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.