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City dwellers compete with the din of traffic to be heard. And it’s not just urban humans. Sparrows living in San Francisco's Presidio district actually tweet their tunes in a higher register than they did in the past, to be heard over the rumble of cars on the nearby Golden Gate Bridge. So says a study in the journal Animal Behavior.
城市居民往往受困于喧囂的交通噪音。其實不堪其擾的不只是城市居民。舊金山要塞區麻雀的鳴叫聲實際上比它們以往任何時候的叫聲都要更高——這樣人們才能在駛過附近金門大橋的汽車隆隆聲中聽到它們的鳴叫。這項研究刊登在《動物行為》雜志上。
Researchers compared white-crowned sparrow songs recorded in 1969 and 2005. Over that time span, ambient noise levels went up. And the bird calls were essentially the same—but the more recent one was higher inpitch. The change presumably allows the song to better penetrate the traffic noise.
研究人員比較了白冠麻雀1969年至2005年的叫聲記錄。在這段時間內，環境噪聲分貝直線上升。它們的叫聲基本上還是相同的，但最近音高明顯上升了。據推測，只有這樣它們的叫聲才能穿透交通噪音。
The modern calls carry more weight with the birds too. Because when male sparrows heard the 2005 recordings played back in their territory, they responded more aggressively—swooping in on the speaker with a “get outta here" chirp and flapping their wings at the suspected intruder.
現代鳥類的叫聲顯示它們承載著更多的壓力。因為當雄性麻雀聽到2005年它們的叫聲錄音時，它們的反應更具有侵略性——它們沖著揚聲器俯沖并發出“離開這里”的警告，而且還用翅膀撲打疑似入侵者。
The researchers say most species simply can't handle the noise and cramped habitats of the city, and head to the country. The adaptable sparrow, however, simply changed its tune.
研究人員說，大多數物種完全無法應對噪音對它們的影響，也無法適應擁擠的城市棲息地，最終只能逃到鄉下去。然而，適應了這種城市噪音的麻雀則完全改變了它們鳴叫聲。
