1. When the lemmings' food supply becomes too low to support the population, a singular migration commences. 当旅鼠的食物供应不足以维持种群时,一次特别的迁徙就开始了。
2. However, when the lemmings' food supply becomes too low to support the population, a singular migration commences. 然而,当旅鼠的食物供应变得太少而无法维持种群时,一次特别的迁徙就开始了。
3. During the Maastrichtian, a regression commences. 在马斯特里赫特时期,回归开始了。