Results and observation

1.1               The intertidal bird surveys were conducted on 15 January 2008.  The sky was overcast and it was windy.  The temperature was about 13oC and the humidity was about 65%.

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 – 15 January 2008

 

1.3               At the NHS impact monitoring site, four species (Great Egret Egretta alba, Little Egret Egretta garzetta, Common Sandpiper Actitis hypoleucos and Grey Heron Ardea cinerea) of 19 individuals of birds were recorded; whereas at the SPN control site, six species (Little Egret Egretta garzetta, Grey Heron Ardea cinerea, Little Ringed Plover Charadrius dubius, Black-capped Kingfisher Halcyon pileata, White-breasted Kingfisher Halcyon smyrnensis and White Wagtail Motacilla alba) of nine individuals of birds were recorded. 

1.4               The NHS impact site recorded more than two times the abundance of birds than the SPN control site.  This is an indication that no adverse impact on bird communities was caused during the operation of the HK-SWC.  Even though two less species were recorded at the NHS impact site, the difference of species number between the two monitoring sites is not significant enough to suggest an adverse impact on species richness from the bridge.

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 15 January 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

19

9

4

6

Previous EIA

2.3

4.2

1.3

1.8

 

1.6               The shorebird densities and the number of shorebird species at NHS and SPN recorded during this survey were both higher than the numbers recording during EIA.  The results of this survey suggest that the operation of HK-SWC had no effect on the shorebird communities.

1.7               The densities of shorebirds recorded during this survey were very similar to the previous monitoring survey conducted in November 2007.  In the previous survey, there were 14 birds/ha and 12 birds/ha at NHS and SPN respectively. During this survey, there were 19 birds/ha and 9 birds/ha at NHS and SPN respectively.  The densities recorded in the recent surveys (November 2007 and January 2008) are comparatively higher than the figures recorded in July (3 birds/ha and 5 birds/ha) and September (2 birds/ha and 9 birds/ha) 2007.  It should be noted that November 2007 and January 2008 lie within the winter migration period; arrivals of population of passage migrants and winter visitors in local areas could have led to the increase in bird numbers during the recent surveys.

 

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 – 15 January 2008

 

1.9               At the NHS impact monitoring site, six species of 43 individuals of shorebirds (Great Egret Egretta alba, Little Egret Egretta garzetta, Common Sandpiper Actitis hypoleucos, Grey Heron Ardea cinerea, Eurasian Curlew Numenius arquata and Black-faced Spoonbill Platalea minor) were recorded; whereas at the SPN control site, nine species of 32 individuals of shorebirds (Great Egret Egretta alba, Little Egret Egretta garzetta, Chinese Pond Heron Ardeola bacchus, Common Sandpiper Actitis hypoleucos, Grey Heron Ardea cinerea, Eurasian Curlew Numenius arquata, Black-capped Kingfisher Halcyon pileata, White-breasted Kingfisher Halcyon smyrnensis and Little Ringed Plover Charadrius dubius) were recorded.

1.10           The tideline transect at the NHS impact site recorded a higher number of shorebird abundance than the SPN control site, indicating that shorebird abundance is not adversely affected by the operation of the HK-SWC, although three less species was recorded from NHS impact monitoring site when compared with the SPN control site.

1.11           A parametric t-test found no statistically significant difference between the bird abundance along the tidelines at NHS and SPN (P=0.392).  This further supports that the operation of HK-SWC has 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 15 January 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

86

64

6

9

Previous EIA

23.2

58.2

1.8

2

1.13           The shorebird densities and species richness at NHS and SPN recorded during this survey 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 similar to the previous survey conducted in November 2007.  In the previous survey, there were 78 birds/ha and 72 birds/ha at NHS and SPN respectively; during this survey, there were 86 birds/ha and 64 birds/ha at NHS and SPN.  For species richness, the numbers recorded during this survey, six for NHS and nine for SPN, were higher than those recorded in the November survey (five for NHS and six for SPN).   Arrival of passage migrants and winter visitors in Deep Bay in winter season may result in the increase of species abundance and richness recorded in this survey.

 

Monitoring of Effects of Shade

 

1.15           During the survey, the sky was overcast with clouds and there was a shade right under the HK-SWC bridge on the mudflat.  As a result, two sets of data, ‘In Shade / Under Bridge’ and ‘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) “In Shade / Under Bridge” and on “Exposed Mudflat” at Ngau Hom Shek – 15 January 2008

 

1.17           At the strip of mudflat right under HK-SWC (In Shade / Under Bridge), a species (Little Egret Egretta garzetta) of three individuals were recorded; whereas four species (Little Egret Egretta garzetta, Grey Heron Ardea cinerea, Magpie Robin Copsychus saularis and White-breasted Kingfisher Halcyon smyrnensis) of eight individuals were recorded at the strip on the exposed mudflat.  The recent monitoring survey shows that species abundance and richness on the surveyed area under the HK-SWC in shade were lower than that on exposed mudflat, suggesting that the operation of the HK-SWC may have potential impacts on the distribution of shorebird community.

1.18           As discussed in the monitoring report for 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 the population is not randomly distributed, which may cause bias in statistical analysis.

l            Arrival of large population of winter visitors in winter season may amplify the difference in shorebird abundance between the strips under the bridge and on the exposed mudflat recorded in the lately surveys.

1.19           It should also be taken into account that during the recent survey, mudflat area with oyster succession were found located 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. 

1.20           Nevertheless, parametric t-test found no statistically significant difference between the bird abundance within the strips of ‘In shade / Under Bridge’ and ‘Exposed Mudflat’ (P=0.161).  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.