The song repertoire across avian species varies considerably in size, and reliable measurement is important in defining its significance as a target in sexual selection. In this study, the song structure and song repertoire size of the Daurian Redstart (Phoenicurus auroreus) in South Korea were investigated. The songs had major syllable variation rather than song type variation. The average song repertoire size from 20 males was 39.9 ± 5.8 (range: 28-50), based on a syllable type that was appropriate for this species. The songs were structured with three distinguishable parts, where song syllables varied most in the syllable part, and new syllable additions were relatively limited in the whistle and subsyllable parts. Furthermore, new syllables were gradually reduced with an increasing number of males, potentially due to the existence of core syllables in the songs. Our results suggest an individual identity cue may exist in the syllable part of the song and that the less variable whistles within and between individuals may play a role in forming a local dialect. Thus, further research on syllable similarity is needed to find song variations among individuals over greater geographic distances.

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The threat of predation is the main cause of bird nest abandonment, with such behaviour imposing considerable energetic costs on breeding birds. However, for several species, nest abandonment can be a less costly alternative to complete brood failure. In this study, we examined nest abandonment among Eurasian Tree Sparrows (Passer montanus) by surveying 71 Tree Sparrow nests with various types of entry holes and conducted artificially manipulating some of the entrance shapes. We found that nest abandonment was caused by changes to the nest entry shape in seven cases and by human interference in two cases. Nest abandonments occurred throughout the breeding season, and breeding pairs attempted to breed again immediately after nest abandonment. The results of the artificial nest entry shape manipulation experiment showed that nine of twelve nests (75.0%) were abandoned where the nest entrance holes were widened, and six of eleven nests (54.5%) were abandoned where the nest entrance holes were narrowed. However, none of the nests were abandoned where the entry shape was unchanged. Thus, nest abandonment by Tree Sparrows is correlated with nest entry shape manipulation and is more likely to occur when the energy cost of breeding again is less than that of abandoning the nest.

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Bird call, which is widely used in all species of birds, is short, simple, and functionally diverse in comparison to song. Here, we have recorded call types of Eurasian tree sparrows ( Passer montanus) at multiple situations and various communal behaviors. The Eurasian tree sparrow belongs to the oscine (song-learning) group of songbirds, but their calls are more developed than their song. The calls are used to communicate a variety of behaviors in their social flock. In this study, we categorized call types and usages in relation to the situation on the basis of visual categorization of spectrograms and descriptive measurements. Adult Eurasian tree sparrows have 9 call types (including 9 sub-types at A1 family) and chicks have one (including 2 sub-types). Each call type could be classified as A1 contact call, A2 Fight-intention call, A3 Aerial call, A4 Alarm/Anxiety call, A5 Emergency call, A6 Warning/Threat call, A7 Stimulate call, A8 Screaming call, A9 Social calling, and C1 Begging call. Our results suggest that the diversity of Eurasian tree sparrow’s call types is related to the complex social structure of the species, and might be associated to evolution of sociality. Further research on correlation between various call types and social behavior is needed to find social communication characteristics of Eurasian tree sparrows and other social weaver species with similar ecology may reveal whether evolutionary pressures of sociality lead to increased call complexity.