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.
韓国忠清南道の天安市郊外に渡来,繁殖するチュウダイサギEgretta alba modestaの渡来相(4月1日~15日),番い形成相(4月16日~22日)及び産卵相(4月23日~3日)における日周活動を1980年と1981年に調査した.1.本種は繁殖地に両年共4月1日から渡来し始めた.その後,多数の群れが訪れ,番い形成相には殆どの個体が定着し,産卵相の終り頃(4月30日)には残留個体数は1980年に737羽,1981年に502羽となった.一方,1981年における繁殖地への定着完了時期は前年よりも4~5日遅く,このことは渡来数ピーク時の直前における平均気温が1981年には約6℃低かったことと関連するようである.2.雨天や曇天における飛来時刻は晴天に比して約1時間も早く,特に雨天では出入個体数が少なかった.このことは本種の日周活動が照度と晴雨に大きく影響されることを示唆する.3.繁殖地における本種の出入方向は,より良好な餌場の方向に集中し,周辺の環境立地条件,特に餌場条件に強く支配されることが知られた.