疫情封城期間鳥類叫聲更低、溝通更順暢

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

《科學》雜誌的一項研究稱，舊金山的鳥兒在安靜的疫情封鎖期間叫聲發生了改變。

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

研究發現，之前白冠麻雀在城內繁殖地區的噪音是鄉下的三倍。

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.

但是在疫情期間，研究人員注意到，城區的噪音大大降低。事實上，這一噪音水平和上世紀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.

研究人員指出：“換言之，疫情封鎖給舊金山灣帶來了一個安靜的春天。”

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.

通過分析金門大橋的車流量數據，研究人員發現，2020年四月至五月的車流量回落到了1954年以來的最低水平。儘管無法獲得20世紀50年代的噪音資料，但研究人員表示，這表明人類行爲的短時間劇變有效消除了持續半個多世紀的都市噪音污染。

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

鳥類對此的反應是用更低的振幅（音量）唱出更優美的歌聲，更好地進行溝通，讓叫聲傳到更遠的距離。

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

研究人員在報告中寫道：“我們發現，當噪音水平降低時，鳥兒叫聲更輕柔。”

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

雖然鳥兒用更輕柔的聲音唱歌，但研究發現它們的溝通距離幾乎翻倍，增強了物種的體力，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.

研究人員稱：“此外，信號噪聲比的加倍有助於解釋媒體關於鳥叫聲在封鎖期間聽起來更嘹亮的報道。”