Breeding Ecology of the Eastern Great White Egret, Egretta alba modesta, in Korea : II. Nest Building Behavior and Protection Procedure

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  • 韓国産チュウダイサギEgretta alba modestaの繁殖生態に関する研究 : II.造巣習性と保護･管理対策
  • 韓国産チュウダイサギEgretta alba modestaの繁殖生態に関する研究-2-造巣習性と保護・管理対策
  • カンコクサン チュウダイサギEgretta alba modesta ノ ハン

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Abstract

Nest building behavior of the Eastern Great White Egret, Egretta alba modesta, was investigated at a suburb of Cheonan City, Chungcheongnamdo, Korea, from 27 March to 31 July 1981 and 3 April 1984. 1. All the egrets nested on the Japanese larch, Larix leptolepis, at 4.6 to 8.7 m (6.1 m on an average) above the ground. 2. One to four nests were built (1.9 on the average) per tree; nest materials were brought chiefly by males (94.4%), while the nest building was carried out almost entirely by females. 3. One nest consisted of 156-282 sticks (212 ones on an average) of such tree species as the Japanese larch (47.4%), the locust, Robinia pseudo-acacia (35.8%), the Japanese red pine, Pinus densiflora (8.5%), the Japanese alder, Alnus japonica (5.7%) and the red oak, Quercus acutissima (2.6%). 4. The Japanese larch showed a much larger annual increment in height than in diameter at breast height (DBH), thus it tended to lose its stability against a strong wind; as a result, most of the nests and eggs fell from the trees. From this fact, the Japanese larch does not seem suitable for the egrets as nesting trees, and this might be the greatest reason for their abandonment of the breeding site. 5. As a protection procedure for the egret, first of all, it is necessary to plant both the Japanese red pine with a low growth rate, but having a thick trunk, stability against a strong wind and power of resistance to the damage caused by their droppings, and the locust with a high growth rate as a stopgap for about 40 years until the planted red pines become suitable for the egret's nesting, in and around the breeding site. And then a strict enforcement of the drastic prohibition of hunting, stealing their egg and invasions into the breeding site by people is demanded. Also, the application of BHC and DDT in Southeast Asia should be restrained.

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