Observations on Daurian Jackdaws (Corvus dauurica)were carried during four consecutive migratory and wintering seasons of 2005 to 2009 at Milu park,Beijing.We recorded population size variation,flock size,and percentage of juveniles.Daurian Jackdaws were observed 166±11 days from mid October to the end of the following May.The population size reached peaks in late October or early November.No significant yearly difference in population size among four seasons (χ²₍₃₎ =6.14 P=0.11>0.05)was identified by Krushkal-wallis H test,but the peak number of birds (6 500±300) recorded in 2008 was significantly different from the other three seasons (χ²₍₃₎=8 484.47,P<0.01).Juveniles arrived at the study area earlier and left later than adults,as result,the proportion of juveniles in the population was higher in October and May each year,and even reached to 100% in the beginning and ending of migratory and wintering seasons.Seeking water resource after forage in refuse dump around Milu Park would be the main reason for them forming flocks.