6 May 2008

 

 

1.17           At the strip of ‘Exposed Mudflat’, two species (Little Egret Egretta garzetta and White-breasted Kingfisher Halcyon smyrnensis) of two individuals were recorded, whereas no shorebird was recorded on the strip ‘Under Bridge / In Shade’.  

1.18           As discussed in the operation monitoring report dated November 2007 and January 2008, distribution of shorebirds may be affected by a number of abiotic and biotic factors other than the operation of the HK-SWC, and they are listed in the following:

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 the population is not randomly distributed, which 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.

1.19           Nevertheless, the statistical Mann-Whitney Rank sum test found no statistically significant difference between the bird abundance within the strips ‘Under Bridge / In Shade’ and ’On Exposed 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.