Eventually they begin following a microlight , and after several weeks are ready for their major trip south .

终于有一天，它们开始学会追随滑翔机了，几周之后，南飞的准备工作就绪。

Dr robertson is working on a twin-engined electric microlight with a wingspan of 10 metres ( 33 feet ) and a lift-to-drag ratio of 18:1 .

robertson博士正在致力于制造一架双发电动飞机，它有着10米（33英尺）的翼展，升阻比为18:1。