From October 2004 to May 2005, flock size and composition of wintering black-necked cranes ( Grus nigricollis
) were studied using spot scanning technique at Napahai Nature Reserve in Yunnan province. At night, the mean wintering population size was 67.9 (16-157, n=
17). Composed by common crane ( Grus grus
) or not, roost cranes were divided into sing-species flock and mixed-species flock. The numbers of crane in sing-species flock were 65.3% of total black-necked cranes. In the day, feeding flocks were classified into three types: family group comprised of breeding pair and their offspring ranging between two to four; sub-adult flock composed mainly by sub-adults ranging between three to 65 with an average size of 16.1(n=
1017); special flock composed by single cranes. Black-necked crane flocks were affected by season, temperature, breeding status, food abundance and availability, and their sizes changed significantly in daytime or between different months (P
=0.000<0.05). After family breakup happened in late March, Juveniles were drove away by their parents and then they got together to join the sub-adult flocks.