RAS-1984 — Page 220

RASHKB Journal 皇家亞洲學會香港分會學刊 All AI Reviewed

199

f) Effect of Birds on Productivity

Of the animals listed in trophic level IV, only the wild birds could influence the quantity of economically valuable produce becoming available. Birds have been seen fishing in the kei wai and, on several occasions, startled birds have dropped fish of economic size. Estimates were made for the amount of produce removed by 8 species of birds that have been observed in the kei wais, and the results are given in Table 6.

Species Body wt. (kg.) Population size Period of occurrence (months) Annual Metabolic equivalent Daily rate/bird (kcal day-1) Population intake per bird (kcal year-1) Population intake (kcal) Yellow bittern 0.15 150 7.5 18.11 90.57 2,479,278 Little green heron 0.185 50 2.5 21.17 105.86 969,980 Grey heron 1.500 175 7.3 100.46 502.31 13,384,019 Purple heron 0.900 20 69.70 343.49 752,245 White-breasted waterhen 0.500 150 12 44.36 221.82 12,144,423 Moorhen 0.400 75 12 37.58 187.88 5,143,342 Spotted redshank 0.145 150 6 17.66 88.31 2,417,527 Greenshank 0.180 20 7 20.74 103.72 454,314

Thus, the estimated energy intake by wild birds is approximately 3.77 × 107 kcal. per year. This can be converted to body weight of fish taken by using a value for energy per biomass; in the absence of reliable results for local fish we used a figure of 129 kcal per 100 gm of fish, which is the mean of values for herring, collared herring, haddock, sole and tuna. The corresponding biomass of fish taken by birds at Mai Po is therefore 30,800 kg. per year.

The total area of kei wai No. 7 is about 0.6% of the total area around Hau Hoi Wan (estimated at 16.7 km2) within which the birds might take fish; proportional removal of fish from kei wai No. 7 would be about 18.9 kg. of fishes per annum, which amounts to some 4.5% of the annual produce. This estimate takes no account of the fact that the birds' diets may include significant quantities of worms, amphipods and insects, and must therefore be considered as a maximum figure. Obviously the birds do not compete significantly with man for economic produce.

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199 f) Effect of Birds on Productivity Of the animals listed in trophic level IV, only the wild birds could influence the quantity of economically valuable produce becoming available. Birds have been seen fishing in the kei wai and, on several occasions, startled birds have dropped fish of economic size. Estimates were made for the amount of produce removed by 8 species of birds that have been observed in the kei wais, and the results are given in Table 6. Species Body wt. (kg.) Population size Period of occurrence (months) Annual Metabolic equivalent Daily rate/bird (kcal day-1) Population intake per bird (kcal year-1) Population intake (kcal) Yellow bittern 0.15 150 7.5 18.11 90.57 2,479,278 Little green heron 0.185 50 2.5 21.17 105.86 969,980 Grey heron 1.500 175 7.3 100.46 502.31 13,384,019 Purple heron 0.900 20 69.70 343.49 752,245 White-breasted waterhen 0.500 150 12 44.36 221.82 12,144,423 Moorhen 0.400 75 12 37.58 187.88 5,143,342 Spotted redshank 0.145 150 6 17.66 88.31 2,417,527 Greenshank 0.180 20 7 20.74 103.72 454,314 Thus, the estimated energy intake by wild birds is approximately 3.77 × 107 kcal. per year. This can be converted to body weight of fish taken by using a value for energy per biomass; in the absence of reliable results for local fish we used a figure of 129 kcal per 100 gm of fish, which is the mean of values for herring, collared herring, haddock, sole and tuna. The corresponding biomass of fish taken by birds at Mai Po is therefore 30,800 kg. per year. The total area of kei wai No. 7 is about 0.6% of the total area around Hau Hoi Wan (estimated at 16.7 km2) within which the birds might take fish; proportional removal of fish from kei wai No. 7 would be about 18.9 kg. of fishes per annum, which amounts to some 4.5% of the annual produce. This estimate takes no account of the fact that the birds' diets may include significant quantities of worms, amphipods and insects, and must therefore be considered as a maximum figure. Obviously the birds do not compete significantly with man for economic produce.

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199 f) Effect of Birds on Productivity Of the animals listed in trophic level IV, only the wild birds could influence the quantity of economically valuable produce becoming available, Birds have been seen fishing in the kei wai and, on several occassions, startled birds have dropped fish of economic size. Estimates were made for the amount of produce removed by 8 species of birds that have been observed in the kei wais, and the results are given in Table 6. Table 6. Estimated energy intake by wild birds at Mai Po Species Body wt. Population (kg.) size Period of Annual Metabolic Daily Population occurrence (months) equivalent rate/bird population (kcal day") intake intake per bird (kcal (kcal) year') Yellow bittern 0.15 150 75 18.11 90.57 2,479,278 Little green heron 0.185 50 25 21.17 105.86 969,980 Grey heron 1.500 175 73 100.46 502.31 13,384,019 Purple heron 0.900 20 69.70 343.49 752,245 White breast- ed waterhen 0.500 150 12 150 44.36 221.82 12,144,423 Moorhen 0.400 75 12 75 37.58 187.88 5,143,342 Spotted redshank 0.145 150 6 75 17.66 88.31 2,417,527 Greenshank 0.180 20 7 12 20.74 103.72 454,314 Thus, the estimated energy intake by wild birds is approximately 3.77 × 107 kcal. per year. This can be converted to body weight of fish taken by using a value for energy per biomass; in the absence of reliable results for local fish we used a figure of 129 kcal per 100 gm of fish, which is the mean of values for herring, collared her- ring, haddock, sole and tuna. The corresponding biomass of fish taken by birds at Mai Po is therefore 30,800 kg. per year. The total area of kei wai No. 7 is about 0.6% of the total area around Hau Hoi Wan (estimated at 16.7 km2) within which the birds might take fish, proportional removal of fish from kei wai No. 7 would be about 18.9 kg. of fishes per annum, which amounts to some 4.5% of the annual produce. This estimate takes no ac- count of the fact that the birds' diets may include significant quan- tities of worms, amphipods and insects, and must therefore be considered as a maximum figure. Obviously the birds do not com- pete significantly with man for economic produce.

2026-05-13 02:07:32 · Baseline

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199

f) Effect of Birds on Productivity

Of the animals listed in trophic level IV, only the wild birds could influence the quantity of economically valuable produce becoming available, Birds have been seen fishing in the kei wai and, on several occassions, startled birds have dropped fish of economic size. Estimates were made for the amount of produce removed by 8 species of birds that have been observed in the kei wais, and the results are given in Table 6.

Table 6. Estimated energy intake by wild birds at Mai Po

Species

Body wt. Population

(kg.)

size

Period of

Annual Metabolic Daily Population

occurrence

(months)

equivalent rate/bird population (kcal day")

intake

per bird

(kcal

(kcal)

year')

Yellow bittern

0.15

150

18.11

90.57

2,479,278

Little green

heron

0.185

21.17

105.86

969,980

Grey heron

1.500

175

100.46

502.31 13,384,019

Purple heron

0.900

69.70

343.49

752,245

White breast-

ed waterhen

0.500

150

44.36

221.82

12,144,423

Moorhen

0.400

37.58

187.88

5,143,342

Spotted

redshank

0.145

150

17.66

88.31

2,417,527

Greenshank

0.180

20.74

103.72

454,314

Thus, the estimated energy intake by wild birds is approximately 3.77 × 107 kcal. per year. This can be converted to body weight of fish taken by using a value for energy per biomass; in the absence of reliable results for local fish we used a figure of 129 kcal per 100 gm of fish, which is the mean of values for herring, collared her- ring, haddock, sole and tuna. The corresponding biomass of fish taken by birds at Mai Po is therefore 30,800 kg. per year.

The total area of kei wai No. 7 is about 0.6% of the total area around Hau Hoi Wan (estimated at 16.7 km2) within which the birds might take fish, proportional removal of fish from kei wai No. 7 would be about 18.9 kg. of fishes per annum, which amounts to some 4.5% of the annual produce. This estimate takes no ac- count of the fact that the birds' diets may include significant quan- tities of worms, amphipods and insects, and must therefore be considered as a maximum figure. Obviously the birds do not com- pete significantly with man for economic produce.

RAS-1984 — Page 220

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