Results and observation

1.1 The intertidal bird surveys were conducted on 7 March 2008. It was sunny and the sky was cloudy. The temperature was about 22^oC.

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 – 7 March 2008

1.3 At the NHS impact monitoring site, three species (Great Egret Egretta alba, Little Egret Egretta garzetta, Cattle Egret Bubulcus ibis) of eight individuals of birds were recorded; whereas at the SPN control site, three species (Little Egret Egretta garzetta, Osprey Pandion haliaetus and Eurasian Curlew Numenius arquata) of four individuals of birds were recorded.

1.4 The NHS impact site recorded two times the abundance of birds than the SPN control site; and the numbers of species at both sites were the same. There is no significant evidence which shows that adverse impact on bird communities was caused during 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 7 March 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	8	4	3	3
Previous EIA	2.3	4.2	1.3	1.8

1.6 The shorebird densities and species richness at NHS and SPN recorded during this survey were same as / higher 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 densities of shorebirds recorded during this survey were lower than the previous monitoring survey conducted in January 2008. In the previous survey, there were 19 birds/ha and 9 birds/ha at NHS and SPN respectively. During this survey, there were 8 birds/ha and 4 birds/ha at NHS and SPN respectively. The decrease in numbers could be explained by the approaching of the end of winter migration period, resulting in the departure of passage migrants and winter visitors in Hong Kong.

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 – 7 March 2008

1.9 At the NHS impact monitoring site, two species (Great Egret Egretta alba and Little Egret Egretta garzetta) of 18 individuals of shorebirds were recorded; whereas at the SPN control site, three species (Little Egret Egretta garzetta, Cattle Egret Bubulcus ibis and Eurasian Curlew Numenius arquata) of 12 individuals of shorebirds were recorded.

1.10 The tideline transect at the NHS impact site recorded a higher number of shorebird abundance than the SPN control site, and the species diversity is approximately the same for both sites (2 for NHS, 3 for SPN). There is no indication that shorebird abundance was affected by the operation of the HK-SWC.

1.11 A Mann-Whitney Rank Sum test found no statistically significant difference between the bird abundance along the tidelines at NHS and SPN (P=0.120). This further supports that the operation of HK-SWC had no impact on the shorebirds 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 7 March 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	36	24	2	3
Previous EIA	23.2	58.2	1.8	2

1.13 The shorebird densities and species richness at the NHS impact site were both higher than the numbers 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 lower than the previous survey conducted in January 2008. In the previous survey, there were 86 birds/ha and 64 birds/ha at NHS and SPN respectively; during this survey, there were 36 birds/ha and 24 birds/ha at NHS and SPN. For species richness, the numbers recorded during this survey (2 for NHS and 3 for SPN) were also lower than those recorded in January 2008 (6 for NHS and 9 for SPN). The decrease in shorebird abundance and species richness may be due to the departure of passage migrants and winter visitors in Deep Bay area towards the end of winter migration period.

Monitoring of Effects of Shade

1.15 During the survey, the sky was overcast with clouds and the shade of HK-SWC was not right underneath the bridge. As a result, 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 (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 – 7 March 2008

1.17 At the strip of ‘Exposed Mudflat’, two species (Little Egret Egretta garzetta and Great Egret Egretta alba) of nine individuals were recorded, whereas one species of four and three individuals were recorded on the strips ‘Under Bridge’ and ‘In Shade’ respectively. These results show that species abundance and richness on the surveyed area right under the HK-SWC and in shade were lower than that on exposed mudflat, suggesting that the operation of HK-SWC may have potential impacts on the distribution of shorebird community.

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 one-way ANOVA test found no statistically significant difference between the bird abundance within the strips ‘In shade’, ‘Under Bridge’ and on ‘Exposed Mudflat’ (P=0.267). 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. No trigger / action level exceedance was recorded in the survey.