| Budget Amount *help |
¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1991: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1990: ¥700,000 (Direct Cost: ¥700,000)
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| Research Abstract |
To investigate the feeding ecology of the Shovelers (Anas clypeata) wintering in the hypertrophic Lake Teganuma, field survey and anatomical analysis were conducted as follows ; 1) temporal fluctuation of the number, horizontal distribution and frequency of feeding behavior of the Shovelers both in day and night were observed, and the results were compared to those of the other 5 dabbling duck species common in the lake during winter, 2) diurnal fluctuation of feeding activity of the Shovelers was observed, and 3) temporal and horizontal fluctuations of zooplankton biomass was surveyed, during October to May, 1989-1991.4) measurements of lamellae distance was made on bills of 16 Shovelers captured, and threshold size of zooplankton for the ducks was estimated. Throughout the observations period feeding activity of the Shovelers was most highest among the 6 dabbling ducks (Mallard, Spot-billed duck, Green-wiged Teal, Pintail and Gadwall). The results during 1989-1990 suggested that the number of Shovelers increased during February-March and tended to gather north-eastern area in the lake, and the increased birds foraged actively at the water surface both in day and night. The temporal and horizontal fluctuations of possibly edible sized zooplankters (Cyclopoids) showed similar patterns as those of the ducks. However, during 1990-1991, the total and foraging individuals of the Shovelers decreased compared to the first season and critical distribution pattern was not observed. Zooplankton biomass did not increase either. The results suggested that fluctuation of the number, distribution pattern and foraging activity of the Shovelers corresponded to the temporal and horizontal fluctuation of zooplankton biomass. Threshold size of zooplankton for Shovelers was estimated to be 400mum. The size corresponded to that of cyclopoids which affected the Shovelers' utilization pattern of the lake.
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