Variability of specific structures Tree Pipit

Primary function of birdsong is for territorial defense or attraction of females. Birdsong also contains much more other information and can be used to inform males and females about quality of singing bird. It was demonstrated, that for different bird species condition of male correlates with what structures of birdsong are produced. More complex structures are produced by superior males. Females of some species prefer males with ability to produce more complex structures. This work deals with structures of singing of the tree pipit species (Anthus trivialis). These structures are also known as trills. It is assumed, that trills may contain some information about quality of male, which can be evaluated by males and females. Birdsong of tree pipit contains two types of trills - loud and soft. Loud trills are used in aggressive interactions between two males. Soft trills are not used in aggresive context and they differ in consistency - regularity, that can be expressed as tempo of trill. When measuring tempo of trills for every tree pipit male, the tempo is different among males and also correlates with their ability to maintain stable territory over the entire nestling season. Males with faster (more consistent) tempo of trill had stable territory, while males with slower (irregular) tempo of..