World population
World population survey was completed in 2014 both in Russia and China, the number for North Korea was estimated without survey there. Surveys on dispersal wintering grounds are useless and the way to estimate world population is to survey pristine rivers within breeding range. Rivers of Central China, primarily tributaries of Yangtze River, and all rivers of South Korea constitutes the wintering area well known nowadays. Habitat loss in China led to breeding range reduction and fragmentation there. In Russia population seems to stabilize in 1900th and until now.