Breeding Ecology of the Eastern Great White Egret, Egretta alba modesta, in Korea : I. Diurnal Activity in the Breeding Season

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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 : I.繁殖季節における日周活動
  • 韓国産チュウダイサギEgretta alba modestaの繁殖生態に関する研究-1-繁殖季節における日周活動
  • カンコクサン チュウダイサギEgretta alba modesta ノ ハン

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Abstract

Diurnal activity of the Eastern Great White Egret, Egretta alba modesta, in the advertising (1 to 15 April), pairing (16 to 22 April) and egg-laying (23 to 30 April) phases was investigated at a suburb of Cheonan City, Chungcheongnamdo, Korea, from 27 March to 30 April in 1980 and 1981. 1. The first inward migration of the egret was made on 1 April in both years. Prior to a settlement of most individuals in the pairing phase, large numbers continued to arrive at the breeding site, and then 732 individuals in 1980 and 502 in 1981 remained at the site in the late egg-laying phase (30 April). On the other hand, the complete settlement time was delayed by 4-5 days in 1981 compared with that in 1980; the delay seems to be associated with an average ambient temperature immediately before the arrival peak in 1981, which was lower by about 6℃ than that in 1980. 2. The egret returned to the roost about 1 hour earlier on ralny or cloudy days than on fine days. Particularly, the number of arriving and/or returning, and departing individuals was fewer on rainy days than on other days. These phenomena suggest that the diurnal activity of the egret is strongly affected by the light and darkness, and weather (rain or shine). 3. It is revealed that the departure-arrival directions of the egret at the breeding site are concentrated in the directions of better feeding sites, and that the fight directions are controlled by the topography of the environments, especially conditions of the feeding site.

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