提问句出自一片介绍鸟类迁徙的科普文章，全句是：He then set up experiments with caged starlings and found that their orientation was, in fact, in the proper migratory direction except when the sky was overcast, at which times there was no clear direction to their restless movements.
意思是：随后，他用笼子关着的八哥进行试验，结果发现八哥们（飞）的方向实际上是准确的迁徙方向。除非天空乌云蔽日，这时，它们的躁动不...
