Seasonal and daily migration behavior of Black-necked Cranes (Grus nigricollis) in Yunnan, China: timing and volume

Seasonal and daily migration behavior of Black-necked Cranes Grus nigricollis was observed from October 9, 2006 to May 19, 2007 at Dashanbao National Nature Reserve, NE Yunnan, China. An average of 947 Black-necked Cranes were recorded from November 19, 2006 to March 17, 2007 at the reserve, while a peak number of 1,199 occurred after March 17 during the spring migration period. There were 203 days from the first arrival to the last departure of the Black-necked Cranes, while 90% individuals left for their breeding ground after 153 days. Three numerical peaks of the cranes were detected during autumn and spring migration periods, indicating Dashanbao also served as a staging and stopover site for this species during their migration. The cranes started their spring migration on sunny days with a light breeze, and migration flock sizes were usually larger than 20 individuals. 94.7% of the migrating cranes took off before 13:00, mostly between 10:00 and 11:00. The timing of departure was highly correlated with air temperature at departure initiation－cranes departed earlier with higher temperatures(r= -1.000). When the air temperature was higher, a higher proportion of cranes and bigger flock sizes of the cranes departed. The proportion of the birds departing was mainly correlated with date and weather conditions, indicating that endogenous urging mechanism plays an important role in bird migration.