Ecological Study on Wintering Night-Herons (Nycticorax nycticorax) in Shanghai

About 1 500 wintering nigh-herons were stu died during December 1983-May 1994 and December 1998-May 1999 in Shanghai.The results were as the follows:1) The population of birds was 1.531±273,ratio of juv./adult 1.731∶1±0.035.Most of the adults migrate to the north during the middle of March-end of April and the juveniles migrate in the middle of April-middle of May (Fig.1).2) Luminosity is the main factor for regulating the birds daily time budget,however,the birds tend to leave from roosting area earlier and come back later as the night time becomes longer and day time becomes shorter (Figs.2,3,4).3) The distribution pattern of the night-herons at roosting area are variable in different periods:uniform distribution in middle of winter when the bird number is at its peak,but aggregation at the migrant period when bird number drops (Table 1).The result strongly indicates the possibility that night-herons have fixed roosting sites in winter (Table 2).4) The wind is the most important factor affecting the birdss distribution.Other climate factors have no much influence on it (Tables 3,4;Fig.5).