All R428 individuals received a metallic-numbered ring when first caught while sleeping in nest boxes or when handled as nestlings. Adult birds were also given a combination of three colour rings to allow individual identification in the field. Hence, the identity of all individuals was known before the recordings and the playback experiment were carried out. As age was included to control the statistical analysis, we determined exact age using birth records for all resident birds. Age of immigrant birds was determined based on colour differences of primary coverts, grey for yearlings and bluish for older birds. Exact age could not be determined for four individuals that arrived as adults, so their age was not included in the analysis. Great tit males sing year-round, but singing activity increases during the breeding season and it is highly related to female fertility. Males display a peak of uninterrupted singing activity in the surroundings of the nest before sunrise during the reproductive period, known as the dawn chorus, which is thought to have a function for territorial defence, mate guarding, and female attraction. Both for the playback experiment and the longitudinal analysis, we recorded the complete dawn chorus of great tit males during the egg-laying period of their females and at the earliest when the second egg was laid. Dawn choruses were recorded between 5:00 and 7:20 am and the person responsible for the recording was always present before the male started singing up until the dawn chorus ended. Following previous studies, we considered the end of the dawn chorus to be when the female emerged from the nest and engaged in copulation behaviour with the male. Great tit males have a repertoire ranging from 1 to up to 9 different discrete units or phrase types, also referred to as song types that can be recognized unambiguously. Song types are repeated in a stereotypic way during 1 to 5 seconds which is referred as a strophe, and usually several strophes of the same song type are sung before another song type is introduced . For all individuals, we identified all the different song types that were sung during each dawn chorus and constructed a library to establish repertoire size and to compare repertoire composition. Two different observers independently inspected a subsample of the dawn choruses of the same males from 2008 with the aim of estimating repeatability of the assessment of repertoire size using analysis of variance. We performed a playback experiment and a longitudinal analysis to replicate previous studies on song repertoire flexibility in the great tit. In contrast to earlier research our results appear to indicate that repertoire size and composition are highly repeatable in the great tit within a breeding season after confrontation with a novel song, and also between years. Our findings, therefore, suggest a very limited repertoire flexibility in our population of the species under study.