| Birdsong is essential for the life span of birds, and it is especially important classification feature and biological characteristic. Avian song learning has become a major model system to understand language development in nature. Birdsong and human language have something in common. Both songbirds and humans learn their vocalizations in a period of their early life termed the sensitive period. They must go through a sensitive period of language learning, which begins some time after fledging in birds, at post hatching day(PHD) 10+, and strengthen the practices by day after tomorrow, then they may have common with that of a birdsong characteristic. Moreover, previous studies suggest that sleep can affect vocal learning and development in humans and zebra finches(Poephila guttata). However, these basic aspects of song learning have been rarely documented in wild birds. In this study, we made a preliminary study for the song learning behavior and its mechanism of the young varied tits(Parus varius).To explore the song development process of young varied tits, songs of ten pairs of adult individuals and their chicks were recorded between May and June 2013 in Xianrendong National Nature Reserve(XNNR), Liaoning province. The acoustic characteristics of songs were measured and analyzed by professional software Avisoft SAS Lab Pro software, and compared with the male adult song. The young birds began to produce faint begging call from PHD 1~2 and the frequency ranged for 4000~6000 Hz. The begging call enhanced with the day increasing, and gradually appear double syllable, and multi-syllable verses. Subsong appeared from PHD 15, but it did not like the adult song. Proportion of single syllable verse and double syllables verse decreased as day increase, while the multi-syllable verses gradually increased.To explore the song learning process of young varied tits, 12 varied tits were captured from their nests in Xianrendong National Nature Reserve at PHD 1~2 in May 2013. During the period of 1-90 days three different tutor songs were played to train the nestlings, and recorded the song of all nestlings. Then used the professional software Avisoft SAS Lab Pro software to measure and analyze the acoustic characteristics of songs. Results showed that most individuals began to sing the subsong from PHD 15 and acquired mature song at about PHD 46~60. The sensitive period of song learning in varied tits was from PHD 25~53. There were significant difference of maximum frequency before and after night-sleep, and the maximum frequency of song before night-sleep was significantly higher than that after night-sleep. In this study, all experimental birds learned the exclaiming tutor song, which is the most common song all year around. The other two tutor songs occurred mainly during the breeding season to defend territory and attract mates, and no bird learned these two tutor songs.In order to reveal the molecular mechanisms of birdsong learning, the key gene Fox P2 which is related to birdsong were explored, and the expression of Fox P2 in the brain of varied tit during different learning period were examined. Immunohistochemical results showed that Fox P2 had a high level expression in the time of song learning, especially in the sensitive period. In area X and striatum areas, the Fox P2 genes had the greatest expression. These results suggest that Fox P2 may play a crucial role in fast song learning during sensitive period. The molecular mechanism of birdsong learning can provide information for the study of human developmental language. Overall, our findings describe timings, processes and mechanisms of song development, and demonstrate the importance of the song learning in birdsong development in wild populations. |
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