The implied information is that these types of birds know the right times to migrate, which means to fly from one place to another at different times of the year for feeding or breeding. (See: [[rc://en/ta/man/jit/figs-explicit]])
The abstract noun "migrations" can be translated using the verb "migrate." Alternate translation: "They migrate" or "They fly from one region to another" (See: [[rc://en/ta/man/jit/figs-abstractnouns]])