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 sparrows breeding territories were almost three times as loud as rural territories, the study found.But during the pandemic, researchers noted1 that noise levels in urban areas were drastically lower. In fact, they were consistent with traffic flow in the mid-1950s.In other words, the Covid-19 shutdown created a silent spring across the SF Bay Area, researchers noted.By analyzing2 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 recordings3 are not available from the 1950s, researchers said this indicates that a brief but dramatic change in human behavior effectively erased4 more than a half-century of urban noise pollution.Birds responded by producing higher performance songs at lower amplitudes5, maximizing communication distance and salience.We found that birds sang more softly when noise levels were lower, researchers said in the study.Even though the birds were singing more softly, the study found that communication distance nearly doubled, elevating species fitness and increasing mating potential.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.
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1 noted adj.著名的，知名的 参考例句： The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。 Jim is noted for arriving late for work.吉姆上班迟到出了名。
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