Data from: Three decades of cultural evolution in Savannah sparrow songs

Cultural evolution can result in changes in the prevalence not only of different learned song types within bird populations but also of different segments within the song. Between 1980 and 2011, we examined changes within different segments of the single songs of male Savannah sparrows, Passerculus sandwichiensis, in an island population. Introductory notes did not change. The buzz segment showed similar stability; although a rare low-frequency variant appeared and then disappeared, the buzz segments from 1980 and 2011 were essentially identical. The middle segment, made up of discrete notes assembled into several types, was variable. However, the form of the middle segment did not affect fitness and may serve to denote individual identity. The terminal trill decreased steadily in frequency and duration over three decades. Longer trills were associated with lower reproductive success, suggesting that trill duration was under sexual selection. The notes sung between introductory notes were also associated with reproductive success. A high cluster sung in 1980–1982 disappeared altogether by 2011, and was gradually replaced by click trains, which were associated with greater reproductive success. During the final decade of the study, more clicks were added to click trains. Longer click trains, which may require vocal virtuosity and so indicate male quality, were also associated with greater reproductive success. Both trill duration and the number of clicks increased in variance during the three-decade span of the study. We suggest that such increases in variance might be a signature of directional cultural selection. Within the Savannah sparrow’s relatively short and simple learned song, cultural evolution appears to be mediated by different mechanisms for different song segments, perhaps because the segments convey different information.文化演化（cultural evolution）不仅可引发鸟类种群内不同习得鸣唱类型（learned song type）的出现频率变化，还会改变鸣唱内部不同片段的流行情况。1980年至2011年间，我们针对某岛屿种群的雄性萨凡纳带鹀（Savannah sparrow，Passerculus sandwichiensis）的单次鸣唱不同片段的变化展开了研究。鸣唱的起始音节（introductory notes）未发生变化。颤音片段（buzz segment）同样保持稳定：尽管曾有罕见的低频变体出现后又消失，但1980年与2011年的颤音片段基本一致。由离散音节组合为多种类型的中间片段则具有变异性。不过，中间片段的形式并不影响个体适合度（fitness），其功能或为标识个体身份。终末颤音（terminal trill）的出现频率与持续时长在30年间持续下降。颤音越长，个体的繁殖成功率（reproductive success）越低，这表明颤音持续时长受到性选择（sexual selection）的作用。起始音节之间鸣唱的音节同样与繁殖成功率相关。1980年至1982年间鸣唱的高频音簇（high cluster）至2011年完全消失，并逐渐被咔嗒音串（click trains）取代，而咔嗒音串与更高的繁殖成功率相关。在研究的最后10年中，咔嗒音串的咔嗒音节数量有所增加。更长的咔嗒音串可能需要高超的鸣唱技艺，因此可体现雄性个体的质量，其同样与更高的繁殖成功率相关。在本研究的30年周期内，颤音持续时长与咔嗒音节的数量的变异程度均有所提升。我们认为，这种变异程度的提升可能是定向文化选择（directional cultural selection）的特征标志。在萨凡纳带鹀相对简短且简单的习得鸣唱中，文化演化似乎由针对不同鸣唱片段的不同机制所介导，这或许是因为不同鸣唱片段传递的信息各不相同。