2.1 Study species
Black-necked cranes are a vulnerable species in the IUCN Red List,
endemic to the western plateaus of China (including the Qinghai-Tibet
and Yunnan-Guizhou Plateau) with less than 5% population inhabited in
wetlands of Bhutan and India (Li, 2014). Breeding pairs occupy relative
constant territories while nonbreeding sub-adults wander across vast
areas in flocks (Zhang et al., 2017); they aggregate into flocks or in
small family groups in winter (Liu et al., 2008). Family groups usually
consist of parents and 0, 1 or 2 juveniles. It is easy to distinguish
juveniles from adults from blocky brownish feathers, smaller body size
and whistles like calls. While adults have a distinct black neck, flight
feathers and tail compared with white plumages. However, telling males
from females apart is hardly achieved except from appearance of unison
call.