Bird song is used for both intra-sexual and inter-sexual interactions, in male-male competition and for attracting females. In species that use song for attraction, the females often prefer males with larger repertoires and more complex songs. This would be beneficial for the females if the song is an honest signal of the males’ quality. If so a female that chooses a male with a complex song may gain benefits such as good territory quality, good parental care or good genes. The song repertoire of several passerine birds have been found to correlate with age, and some have found correlations between the song repertoire and male qualities like body mass, wing and tarsus length, plumage colour and arrival date. These have also been found to correlate with the song repertoire and song versatility in the pied flycatcher Ficedula hypoleuca in a population, and correlation between song and age has been found in individual pied flycatchers. Delayed maturation in song and other traits such as colour, length, and body mass would also suggest a correlation between these variables and song. There are also external factors that may affect the song of the pied flycatcher. The temperature and precipitation have been seen to affect the males singing rate, and the number of males that are close by might suggest how many possible song tutors there are available and how much song a male is able to hear and learn. I studied the song repertoire and song versatility of 10 long-lived male pied flycatchers, to see if there was a correlation between the song and male qualities and to see if the song was affected by external variables. By using mixed effects models I found that most of the variables tested were not significant in explaining the variation in the song repertoire or the song versatility. The population sizet-1 with the added effect of arrival date was, however, significant in explaining the variation in the song repertoire, and was with the added effect of NDVI data significant in explaining the variation in the song versatility. If the population size was big the previous year the males tended to have larger song repertoires and higher song versatility. Although not significant, some of the variables showed the same trends as have been found previously. The interaction between age and arrival date was also found to be significant in explaining the song repertoire, but this was, however, most likely caused by two individuals who had plastic song as juveniles, and the significance disappeared when these two individuals were removed. The wing length and plumage colour were shown to have delayed maturation, but the song repertoire did not.