One example is research in Colorado showing that American robins that migrate to high-altitude summer habitats arrive early and wait longer for the winter snow to melt before mating.

• 最近的一个例子是美国科罗拉多州的旅鸫，研究显示，他们提早迁徙到较高海拔的夏季栖境，然后花了较长的时间等待雪融，才能开始交配。