[Objectives] Bird songs serve the functions of territory defense and mate attraction. Many bird species exhibit high singing activity both in the early morning and at dusk. However, most studies on bird songs typically focus on morning vocalizations rather than those at dusk. Since bird song characteristics are typically influenced by a range of internal and external factors, the different environmental conditions between morning and dusk may lead to variations in songs within the same species, such as differences in acoustic parameters or qualitative characteristics. However, such differences have only been verified in a limited number of species, and whether this phenomenon exists in most bird species with bimodal singing patterns remains unclear. In this study, we investigated the songs of Light-vented Bulbuls (Pycnonotus sinensis), a common small urban songbird with prominent singing behaviors during both morning and dusk, aiming to compare the song differences between these two periods and analyze the potential underlying causes. [Methods] Recordings of Light-vented Bulbul songs were collected between mid-April and mid-May 2019. Sampling was conducted on clear days during two specific time periods:morning (6:00 ~ 9:00) and dusk (16:00 ~ 19:00). The study was carried out in Hongshan District, Wuhan, where songs were recorded from 15 different territories, each separated by at least 1 km (Fig. 1). A total of 302 songs were recorded during the morning, while 268 were recorded at dusk. For each male’s song, the following parameters were measured and calculated:1) frequency parameters:maximum frequency, minimum frequency, frequency range, and peak frequency; 2) temporal parameters:song duration and between-song interval; 3) energy parameters:aggregate entropy and average entropy; 4) qualitative characteristics:number of syllables per song and number of syllable types per song. Additionally, we examined syllable type occurrence rate, song type occurrence rate, song type variants occurrence rate, and song type variability. Spectrograms for a song type example and its song type variants are shown in Fig. 2. To examine whether there were differences in the song characteristics of Light-vented Bulbuls between morning and dusk, we calculated the mean values and coefficients of variation (CVs) for each acoustic parameter of each individual. A repeated measures multivariate analysis of variance (repeated measures MANOVA) was conducted to compare the overall song parameters of Light-vented Bulbuls between morning and dusk. The syllable type occurrence rate, song type occurrence rate, song type variants occurrence rate, and song type variability were compared between morning and dusk by the Wilcoxon signed-rank test. All statistical analyses were performed in IBM SPSS Statistics for Windows, version 22.0 (IBM Corp., Armonk, N.Y., USA). [Results] There were no significant overall differences in song characteristics between the two periods (repeated measures MANOVA, Pillai’s Trace, F_9,6 = 1.931, P >0.05). Similarly, no significant overall differences were found in the CVs of these parameters between morning and dusk (Pillai’s Trace, F_10,5 = 1.610, P >0.05). Song parameters and their CVs between morning and dusk are presented in Tables 1 and 2. Each Light-vented Bulbul produced an average of 5.0 ± 1.4 syllable types, 1.3 ± 0.5 song types, and 3.2 ± 1.4 variants per song type during morning singing. During dusk, the averages were 5.1 ± 1.1 syllable types, 1.1 ± 0.4 song types, and 3.2 ± 2.1 variants per song type. At the same recording sites, individuals used the same song types in both morning and dusk periods (Fig. 3). There were no significant differences between morning and dusk in syllable type occurrence rate (Wilcoxon signed rank test, Z₁₄ = -0.738, P = 0.480), song type occurrence rate (Z_{14 = -0.057, P = 0.978), song type variants occurrence rate (Z14 = -0.966, P = 0.359), or song type variability (Z14 = -0.255, P = 0.832). [Conclusion] There are no significant differences in the aforementioned acoustic parameters of Light-vented Bulbul’s songs in the study area, suggesting that the characteristics, stability, and overall qualitative characteristics of the birds’ songs remain consistent between the morning and dusk periods. It is hypothesized that the diurnal variations in environmental factors within the same habitat is insufficient to cause significant changes in the song characteristics of Light-vented Bulbuls, and social factors may potentially mask the effects of these environmental changes. Therefore, it can be concluded that there are no significant difference between the morning and dusk songs of Light-vented Bulbuls in the study region. This study contributes to filling the gap in the research on the vocal behavior of Light-vented Bulbuls and provides new insights into the dynamic patterns of bird vocalizations.}