Abstract:[Objectives] There are significant seasonal variations in the acoustic communication of many animals, as does the bird song. Bird song that functions in mate attraction and territory defense should differ somewhat between the breeding and non-breeding seasons, but how? And in what specific ways? This is not yet known in many bird species. In this study, Light-vented Bulbuls Pycnonotus sinensis, a common urban songbird species, which also have significant singing behavior in autumn (non-breeding season), were focused on to examine the seasonal variations in their songs. [Methods] Song characteristics of Light-vented Bulbuls in spring (breeding season) and those in autumn were compared. Song recordings of 27 males in spring and 30 males in autumn were collected respectively from 2020 to 2021 in Wuhan, China (Fig. 1). 372 songs in spring and 435 songs in autumn were measured and analyzed. The following song parameters were measured and calculated for songs of each male (Fig. 2): 1) song parameters on frequency: maximum frequency, minimum frequency, frequency range, peak frequency; 2) song parameters on timing: song duration, between-song interval, song rate, peak time relative; 3) song parameters on energy distribution: aggregate entropy, average entropy; 4) song parameters on quality traits: number of syllables per song, number of syllable types per song and song type occurrence rate (number of song types / number of songs recorded per individual, equivalent to song repertoire). Multivariate analysis of variance (MANOVA) is used to compare the overall difference of all song parameters between season groups. If there is a significant difference, each song parameter is then compared separately between seasons (independent sample t-test). The song types shared by Light-vented Bulbuls in spring and in autumn were analyzed from spectrogram inspection. [Results] Results suggested that there were significant differences between breeding and non-breeding seasons in the following two song parameters of Light-vented Bulbuls: song duration and number of song syllables per song (both P < 0.01) (Table 1). Song durations of Light-vented Bulbuls in spring are significantly longer, and the numbers of syllables per song in spring are also significantly more than those in autumn, while song parameters on frequency, energy distribution and song type occurrence rate did not show significant differences between seasons (all P > 0.05) (Table 1). Light-vented Bulbuls in the same recording site were found to share song types across seasons (Fig. 3). [Conclusion] In summary, this study suggested that only the song timing characteristics (song duration) and syllable numbers per song of Light-vented Bulbuls show significant seasonal plasticity. Light-vented Bulbuls’ longer songs in spring with more syllables indicated their song output in spring is more than that in autumn, reflecting the song behavior in spring is more active, which is consistent with the fact that birds invest more energy for breeding success during breeding season than in non-breeding season. It is speculated that Light-vented Bulbuls still need to defend territories and food resources through singing in autumn and their autumn songs are believed to mainly function in intraspecific competition. This study provides further evidence for understanding the seasonal variations and the function of bird song.