ИСТИНА

Birdsong is a highly complex signaling system which can theoretically convey an immense amount of information via its (1) song type/note composition and (2) ordering rules. Besides, birdsong is a good example of non-random vocal structures in nonhuman animals. Non-random vocal structures are well known in birds, but in most cases we know neither what the content of these signals are nor if conspecifics could use and encode information in them. We asked whether organization of song bouts functions as a graded signal of aggression in Claudia' Leaf warblers. The study was conducted in April-June 2016 in Hupingshan National Nature Reserve (Hunan province, China). We simulated territorial intrusion by broadcasting Claudia' Leaf warbler song in territories. Experiments involved 14 different males. Comparing singing prior, with those produced in response to playback, showed that (1) observed repertoire size increased, (2) first-order relative entropy decreased (i.e. non-randomness of singing increased) and (3) singing rate increased. Additionally we found that soft low-amplitude songs were produced in response to playback by several (but not all) males. This study thus provides empirical evidence that non-random vocal structures along with the other parameters could play a role in male-male competition.