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The main objectives of this study were to provide a thorough description of the advertising song in the male pied flycatcher Ficedula hypoleuca and examine the complexity of the song and its variability within and between breeding seasons by qualitative and quantitative analyses of its structure.Songs were recorded from 117 males in central Norway in one or more of the three stages of the breeding season: before pairing, during nest building, and in the laying/brooding stage. Eight males were recorded both before and after pairing, and 13 males were recorded in two consecutive years. Spectrographic analyses were based on 25 consecutive song strophes per male.When the males became mated their song changed in a number of ways: in addition to reduced singing activity, the n urn her of figures and figure types in the song strophe became fewer at the same time as the song strophe became shorter. There was also a tendency towards increasing song versatility and decreasing repertoire size. Individual males differed significantly in all tested variables, as did the two categories unpaired and paired males.From one year to the next the song of the male pied flycatchers became more versatile, the number of unique figures increased and there was a tendency towards increasing repertoire size. Changes in the other song variables were insiginificant, although considerable individual variations were recorded. New song figure types and song types appeared between years in individual males of any age. This may indicate that song learning continues into adulthood, or that subsets of early memorized songs are used in different years.

Observations and experiments were made on the ability of reindeer mothers and calves to identify each other by voice. Field observations showed that this ability is very well-developed and that discrimination is very good due to high individuality of the voices. Playback experiments with recorded sounds confirmed the field observations.