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.文化进化不仅会导致鸟类种群内不同习得鸣唱类型的流行度发生变化，还会改变鸣唱内部的不同组成部分。1980年至2011年间，我们对某岛屿种群的雄性沙鹀（Savannah sparrow, Passerculus sandwichiensis）单支鸣唱的不同组成部分的变化进行了观测。起始音段未发生变化。嗡鸣音段也表现出相似的稳定性：尽管曾出现过一种罕见的低频变体并随后消失，但1980年与2011年的嗡鸣音段基本一致。由组装为多种类型的离散音素组成的中间音段则具有变异性，不过，中间音段的形态并不会影响适合度（fitness），其功能可能是标识个体身份。终端颤音段在三十年间的出现频率与时长均持续下降。时长更长的颤音与更低的繁殖成功率（reproductive success）相关，这表明颤音时长处于性选择（sexual selection）的选择压力之下。穿插于起始音段之间的鸣唱音素也与繁殖成功率相关。1980年至1982年间出现的高频音簇（high cluster）到2011年已完全消失，并逐渐被咔嗒音序列（click trains）取代，而后者与更高的繁殖成功率相关。在研究的最后十年中，咔嗒音序列中加入了更多咔嗒音。时长更长的咔嗒音序列可能需要更高超的鸣唱技艺（vocal virtuosity），因此能够体现雄性个体的质量（male quality），同样与更高的繁殖成功率相关。在本研究的三十年跨度内，颤音时长与咔嗒音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）的标志性特征。在沙鹀相对简短且简单的习得鸣唱中，文化进化似乎由针对不同鸣唱段的不同机制所介导，这或许是因为各鸣唱段传递的信息各不相同。