Sometimes very swiftly. 有时极为迅速

296. After a thousand years of living in this city,
     在城市居住了上千年之后
297. pigeons are now having to learn to avoid a fish
     鸽子现在却要学会避开水里的鱼
298. Our cities are always changing.
     我们的城市在不断变化
299. Sometimes very swiftly.
     有时极为迅速
300. And animals must cope with the changes,
     动物们必须应对这些改变
301. or disappear.
     否则就会消失
302. One of the greatest changes in recent times
     近年来 最大的变化之一

来自《行星地球 第二季 第六集 Planet Earth S02E06 城市》第 299 行