Abstract:Poyang Lake is the largest freshwater lake in China, and many waterbirds, including four endangered crane species, overwinter at this lake each year. Feeding and resting are the behaviors primarily exhibited by the wintering waterbirds, that Poyang Lake provides good food and rest resources for them. However, no comprehensive data about the wintering ecology of these crane species exists. From October 2014 to April 2015, we investigated the group sizes and adult-juvenile compositions of the Siberian crane (Grus leucogeranus), hooded crane (G. monacha), white-naped crane (G. vipio), and common crane (G. grus) at 45 survey sites on Poyang Lake using the point count method. The results showed that the mean group sizes of the four crane species were (23.86±10.26) for the Siberian crane (group number N=104), (6.09±2.55) for the hooded crane (N=98), (6.09±2.55) for the white-naped crane (N=105), and (5.55±1.26) for the common crane (N=246). Crane group size in Poyang Lake did not conform to predictions based on their vigilance behavior. However, habitat quality may explain this discrepancy. The group size of hooded cranes at the mid-winter stage was significantly smaller than during the late winter stage, whereas other cranes showed no significant differences between the three wintering stages. The common crane group size also showed no significant differences between regions. The four species of cranes most frequently appeared in groups of 1-5 individuals. Most Siberian crane individuals appeared in groups of 35 individuals or more, whereas other cranes were in groups of 1-5, or more than 35 individuals. The Siberian crane (64.29%, total group number N=98), hooded crane (71.91%, N=89), white-naped crane (70.77%, N=65), and common crane (63.11%, N=206) appeared mainly in family groups, suggesting that ensuring an adequate supply of food was more important than increasing foraging time. The highest percentage of Siberian crane family group types was two adults with one offspring (65.08%), whilst two adults predominated in the hooded crane (51.56%), white-naped crane (52.17%), and common crane (47.69%) populations. The lower percentage of family types with two adults and two offspring indicated that Siberian crane families found it more difficult than the families of the other three cranes to raise two offspring at the same time. The percentage of juvenile Siberian cranes was 12.27% (individual number N=1695), 14.42% (N=416) for the hooded crane, 16.59% (N=229) for the white-naped crane, and 20.46% (N=655) for the common crane. There was no significant difference in the percentage of juveniles over the three wintering stages for any of the crane species. Duchang Provincial Migratory Birds Nature Reserve and East Poyang Lake National Wetland Park were found to contain significantly and extremely significantly (χ2=6.495, P=0.011 and χ2=9.012, P=0.003, respectively) more common cranes (25.25% and 25.14%, respectively) than Poyang Lake National Nature Reserve (14.24%). The percentage of juvenile Siberian cranes remained low in Poyang Lake, whereas that of the hooded cranes significantly decreased between 2014 and 2015 from the corresponding percentage of the population in 2012-13. The population of common cranes and white-naped cranes remained stable or increased, which suggested that Poyang Lake is able to maintain and develop healthy populations of these cranes.