ИСТИНА

Individual and sex differences were reported for many bird species, but only a few studies have concentrated on development of such differences in ontogenesis or on comparison of such differences across species. However, it is usually assumed that individual recognition between parents and chicks and sex recognition between conspecifics develops when and where they are needed to restrict parental care to the bird’s own offspring or to protect individuals from mistakes during pair bonding. Here, we tested this hypothesis on three related species of cranes, the Demoiselle (Anthropoides virgo), Red-crowned (Grus japonensis) and Siberian (G. leucogeranus) cranes, that differ in their growth and development rates, vocal characteristics and a few behavioral traits. We analyzed peep calls of 33 captive crane chicks (11 chicks per species, 40 calls per chick), recorded in two Ages (4-45 days and 83-183 days of life) in Oka Crane Breeding Center (Russia). First Age corresponds to period of settled way of life when crane families stay inside their breeding territories; second Age – to period of autumn migration when cranes join in flocks and parents need to recognize their own chick among hundreds of strangers. DFA stepwise analysis showed that vocal indicators of sex were poorly expressed during the first six months of the crane’s life i.e. sexual dimorphism reported for adult crane calls develops later, maybe during sex maturation. However, expression of individual features considerably and significantly increased with fledging and transition to migratory lifestyle. There weren’t any differences in expression of individuality and sex in chick calls of all three species regardless of Age. Interestingly, during the autumn migration, non-linear phenomena percentage increased dramatically in the calls of all three species. We assume that enhancing of individual vocal features expression serves for increasing success of parent-chick recognition in migratory flocks.