研究：疫情封城期间鸟类叫声更低、沟通更顺畅

一项研究显示，在美国加利福尼亚州的旧金山湾，封城期间交通噪音的下降致使该地区的白冠麻雀改变了其叫声的音量和质量。它们用更轻柔的声音“歌唱”，歌声变得更美，而且传得更远。

San Francisco birds started singing differently in the quiet of the coronavirus lockdown, says a study in Science.

《科学》杂志的一项研究称，旧金山的鸟儿在安静的疫情封锁期间叫声发生了改变。

Before, urban white-crowned sparrow's breeding territories were almost three times as loud as rural territories, the study found.

研究发现，之前白冠麻雀在城内繁殖地区的噪音是乡下的三倍。

But during the pandemic, researchers noted that noise levels in urban areas were drastically lower. In fact, they were consistent with traffic flow in the mid-1950s.

但是在疫情期间，研究人员注意到，城区的噪音大大降低。事实上，这一噪音水平和上世纪50年代中期的交通噪音水平持平。

"In other words, the Covid-19 shutdown created a silent spring across the SF Bay Area," researchers noted.

研究人员指出：“换言之，疫情封锁给旧金山湾带来了一个安静的春天。”

By analyzing traffic flow data from the Golden Gate Bridge, researchers found that vehicle crossings from April to May 2020 returned to levels not seen since 1954. While noise recordings are not available from the 1950s, researchers said this indicates that a brief but dramatic change in human behavior effectively erased more than a half-century of urban noise pollution.

通过分析金门大桥的车流量数据，研究人员发现，2020年四月至五月的车流量回落到了1954年以来的最低水平。尽管无法获得20世纪50年代的噪音资料，但研究人员表示，这表明人类行为的短时间剧变有效消除了持续半个多世纪的都市噪音污染。

Birds responded by producing higher performance songs at lower amplitudes, maximizing communication distance and salience.

鸟类对此的反应是用更低的振幅（音量）唱出更优美的歌声，更好地进行沟通，让叫声传到更远的距离。

"We found that birds sang more softly when noise levels were lower," researchers said in the study.

研究人员在报告中写道：“我们发现，当噪音水平降低时，鸟儿叫声更轻柔。”

Even though the birds were singing more softly, the study found that communication distance nearly doubled, elevating species fitness and increasing mating potential.

虽然鸟儿用更轻柔的声音唱歌，但研究发现它们的沟通距离几乎翻倍，增强了物种的体力，提高了交配的可能性。

"In addition, the signal-to-noise ratio doubled, which helps explain media reports suggesting that bird songs sounded louder during the shutdown," the researchers said.

研究人员称：“此外，信号噪声比的加倍有助于解释媒体关于鸟叫声在封锁期间听起来更嘹亮的报道。”